Body Radiology

Trauma · GI · GU · OB/GYN · Hepatobiliary

Anatomy

Anatomy References

CT abdomen/pelvis labelling

Additional Resources

Small Bowel Obstruction

RadioGraphics

Liver Segments (Couinaud)

Segments I–VIII based on hepatic veins (divide segments) and portal veins (divide right vs left). Functional right lobe: V–VIII. Functional left lobe: I–IV. Right hepatic vein: divides VI/VII from V/VIII. Middle hepatic vein: true lobar fissure (with gallbladder fossa).

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Interactive Liver Atlas

liveratlas.org

Fluid Hounsfield Units

Fluid	HU Range
Simple fluid / transudate	0–10
Bile	−80 to 20
Urine	0–20
Contrasted urine	80–200
Serum	0–20
Unenhanced clotted blood	30–45
Clotted blood	60–90
Contrast-enhanced blood	120+

Trauma

Trauma — Resources

AAST Injury Scoring (all organs)

AAST.org

Liver Injury Grading — AAST

Advance one grade for multiple injuries up to grade III.

Grade	Type	Description
I	Hematoma	Subcapsular, <10% surface area
I	Laceration	Capsular tear <1 cm parenchymal depth
II	Hematoma	Subcapsular, 10–50% surface area; intraparenchymal <10 cm diameter
II	Laceration	Capsular tear 1–3 cm parenchymal depth, <10 cm length
III	Hematoma	Subcapsular >50% surface area or expanding; ruptured subcapsular or intraparenchymal hematoma; intraparenchymal >10 cm or expanding
III	Laceration	>3 cm parenchymal depth
IV	Laceration	Parenchymal disruption 25–75% of hepatic lobe or 1–3 Couinaud segments within a single lobe
V	Laceration	Parenchymal disruption >75% of hepatic lobe or >3 Couinaud segments within single lobe
V	Vascular	Juxtahepatic venous injuries (retrohepatic vena cava/central major hepatic veins)
VI	Vascular	Hepatic avulsion

📋 Reporting Checklist — Liver Injury

Lobe(s) involved; laceration depth; subcapsular / intraparenchymal hematoma size
Active hemorrhage (arterial blush): present / absent
Hemoperitoneum: absent / small / moderate / large
Vascular injury: juxtahepatic IVC, central hepatic veins (Grade V); hepatic avulsion (Grade VI)
Biloma / bile leak: suspected perihepatic collection
AAST grade

Renal Injury Grading — AAST

Advance one grade for bilateral injuries up to grade III.

Grade	Type	Description
I	Contusion	Microscopic or gross hematuria; urologic studies normal
I	Hematoma	Subcapsular, nonexpanding; no parenchymal laceration
II	Hematoma	Nonexpanding perirenal hematoma confined to renal retroperitoneum
II	Laceration	<1.0 cm parenchymal depth of renal cortex; no collecting system rupture or urinary extravasation
III	Laceration	>1.0 cm parenchymal depth of renal cortex; no collecting system rupture or urinary extravasation
IV	Laceration	Parenchymal laceration extending through renal cortex, medulla, and collecting system
IV	Vascular	Main renal artery or vein injury with contained hemorrhage
V	Laceration	Completely shattered kidney
V	Vascular	Avulsion of renal hilum which devascularizes kidney

📋 Reporting Checklist — Renal Injury

Side(s); laceration depth; perirenal hematoma
Collecting system: intact vs. urinary extravasation
Active hemorrhage: present / absent
Renal vasculature: intact / hilar injury / devascularization
AAST grade

Splenic Injury Grading — AAST

Advance one grade for multiple injuries up to grade III.

Grade	Type	Description
I	Hematoma	Subcapsular, <10% surface area
I	Laceration	Capsular tear <1 cm parenchymal depth
II	Hematoma	Subcapsular, 10–50% surface area; intraparenchymal <5 cm diameter
II	Laceration	Capsular tear 1–3 cm parenchymal depth; does not involve trabecular vessels
III	Hematoma	Subcapsular >50% surface area or expanding; ruptured subcapsular or intraparenchymal; intraparenchymal hematoma ≥5 cm or expanding
III	Laceration	>3 cm parenchymal depth or involving trabecular vessels
IV	Laceration	Involving segmental or hilar vessels producing major devascularization (>25% of spleen)
V	Laceration	Completely shattered spleen
V	Vascular	Hilar vascular injury which devascularizes spleen

📋 Reporting Checklist — Splenic Injury

Laceration depth; subcapsular / intraparenchymal hematoma size
Splenic vascular injury: pseudoaneurysm / active extravasation
Perisplenic hematoma; hemoperitoneum volume
AAST grade

Bladder Rupture

Type	Location	Key Feature
Intraperitoneal	Dome (weakest point)	Contrast tracks along bowel loops, paracolic gutters — surgical repair
Extraperitoneal	Anterolateral wall	Contrast in perivesical space (flame-shaped); usually assoc. with pelvic fracture — catheter drainage often sufficient
Combined	Both	Surgical repair

Extraperitoneal bladder rupture: non operative management.

Intraperitoneal bladder rupture - extending around loops of bowel; operative management

📋 Reporting Checklist — Bladder Rupture

Type: extraperitoneal (EPR) / intraperitoneal (IPR) / combined — per CT cystography
Defect location: anterior wall / posterior wall / dome / bladder neck
Extent of extravasation: EPR (flame-shaped perivesical) / IPR (contrast outlining bowel loops)
Pelvic hematoma: size and location (perivesical / pre-sacral)
Associated pelvic ring fracture: present / absent
Urethral injury signs: urethral disruption / Foley catheter malposition
Foley catheter position: within bladder / malpositioned / not present

Urethral Injuries

Type I — Stretch/elongation, no extravasation · Type II — Partial disruption above UGD · Type III — Complete disruption above UGD (most common posterior injury) · Type IV — Bladder neck injury · Type V — Partial/complete anterior urethral injury

Retrograde urethrogram required to evaluate for urethral injury before catheter placement in pelvic fracture with blood at urethral meatus, perineal bruising, or inability to void.

Pancreatic Injury Grading — AAST

Advance one grade for multiple injuries up to grade III. Proximal pancreas = to the patient's right of the superior mesenteric vein.

Grade	Type	Description
I	Hematoma	Minor contusion without duct injury
I	Laceration	Superficial laceration without duct injury
II	Hematoma	Major contusion without duct injury or tissue loss
II	Laceration	Major laceration without duct injury or tissue loss
III	Laceration	Distal transection or parenchymal injury with duct injury
IV	Laceration	Proximal transection or parenchymal injury involving ampulla
V	Laceration	Massive disruption of pancreatic head

Key CT signs: Peripancreatic fluid/stranding · Parenchymal laceration (low-attenuation line) · Ductal injury suggested by complete transection or peripancreatic fluid tracking along duct · MRCP or ERCP for definitive duct assessment. Grade III–V injuries typically require surgery or endoscopic intervention.

📋 Reporting Checklist — Pancreatic Injury

Location: head / neck / body / tail
Main pancreatic duct: intact / probable disruption / transection
Peripancreatic fluid / stranding: absent / present
Active hemorrhage: present / absent
AAST grade; recommend MRCP or ERCP if Grade III+ suspected

📄Radiopaedia — Pancreatic trauma

Bowel & Hollow Viscus Injury — CT Imaging

Key principle: Any free intraperitoneal air in a trauma patient without prior laparotomy = bowel perforation until proven otherwise. Bowel injury is frequently missed on initial CT — mesenteric findings often precede definitive bowel wall signs. Free fluid without solid organ injury is an important indirect sign warranting careful bowel evaluation or repeat imaging.

Finding	Significance	Notes
Pneumoperitoneum	Direct sign — perforation	Check anterior subdiaphragmatic space and perihepatic region on CT; even a tiny extraluminal bubble is significant; pneumoretroperitoneum suggests duodenal or colonic injury
Bowel wall discontinuity	Direct sign — laceration/perforation	May be subtle; inspect all bowel loops on coronal/sagittal reformats; full-thickness defect confirms perforation
Extraluminal oral contrast	Direct sign — perforation	Only if oral contrast given; highly specific; oral contrast now rarely used in trauma — absence does not exclude perforation
Mesenteric hematoma	Direct/indirect — mesenteric or bowel injury	Hyperdense blood within mesentery; may indicate vascular pedicle injury or bowel wall laceration; associated with increased risk of delayed perforation
Mesenteric stranding / fat infiltration	Indirect — mesenteric contusion or injury	Haziness and streaking in mesenteric fat; may represent contusion without perforation; serial clinical exam warranted
Bowel wall thickening	Indirect — contusion, hematoma, or ischemia	Circumferential thickening >3–5 mm; hematoma produces symmetric homogeneous thickening; ischemia produces stratified (target) pattern or loss of enhancement
Free fluid without solid organ injury	Indirect — high suspicion for bowel/mesenteric injury	Sensitivity for bowel injury ~70%; must correlate with clinical exam and mechanism; isolated free fluid in blunt trauma = diagnostic laparoscopy consideration
Bowel wall hyperenhancement or non-enhancement	Direct — active hemorrhage or devascularization	Focally absent enhancement = ischemia/infarction; active extravasation = arterial blush within bowel wall

Segment-specific pearls: Duodenum — retroperitoneal position; look for pneumoretroperitoneum, peripancreatic hematoma, duodenal wall thickening; seat-belt mechanism; associated pancreatic injury common. Small bowel — most commonly injured hollow viscus in blunt trauma; lap belt injury pattern (Chance fracture + bowel injury). Colon — less commonly injured bluntly; consider penetrating mechanism; ascending and sigmoid most vulnerable.

📄Radiopaedia — Small bowel trauma

Trauma in Pregnancy

Key principle: Do not withhold indicated imaging — maternal health is critical to fetal health. Typical trauma CT (abdomen/pelvis) delivers ~25 mGy to the fetus, well below the 50 mGy safety threshold. Prompt diagnosis of maternal injury protects both mother and fetus. IV iodinated contrast is safe in pregnancy (FDA Category B). Gadolinium: avoid unless benefits clearly outweigh fetal risk (FDA Category C).

CT Fetal Radiation Doses

CT Examination	Fetal Dose Estimate (mGy)	Notes
Head CT	~0	Safety threshold: 50 mGy. Doses <50 mGy: no proven fetal harm. Doses 200–250 mGy: potential neural tube defects. Intellectual disability risk highest at 8–15 weeks gestation.
Chest CT / CTPA	0.2
Abdominal CT	4
Low-dose stone protocol	10
Abdomen & pelvis CT	25
Abdomen & pelvis CT angiography	34

Clinical algorithm: Hemodynamically unstable + FAST positive → laparotomy without further imaging delay. Hemodynamically stable: FAST first → if positive for free fluid or signs of peritonitis → CECT abdomen/pelvis. If FAST negative but clinical concern remains → CECT if indicated. US useful for targeted fetal assessment and gestational age confirmation at any stage. Laparotomy vs. observation in stable patients may be guided by CT findings and gestational age (>24 weeks → fetal monitoring).

Obstetric Injuries — Placental Abruption

Most important obstetric injury: Occurs in 20–50% of pregnant patients experiencing major trauma. Second most common cause of fetal death after maternal shock. US sensitivity is low — 50–80% of traumatic abruptions are missed prospectively at initial US. External fetal monitoring is more sensitive than US for abruption detection and should always be performed for at least several hours after trauma (even seemingly minor trauma, as 1–5% of "minor" cases result in abruption).

Feature	CT Findings	US Findings
Acute hematoma / abruption	Heterogeneous placenta; area(s) of hypoattenuation or nonenhancement; retroplacental hyperattenuating blood; large retroplacental hematomas undermine placental tissue	Retroplacental collection (hyperechoic acutely, becomes hypoechoic / isoechoic as hemorrhage evolves — improving conspicuity on follow-up US)
Normal variants (false positives) — review	Cotyledons, venous lakes, chorionic plate indentations, age-related infarcts — may mimic hypoattenuation. Geographic hypoattenuation is NOT specific for abruption.	Prominent venous lakes may mimic retroplacental hematoma — correlate with CT
Complete abruption	Total absence of placental perfusion/enhancement; associated hemoperitoneum	Avascular placenta on Doppler; absent or abnormal fetal cardiac activity
Rupture of membranes	Large volume of fluid in vagina with low volume of residual amniotic fluid; heterogeneous placenta	Oligohydramnios / anhydramnios; fluid in vagina

📄Radiopaedia — Traumatic placental abruption (case example)

Traumatic Abruptio Placenta Scale (TAPS) — CT Grading

Grades based on degree of placental enhancement on CECT. Intended for 2nd and 3rd trimester. Clinical diagnosis of abruption must be present for grading to apply.

Grade	Placental Enhancement	Clinical Management
0	100% — homogeneous normal enhancement	Normal; expectant management; good clinical outcomes expected
1	>50% — small geographic hypoattenuation (likely normal variants: cotyledons, venous lakes, age-related infarcts)	Normal; expectant management; good clinical outcomes expected
2a	>50% — nongeographic hypoattenuation, full thickness, acute angles with myometrium	Increased probability of abruption; extended clinical monitoring recommended
2b	25–50% — larger area of decreased enhancement	Increased probability of abruption; extended clinical monitoring recommended
3	<25% — near-complete devascularization	Fetal death occurs frequently; consider immediate cesarean delivery if abruption confirmed

Uterine Rupture

Feature	Details
Incidence & significance	~0.6% of trauma in pregnancy; fetal mortality approaches 100%; maternal mortality ~10% (not typically the primary injury causing maternal death)
CT findings	Myometrial wall defect (most commonly fundus or anterior uterine wall); fetal parts external to uterine contour; hemoperitoneum; complex fluid adjacent to perforation site; diffusely heterogeneous uterus
US findings	Uterine contour defect; fetal parts outside uterus; intraperitoneal fluid; may be used intraoperatively
Risk factors	Prior cesarean delivery; prior uterine surgery; congenital anomalies; scarring. Blunt and penetrating mechanisms both implicated.

Fetal Injuries

Injury	Details
Direct fetal injury	Rare (<1% of trauma cases). Fetus relatively protected in 1st trimester by pelvic bones. Risk increases with gestational age as fetus grows and head may engage the pelvis.
Fetal skull fractures	CT more sensitive than US for bone detail. Fetal death in up to 35% when pelvic fracture present. Linear nondisplaced — monitoring without surgical intervention. Depressed fractures — percutaneous or surgical elevation. Fetal ICH may be associated.
Fetal intracranial hemorrhage	Identifiable on CT; associated with skull fractures; deceleration mechanism. Intrauterine fetal death may result.
Rib / long bone fractures	May be seen on CT with severe pelvic trauma or direct compression. Multiple fetal fractures raise concern for severity of impact.
Penetrating trauma	Gravid uterus provides protection by displacing abdominal organs; uterine musculature slows projectiles. Severe fetal injury in 60–70% of penetrating trauma; fetal mortality 71–73% with gunshot wounds to the gravid uterus.

Nonobstetric Maternal Injuries — Pregnancy-Specific Considerations

Structure	Pregnancy-Specific Risk
Spleen	Displaced superiorly by gravid uterus; splenomegaly from increased blood volume → increased susceptibility to rupture from blunt or penetrating trauma
Liver	Displaced superiorly and compressed against rib cage; higher risk of laceration
Bowel	Displaced peripherally by uterus; increased risk of injury with penetrating trauma (less protection by uterus laterally)
Bladder	Elevated out of pelvis by gravid uterus; extraperitoneal rupture common (peritoneal reflection is below the displaced bladder). CT cystography or delayed CT imaging recommended if pelvic fracture + hematuria or clinical suspicion.
Pelvic fractures	Maternal mortality up to 9%. Pelvic fracture is not an absolute contraindication to vaginal delivery but increases risk of fetal skull fracture if head is engaged. Fetal death in up to 35% when pelvic fracture present.
Vascular	Increased pelvic blood flow → higher risk of severe hemorrhage after blunt or penetrating pelvic trauma

📋 Reporting Checklist — Trauma in Pregnancy

Placenta: estimate percentage of normal enhancement (TAPS grade if 2nd/3rd trimester); retroplacental or marginal hematoma; size of hypoattenuating area
Myometrium: wall contour intact or defect present; fetal parts within or outside uterine contour
Amniotic fluid: volume (oligohydramnios / anhydramnios); fluid in vagina (premature rupture of membranes)
Fetal: position (cephalic / breech / transverse); estimated gestational age; skull fractures; intracranial hemorrhage; long bone or rib fractures
Free fluid: intraperitoneal location and density (HU consistent with blood); hemoperitoneum volume estimate
Solid organs: liver, spleen, kidneys — AAST injury grade; active hemorrhage (contrast blush)
Pelvic ring: fracture type; acetabular involvement; proximity to fetal head
Bladder: wall integrity; extravasation on delayed images; cystography findings if performed

📄Langdon JH, Chai N, Patel A, et al. Imaging of Trauma in Pregnant Patients. RadioGraphics. 2025;45(10):e240043. https://doi.org/10.1148/rg.240043

Gunshot Injuries

Ballistic fundamentals:
Low-velocity (<2,000 fps) — handguns and most civilian firearms. Injury from permanent cavitation (tissue crushed directly by projectile) only. Tissue destruction limited to projectile diameter + fragmentation.
High-velocity (>2,000 fps) — rifles and military weapons. Add temporary cavitation: pressure wave expands a transient cavity far larger than the bullet diameter, causing indirect injury to structures not directly contacted. Organs tolerating stretch (lung, muscle) handle this better than those that do not (brain, liver, spleen, kidney, bowel).
Shotgun — range-dependent: close range (<3 m) delivers high-energy injury comparable to rifle; intermediate range produces spreading pellet pattern; distant range (>7 m) deposits pellets in subcutaneous tissue only.

Secondary projectiles: Bullet fragments and bone chips driven off by impact become high-velocity secondary missiles, extending the zone of injury well beyond the primary bullet path. When a bullet strikes cortical bone, resulting bone fragments can lacerate adjacent neurovascular structures, even if the primary projectile did not directly contact them. Always evaluate structures adjacent to any bone impact site.

CT Trajectory Assessment — Structures to Evaluate by Zone

Zone	Critical Structures Along Path	Key CT Findings
Neck (Zones I–III)	Carotid arteries, vertebral arteries, jugular veins, trachea, esophagus, spinal cord, brachial plexus	Expanding hematoma; pseudoaneurysm; occlusion/dissection on CTA; tracheal air leak; esophageal perforation (periesophageal gas, fluid); epidural hematoma; cord signal change on MRI
Chest	Aorta/great vessels, heart/pericardium, trachea/bronchi, esophagus, lung parenchyma, diaphragm	Hemothorax; pneumothorax; pulmonary laceration; pericardial effusion/hemopericardium; mediastinal hematoma; diaphragmatic defect (herniated bowel/omentum); esophageal gas; aortic pseudoaneurysm on CTA
Abdomen / Pelvis	Liver, spleen, kidneys, bowel (small + large), mesenteric vessels, bladder, urethra, iliac vessels, lumbosacral plexus	Solid organ lacerations (AAST grade); free fluid (blood vs bowel contents); pneumoperitoneum; mesenteric fat stranding/hematoma; active extravasation on CTA; pelvic fracture with vascular injury; perineal gas (rectal injury); extraperitoneal bladder rupture
Spine	Vertebral bodies, spinal cord/cauda equina, epidural space, paraspinal muscles	Vertebral body fracture/comminution; intracanalicular bullet or bone fragment; epidural hematoma; bullet trajectory crossing midline predicts cord injury; paraspinal hematoma
Extremities (MSK)	Long bones, major arteries/veins, peripheral nerves, joints, compartments	Comminuted fracture with bone fragment dispersal; periosteal stripping; intraarticular fragments; expanding soft tissue hematoma; absent distal flow on CTA; compartment syndrome (muscle edema, obliteration of fat planes)

Intraarticular Bullet / Fragment

Report explicitly — clinical consequences are high:
Lead toxicity: Synovial fluid is mildly acidic and dissolves lead → systemic absorption → plumbism (anemia, encephalopathy, neuropathy). Risk is highest when the bullet is within a synovial joint or bursa; fragments in soft tissue or bone carry lower but real risk if near vascular structures.
Joint sepsis: Bullet carries skin flora along the tract; intraarticular entry creates a direct pathway for infection.
Articular cartilage injury: Metallic debris and bone chips cause mechanical damage and degenerative change.
Surgical extraction is generally indicated for intraarticular projectiles.

Retained Projectile — MRI Considerations

Most civilian lead bullets and copper-jacketed rounds are non-ferromagnetic and are generally considered MRI-conditional or safe. Steel-jacketed military rounds (full metal jacket with steel core) may be ferromagnetic — obtain prior radiographs to assess composition before MRI.
Metallic fragments in or near the orbit, spinal canal, or major vessels are high-risk regardless of composition. MRI artifact (susceptibility) can limit evaluation of adjacent structures — CT may be preferred for trajectory assessment near retained fragments.

📋 Reporting Checklist — Gunshot Injuries

Projectile accounting: number visible on scout/XR; correlate with entry/exit wounds to determine retained vs. passed through
Trajectory: describe projected path (entry zone → exit zone or retained location); note crossing midline, traversing body cavities, proximity to named structures
Bone injury: fracture pattern, degree of comminution; bone fragment dispersal (secondary missiles); periosteal stripping
Intraarticular involvement: bullet or fragment within joint space — specify joint; note articular surface injury
Vascular: expanding hematoma, pseudoaneurysm, occlusion, active extravasation (CTA if trajectory near major vessels)
Hollow viscus: free air, mesenteric stranding/hematoma, bowel wall discontinuity (GI perforation → high infection risk from bacterial seeding along tract)
Solid organ: laceration grade (AAST), subcapsular hematoma, devascularized segment, active extravasation
Spine: vertebral fracture, intracanalicular fragment, epidural hematoma; trajectory crossing spinal canal
Compartment syndrome: muscle edema, loss of fat plane definition, fascial integrity; flag if trajectory through a tight compartment (leg, forearm, thigh)
Retained foreign material: location (intraarticular / soft tissue / bone / vascular / spinal canal); MRI safety note if relevant
Recommended additional imaging: CTA for vascular injury, CT cystogram for pelvic trajectory near bladder, MRI spine for cord compression

📄Sodagari F et al. Gunshot Wounds: Mechanisms, Radiologic Manifestations, and Complications. RadioGraphics. 2020;40(6):1756–1788.

Other

Acute Appendicitis

CT criteria: Appendix diameter >6mm (outer wall to outer wall) + wall thickening + periappendiceal fat stranding. Appendicolith present in ~30% (increases perforation risk). MRI preferred in pregnancy and pediatrics. CT sensitivity ~94%, specificity ~95%.

Finding	CT	US	Notes
Appendix diameter >6mm	Outer wall–outer wall; distended with fluid	Non-compressible tubular structure >6mm	Primary criterion; measure at widest point
Periappendiceal fat stranding	Haziness/streaking in periappendiceal fat	Echogenic surrounding fat	Increases specificity when combined with dilation
Appendicolith	Calcified focus within appendiceal lumen; extraluminal if perforated	Shadowing echogenic intraluminal focus	~30% of cases; associated with perforation/gangrene
Wall enhancement/thickening	Stratified wall enhancement; wall >2mm	Hyperechoic mucosa with thickened layers	Loss of enhancement = gangrenous/necrotic wall
Perforation signs	Free air (RLQ), periappendiceal abscess (rim-enhancing collection), phlegmon	Free fluid RLQ; disrupted wall layers	Perforation rate ~20–30%; IR drainage for abscess >3cm
Non-visualization	May be normal (retrocecal, pelvic) or suggest alternative diagnosis	Non-visualization common (~20–30%); proceed to CT in adults	Always report explicitly — do not call normal

Perforated appendicitis: Localized free extraluminal air in RLQ · Periappendiceal abscess · Phlegmon (ill-defined mass without discrete rim) · Free fluid in RLQ/pelvis. Gangrenous appendicitis: Absent mural enhancement · Intraluminal gas · Focal wall defect. Both require urgent surgical or IR consultation.

Pearls: State diameter + fat stranding + appendicolith separately in report. Retrocecal appendix (~26%): may present with flank pain — ensure full coronal/sagittal review. Tip appendicitis: isolated inflammation of the tip, may be subtle.

📄Radiopaedia — Acute appendicitis

📋 Reporting Checklist — Appendicitis

Appendix diameter: measure outer wall to outer wall (mm; >6mm abnormal)
Periappendiceal fat stranding: present / absent
Appendicolith: present / absent; location (tip / body / base)
Wall enhancement: normal stratified / loss of mural enhancement (gangrenous)
Perforation signs: localized free air / phlegmon / abscess (size if present)
Appendix position: retrocecal / pelvic / pre-ileal / other
Free fluid: present / absent; location
Alternative diagnosis if appendix not visualized

Adrenal Washout Calculator

APW = absolute percentage washout; RPW = relative percentage washout
Lesion Type	HU Criteria
Adrenal adenoma (lipid-rich)	Unenhanced HU ≤10
Adrenal adenoma (washout)	APW ≥60% OR RPW ≥40%
APW formula	(Enhanced − Delayed) / (Enhanced − Unenhanced) × 100
RPW formula	(Enhanced − Delayed) / Enhanced × 100
Pheochromocytoma	Often >10 HU unenhanced; avoid washout protocol if suspected
Myelolipoma	Macroscopic fat (very low HU, <-30)

🔗

Adrenal Washout Calculator

pcheng.org

Bowel Ischemia

Critical finding: Pneumatosis intestinalis (intramural gas) + portal venous gas = grave prognosis — indicates advanced bowel necrosis with transmural infarction. Report immediately and obtain urgent surgical consultation. Distinguish pneumatosis from intraluminal gas: pneumatosis follows bowel wall contour, seen on multiple planes, often linear or bubbly in pattern.

SMA embolus vs thrombosis: SMA embolus: filling defect typically 3–10 cm from SMA origin (beyond origin at middle colic artery), often cardiac source (Afib, endocarditis); spares proximal jejunum. SMA thrombosis: occlusion at or near SMA origin, atherosclerotic disease, ischemia of entire SMA territory including proximal jejunum; longer segment ischemia; prior intestinal angina history.

Etiology	CT Findings	Territory
SMA occlusion — embolus	Filling defect in SMA 3–10 cm from origin; bowel wall thickening → thinning (necrosis); pneumatosis; portal venous gas; lack of bowel wall enhancement; mesenteric stranding	Mid-jejunum to transverse colon; spares proximal jejunum and duodenum (SMA branches beyond origin occluded)
SMA occlusion — thrombosis	Atherosclerotic calcification/plaque at SMA origin; near-complete or complete occlusion at origin; extensive small bowel and right colon ischemia; collateral vessels may be visible	Entire SMA territory including proximal jejunum; duodenum may be involved; longer ischemic segment than embolus
SMV thrombosis	Hyperdense SMV (acute thrombus); filling defect in SMV ± portal vein; mesenteric edema and ascites (venous congestion); bowel wall thickening (target sign/halo); hemorrhagic infarction more common than arterial; pneumatosis less common early	Variable; often patchy; mesenteric venous distribution; may spare arterially supplied areas; hypercoagulable states, portal hypertension, pancreatitis
Non-occlusive mesenteric ischemia (NOMI)	Patent mesenteric vessels; diffuse bowel wall thickening; poor bowel wall enhancement; mesenteric edema; no filling defect; SMA vasospasm may be visible on angiography	Watershed areas most vulnerable: splenic flexure, sigmoid; diffuse distribution possible; ICU/low-flow states, dialysis, vasopressors
Colonic ischemia (watershed)	Bowel wall thickening ± thumbprinting (submucosal edema); pericolonic stranding; watershed zones; typically no occlusion on CT; pneumatosis in severe cases	Splenic flexure (Griffiths point) and rectosigmoid junction (Sudeck point) — watershed zones between SMA/IMA and IMA/internal iliac territories
Strangulation / closed-loop	Closed loop morphology + wall thickening + loss of enhancement + mesenteric engorgement + ascites + pneumatosis; combination of arterial and venous compromise due to twisting	Isolated closed loop; variable size; sigmoid or internal hernia most common; rapidly progressive to full-thickness necrosis

📄Menke J. Diagnostic accuracy of MDCT for acute mesenteric ischemia: A systematic review. Eur Radiol. 2010;20(12):2805-14.

📄Radiopaedia — Bowel ischaemia

Bowel Obstruction

Closed loop obstruction — surgical emergency: Two adjacent transition points creating an isolated loop with no decompression. Signs: C- or U-shaped dilated loop, mesenteric swirl (twisted mesentery), beak sign (tapered ends at transition), whirl sign (twisting of mesenteric vessels/fat), dilated loop with wall thickening or pneumatosis. Requires urgent surgical consultation regardless of other findings.

Caliber thresholds: SBO: dilated loops >2.5 cm proximal to transition point with decompressed loops distally. LBO: colon >6 cm (cecum >9 cm = impending perforation / Ogilvie risk). Water-soluble contrast enema or CT colonography can characterize LBO level and etiology. Pneumoperitoneum = perforation.

Feature	SBO (Small Bowel)	LBO (Large Bowel)
Location	Central abdomen; jejunum (left upper) vs ileum (right lower)	Peripheral/frame-like distribution of dilated colon
Caliber threshold	>2.5 cm (small bowel); >3 cm (duodenum)	>6 cm colon; >9 cm cecum = imminent perforation risk
Transition point	Dilated proximal loops → decompressed distal loops; identify cause (adhesion, hernia, mass)	Transition at obstructing lesion (carcinoma, diverticular stricture, volvulus); may have competent ileocecal valve → closed loop cecal distension
Closed loop	C/U-shaped dilated loop; two transition points; mesenteric swirl; beak sign; high risk of strangulation	Volvulus creates closed loop (sigmoid or cecal); competent ileocecal valve in LBO creates cecal closed loop
Common causes	Adhesions (most common post-surgical), incarcerated hernia (internal or external), Crohn's stricture, malignancy, intussusception, gallstone ileus	Colorectal carcinoma (most common), diverticular stricture, volvulus (sigmoid > cecal), extrinsic compression, Ogilvie syndrome (pseudo-obstruction)

📄Paulson EK et al. Acute small bowel obstruction: CT evaluation. Radiology. 2011;261(3):686-98.

📄Radiopaedia — Small bowel obstruction

📋 Reporting Checklist — Bowel Obstruction

Level: gastric outlet / proximal SBO / distal SBO / LBO
Transition point: location (describe relative to bowel anatomy / quadrant / adjacent structure)
Proximal bowel caliber at transition (mm); degree of dilation
Etiology if identifiable: hernia (type/location) / adhesion band / mass / volvulus / intussusception
Closed loop: present / absent (C/U-shaped loop, mesenteric swirl, beak sign)
Ischemia signs: wall thickening / pneumatosis / portal venous gas / mesenteric haziness / free fluid
Free air: present / absent (perforation)
Decompressed rectum: confirms complete obstruction

Gallbladder & Biliary Emergencies

Emphysematous cholecystitis: Gas in the gallbladder wall (intramural) or lumen on CT = gas-forming organisms (Clostridium, E. coli). Seen in diabetics, elderly, vascular disease. High mortality (15–25%) — emergent cholecystectomy (percutaneous cholecystostomy if too ill). Do not confuse with intraluminal gas (normal post-procedure) — intramural gas follows wall contour, non-dependent, linear/bubbly.

Gangrenous cholecystitis CT findings: Intraluminal membranes (desquamated mucosa — pathognomonic), irregular/asymmetric wall thickening, absent or asymmetric wall enhancement, pericholecystic fluid/stranding, discontinuous mucosal line. Perforation: pericholecystic abscess, free fluid, defect in wall. Higher surgical morbidity than uncomplicated cholecystitis.

Diagnosis	US Findings	CT Findings	Urgency
Acute cholecystitis	Gallstones + sonographic Murphy sign (tenderness with probe over GB); GB wall thickening >3 mm; pericholecystic fluid; GB distension (>5 cm transverse)	GB wall thickening; pericholecystic fat stranding; GB distension; impacted stone in neck/cystic duct; periportal edema	Urgent cholecystectomy within 72h or percutaneous cholecystostomy in poor surgical candidates
Gangrenous cholecystitis	Intraluminal membranes (echogenic strands); absent Murphy sign (denervation); irregular wall; no wall vascularity on Doppler	Intraluminal membranes; wall irregularity/asymmetry; absent wall enhancement; pericholecystic abscess; pneumobilia	Emergent — higher complication rate; perforation risk; urgent surgical consultation
Emphysematous cholecystitis	Echogenic foci in wall with "dirty shadowing" or ring-down artifact (gas); may obscure GB anatomy	Gas in GB wall (intramural, non-dependent) and/or lumen; pericholecystic gas; may have associated liver abscess	Emergent cholecystectomy; gas-forming organisms; diabetic emergency; high mortality
Choledocholithiasis	Hyperechoic foci in CBD with posterior acoustic shadowing; CBD dilatation >6 mm (>8 mm post-cholecystectomy); visualized in ~50% by US	Hyperdense foci in CBD on non-contrast; MRCP superior for stones <3 mm; impacted ampullary stone at distal CBD; biliary dilatation	Urgent ERCP if cholangitis or obstructive jaundice; elective if asymptomatic
Cholangitis (Charcot's / Reynolds pentad)	Biliary dilatation; CBD stones; GB stones; may show periportal edema; abscess formation in severe cases	Biliary dilatation; obstructing stone or stricture; periportal edema; hepatic abscesses (pyogenic); pneumobilia (post-sphincterotomy or emphysematous); portal vein thrombosis	Emergent — Charcot's triad (RUQ pain, fever, jaundice) ± Reynolds pentad (+ shock + AMS). IV antibiotics + urgent biliary decompression (ERCP preferred); ICU level care
Gallstone ileus	Distended bowel loops; large ectopic gallstone; biliary-enteric fistula (pneumobilia); may show cholecystoduodenal fistula	Rigler's triad: SBO + ectopic gallstone + pneumobilia; stone typically at terminal ileum (narrowest point); Bouveret syndrome = gastric outlet obstruction (duodenal impaction)	Urgent surgical enterolithotomy; fistula repair at same or staged procedure depending on patient stability
Mirizzi syndrome	Impacted stone in GB neck/cystic duct causing extrinsic compression of CHD; proximal biliary dilatation with normal distal CBD; gallbladder contracted	Stone impacted at GB neck; fusiform narrowing of CHD/CBD at cystic duct level; biliary dilatation above; choledochal fistula in advanced cases (type II–IV)	Urgent — high surgical complexity; ERCP pre-op for biliary drainage; cholecystectomy ± biliary reconstruction; distinguish from malignancy (Klatskin tumor)

📄Shakespear JS et al. CT findings of acute cholecystitis and its complications. AJR. 2010;194(6):1523-9.

📄Radiopaedia — Acute cholecystitis

📋 Reporting Checklist — Cholecystitis

Gallbladder wall thickness (mm; >3mm abnormal if fasting)
Sonographic Murphy sign: positive / negative / not assessed
Gallstones: present / absent; location (neck / body / fundus impaction)
Pericholecystic fluid / fat stranding: present / absent
GB distension: transverse diameter (>5cm abnormal)
Intraluminal membranes or sloughed mucosa (gangrenous features): present / absent
Wall enhancement on CT: hyperenhancing / heterogeneous / absent
Gas in GB wall or lumen (emphysematous): present / absent — surgical emergency
Biliary dilation: CBD diameter; choledocholithiasis present / absent

Diverticulitis

CT findings: Colonic diverticula + pericolonic fat stranding + colonic wall thickening at site of inflammation. Sigmoid colon >90%. CT sensitivity ~97%, specificity ~100%. Hinchey classification guides management of complicated disease.

Stage	Description	Management
Hinchey Ia	Pericolic/mesenteric phlegmon or confined pericolic abscess (<4 cm)	IV antibiotics; most resolve conservatively
Hinchey Ib	Pericolic abscess >4 cm	IV antibiotics ± percutaneous drainage if accessible
Hinchey II	Pelvic, retroperitoneal, or distant abscess	Percutaneous drainage; elective surgery after resolution
Hinchey III	Purulent peritonitis (ruptured pericolonic abscess)	Surgical emergency
Hinchey IV	Feculent peritonitis (free colonic perforation)	Surgical emergency; highest mortality

Complicated Feature	CT Findings	Management Implication
Contained perforation / phlegmon	Pericolonic gas bubbles + inflammatory mass; no free pneumoperitoneum	IV antibiotics; admission; most resolve without intervention
Free perforation	Pneumoperitoneum; diffuse peritoneal enhancement; ascites	Surgical emergency (Hinchey III/IV)
Abscess	Rim-enhancing fluid collection adjacent to or distant from colon; may contain gas	>3–4 cm = IR percutaneous drainage; elective sigmoid resection 6–8 weeks later
Fistula	Colovesical: air/fecal matter in bladder · Colovaginal: air in vagina	Surgical repair after bowel prep; colovesical most common
Obstruction	LBO/SBO from extrinsic compression by phlegmon or fibrosis	NG decompression; surgical consult if complete

Surgical emergency: Free air + diffuse peritoneal enhancement = Hinchey IV. Always report free intraperitoneal air with diverticulitis — even small amounts change management.

📄Radiopaedia — Hinchey classification

Ectopic Pregnancy

Ruptured ectopic — hemorrhagic emergency: Free pelvic/abdominal fluid + positive β-hCG = ruptured ectopic until proven otherwise. Do NOT delay for MRI. Hemodynamically unstable patient goes directly to OR. Hemodynamically stable: US to confirm. Hemoperitoneum extending to Morrison's pouch or paracolic gutters = large hemorrhage.

Heterotopic pregnancy: Simultaneous intrauterine and ectopic pregnancy. Rare in general population (~1:30,000) but significantly increased with ART (~1:100–500). Presence of an intrauterine pregnancy does NOT exclude a co-existing ectopic. Always evaluate adnexa even when IUP is confirmed in ART patients.

Finding	Description
Empty uterus with β-hCG >1500–2000 mIU/mL	Discriminatory zone: β-hCG above which IUP should be visible on TVUS (1500–2000 mIU/mL for TVUS; 6500 mIU/mL for transabdominal). Empty uterus above discriminatory zone = ectopic or failed IUP. Note: heterotopic can have IUP + ectopic simultaneously.
Ring of fire sign	Trophoblastic "ring of fire" Doppler signal around ectopic sac; echogenic ring on B-mode ("bagel sign"); distinct from the ovary (surrounded by ovarian parenchyma = corpus luteum cyst); TVUS most sensitive
Tubal ring sign / extrauterine gestational sac	Round or oval adnexal structure separate from ovary; may contain yolk sac or embryo (definitive diagnosis); Doppler: "ring of fire" around ectopic sac (trophoblastic flow)
Free pelvic fluid (hemorrhage)	Non-dependent echogenic free fluid in cul-de-sac, Morrison's pouch, paracolic gutters; complex/echogenic = hemoperitoneum; simple free fluid less specific; volume correlates with degree of hemorrhage
Interstitial ectopic	Gestational sac within myometrium at cornual region; interstitial line sign (echogenic line connecting ectopic sac to endometrium); thin myometrial rim <5 mm; presents later (8–12 weeks) with greater hemorrhage risk than tubal ectopic; 2–4% of ectopics; high mortality

📄Barnhart KT. Ectopic pregnancy. N Engl J Med. 2009;361(4):379-87.

📄Radiopaedia — Ectopic pregnancy

📋 Reporting Checklist — Ectopic Pregnancy

β-hCG level vs discriminatory zone (>1500–2000 mIU/mL should demonstrate IUP)
Uterine findings: IUP present / empty uterus / pseudogestational sac
Adnexal ring sign: location (tubal / interstitial / ovarian / cervical)
Gestational sac contents: yolk sac / embryo (CRL in mm if visible)
Cardiac activity: present / absent
Free pelvic fluid: location / amount / echogenicity (hemorrhagic = ruptured)
Myometrial rim thickness if interstitial (<5mm = high rupture risk)
Heterotopic pregnancy consideration if ART patient

Epiploic Appendagitis & Omental Infarct

Clinical importance: Both are self-limiting conditions treated conservatively (NSAIDs, analgesia). Both clinically mimic appendicitis or diverticulitis. CT is diagnostic and avoids unnecessary surgery and antibiotics. Report confidently when findings are characteristic to prevent unnecessary admission or intervention.

Feature	Epiploic Appendagitis	Omental Infarct
Location	Immediately adjacent to colon wall (sigmoid most common, then cecum/ascending); antimesenteric border	Larger area of right-sided omentum most common (right lower quadrant > right upper quadrant); not directly attached to colon
Size	Small, ovoid; typically 1.5–3.5 cm; proportional to appendage size	Larger; typically >3–5 cm; cake-like fatty mass; may be very large (>10 cm)
Central hyperdense dot	Central hyperdense focus (thrombosed central vessel) within fatty lesion — characteristic sign (~70%)	Absent (no central vessel); heterogeneous fatty stranding without central dot
Fat stranding pattern	Oval pericolonic fat with thin hyperattenuating rim (inflamed/thrombosed epiploic appendage); surrounding inflammation limited	Diffuse, cake-like omental fat stranding; less well-defined; no discrete rim; larger area of involvement
Self-limiting	Yes — resolves in 2–4 weeks; rarely recurs; conservative management	Yes — resolves in 4–6 weeks; conservative management; rarely requires surgery for refractory cases

📄Singh AK et al. Omental infarct and epiploic appendagitis: imaging characteristics and treatment. Emerg Radiol. 2005;11(2):82-7.

📄Radiopaedia — Epiploic appendagitis

📄Radiopaedia — Omental infarction

Abdominal Wall & Internal Hernias

Type	Location	Contents at Risk	Imaging Clue
Inguinal — indirect	Lateral to inferior epigastric vessels; through deep inguinal ring	Small bowel, omentum, ovary (females)	Contents follow inguinal canal lateral to epigastric vessels
Inguinal — direct	Medial to inferior epigastrics; through Hesselbach's triangle	Small bowel, omentum	Protrudes directly through posterior inguinal canal wall
Femoral	Below inguinal ligament; medial to femoral vein in femoral canal	Small bowel (highest strangulation risk)	Bowel below inguinal ligament medial to femoral vessels; narrow neck
Umbilical	Through umbilical ring defect	Omentum, small bowel	Midline anterior defect at umbilicus; common in obesity, ascites
Incisional	Through prior surgical scar/fascial defect	Small bowel, omentum, colon	Fascial defect at scar; report defect size and contents
Paraduodenal (internal)	Left paraduodenal fossa (Landzert) or right (Waldeyer's); near Treitz	Small bowel	Clustered encapsulated small bowel in LUQ (left) or right of midline; displaced mesenteric vessels
Mesenteric defect (internal)	Through surgically created mesenteric defect; most common post-RYGB	Small bowel, biliopancreatic limb	Swirling mesentery; clustered loops posterior to anastomosis; Petersen's space

Strangulation — report urgently: Bowel wall thickening · Absent bowel wall enhancement · Pneumatosis intestinalis · Mesenteric edema/hemorrhage · Portal venous gas · Free peritoneal fluid. These indicate compromised bowel viability — surgical emergency. Always assess for strangulation when bowel is within any hernia sac.

📄Radiopaedia — Abdominal hernia

Ovarian Torsion

Ultrasound findings: Enlarged ovary (>4 cm, often >5 cm); peripheral follicles displaced to periphery (hallmark — "string of pearls"); ovary displaced from normal position (may be midline or contralateral); absent or decreased Doppler flow; free pelvic fluid; associated adnexal mass (dermoid, cystadenoma) in ~50–60% of cases; thickened edematous stroma.

Critical pitfall: Normal Doppler flow does NOT exclude ovarian torsion. Intermittent torsion or partial torsion can preserve some flow. Clinical presentation + enlarged ovary + peripheral follicles = high suspicion regardless of Doppler. This is a surgical emergency — diagnostic laparoscopy if clinical suspicion is high. Delay causes ovarian infarction and loss.

Pearls: Right > left (sigmoid colon limits left ovarian mobility). Associated ovarian mass in ~50–60% of cases — teratoma, cystadenoma most common. Pediatric patients: torsion can occur with normal ovaries. MRI if equivocal US — T2 hyperintense edematous stroma, absent enhancement in late/infarcted torsion. Doppler twisting of vascular pedicle ("whirlpool sign") is specific but not always present.

📄Shadinger LL et al. Preoperative sonographic and clinical characteristics as predictors of ovarian torsion. J Ultrasound Med. 2008;27(1):7-13.

📄Radiopaedia — Adnexal torsion

📋 Reporting Checklist — Ovarian Torsion

Side: right / left
Ovarian volume: L × W × H × 0.523 (mL); abnormal if >20cc or asymmetrically enlarged
Doppler flow: absent / reduced / asymmetric vs contralateral
Whirlpool sign of vascular pedicle: present / absent
Free pelvic fluid: present / absent; simple / complex / hemorrhagic; amount
Underlying ovarian lesion: size (cm), morphology
Uterine deviation toward affected side: present / absent
Contralateral ovary: normal / abnormal (volume and flow)

Pancreatitis

Revised Atlanta Classification: Interstitial edematous pancreatitis vs. necrotizing pancreatitis (parenchymal and/or peripancreatic necrosis). CT should be performed ≥48-72h after onset for accurate necrosis assessment.

Collection	Timing	Definition
Acute peripancreatic fluid (APFC)	<4 wk	Interstitial pancreatitis; no wall; homogeneous
Pseudocyst	>4 wk	Encapsulated fluid; well-defined wall; from APFC
Acute necrotic collection (ANC)	<4 wk	Necrotizing pancreatitis; contains heterogeneous debris
Walled-off necrosis (WON)	>4 wk	Encapsulated necrosis; endoscopic/surgical drainage

Balthazar Grade & CT Severity Index (CTSI)

Balthazar Grade	CT Finding	Score
A	Normal pancreas	0
B	Focal or diffuse pancreatic enlargement	1
C	Pancreatic inflammation with peripancreatic fat changes	2
D	Single peripancreatic fluid collection	3
E	≥2 peripancreatic fluid collections or gas in/adjacent to pancreas	4

Necrosis	Score	CTSI = Balthazar + Necrosis (max 10)
None	0	0–3: Mild 4–6: Moderate 7–10: Severe	Higher CTSI correlates with increased morbidity and mortality
<30%	2
30–50%	4
>50%	6

📋 Reporting Checklist — Pancreatitis

Necrosis: extent (%) and location — head / body / tail
Peripancreatic fluid collections: number, location, size (cm)
Walled-off necrosis vs pseudocyst: wall thickness, complexity, >4 weeks duration
Pancreatic duct: disruption / dilation (>3mm body, >5mm head) / disconnected duct
Splenic vein thrombosis: present / absent
Pseudoaneurysm: present / absent; vessel involved; size
Biliary: CBD dilation (>8mm) / choledocholithiasis / gallstones

Gastrointestinal Volvulus

Sigmoid volvulus: Massively dilated sigmoid colon >6 cm, apex pointing toward RUQ ("coffee bean" or "bent inner tube" pointing right), loss of haustral markings, convergence of walls at twist site. Cecal volvulus: ileocecal junction identified out of position (cecum absent from RLQ), dilated cecum in left upper abdomen, "coffee bean" opening toward LUQ. Both require urgent decompression or surgery.

Type	Imaging Signs	Notes
Sigmoid volvulus	Massively dilated inverted U-shaped sigmoid loop; apex points to RUQ; "coffee bean" or "bent inner tube" sign on XR; convergence of walls at left pelvis (twist site); loss of haustra; CT: whirl sign at twist, beak sign, dilated sigmoid >6 cm; often massive colonic dilation	Most common volvulus (60–75%); elderly/institutionalized patients; chronic constipation; sigmoid redundancy; endoscopic decompression often successful; high recurrence; sigmoidectomy definitive
Cecal volvulus	Cecum absent from RLQ; dilated ovoid gas-filled cecum in left mid-abdomen or LUQ; "coffee bean" opening toward LUQ; small bowel dilation; CT: whirl sign at ileocecal junction; cecum >10 cm; dilated terminal ileum; appendix may be visible with cecum	Second most common volvulus (25–40%); younger patients; congenital lack of retroperitoneal fixation; right hemicolectomy required; endoscopic decompression generally not definitive; high failure/recurrence rate; cecal bascule variant (folding without twisting)
Gastric volvulus — organoaxial	Stomach rotates around long axis (cardiopyloric axis); greater curvature flips superiorly; two air-fluid levels on upright CXR (double bubble); inversion of stomach; NGT cannot be passed; associated with diaphragmatic defect	More common type; associated with paraesophageal/diaphragmatic hernia; Borchardt triad: severe epigastric pain + retching without vomiting + inability to pass NGT; surgical emergency if strangulation
Gastric volvulus — mesenteroaxial	Rotation around short axis (perpendicular to cardiopyloric axis); antrum rotates anteriorly and superiorly; intermittent symptoms; partial obstruction pattern	Less common; often intermittent and partial; associated with diaphragmatic eventration; may reduce spontaneously; surgical repair of predisposing defect

📄Peterson CM et al. Volvulus of the gastrointestinal tract. AJR. 2009;192(2):W105-15.

📄Radiopaedia — Sigmoid volvulus

📄Radiopaedia — Gastric volvulus (with diagrams)

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Gastric Volvulus Types — Organoaxial & Mesenteroaxial

Radiopaedia

Acute Body MRI

Hepatobiliary Emergencies

Condition	Key MRI Findings	Tips
Choledocholithiasis	T2-hypointense filling defect in bile duct on MRCP. Obstructive: upstream dilatation, abrupt caliber change. Trace entire biliary system on thin MRCP/T2W	GB neck and cystic duct are blind spots. Pneumobilia can mimic calculi (nondependent, blooms on GRE). Crossing vessel on coronal MRCP can mimic filling defect — check axial reformats
Gangrenous cholecystitis	Focal GB wall nonenhancement or discontinuity; intramural abscess (rim-enhancing + diffusion-restricting collection); contained perforation	Abscess: rim enhancement + central DWI restriction. Hematoma: central DWI restriction but no rim enhancement + T1 hyperintensity
Hemorrhagic cholecystitis	Distended GB with T1-hyperintense and T2-hypointense contents; blooming on T2* GRE; active bleed on subtraction images. No enhancement within hematoma itself	Both hemorrhage and inspissated bile are T1-bright — use GRE blooming to distinguish. Check subtraction images for active extravasation
Bile leak / biloma	T2W MRCP: delineate anatomy. Gadoxetate (Eovist) hepatobiliary phase: extravasation of excreted contrast from duct into collection. Add 60–90 min delayed phase if 20–30 min scan is negative	Avoid gadoxetate if bilirubin >3 mg/dL, severe hepatic failure, or competing drugs (methotrexate, tamoxifen, cisplatin)
Hepatic abscess	Rim-enhancing collection + central diffusion restriction; double-target sign; perilesional hyperemia (arterial phase)	Overlaps with cystic metastases — abscess favored by clinical context (fever, leukocytosis, recent biliary intervention). Short-term follow-up if unclear
Hemorrhagic hepatic lesion	Lesion with T1-hyperintense and T2-hypointense blood products; blooming on GRE; nonenhancing hemorrhagic component on subtraction. Look for enhancing viable tumor around hematoma	HCC: check for tumor-in-vein (thrombus enhances like primary tumor). Adenoma: young women, OCP use, peripheral enhancement pattern. Subtraction mandatory when T1 hyperintensity is present

Pancreatic Emergencies

Condition	Key MRI Findings	Tips
Acute interstitial edematous pancreatitis	Pancreatic edema (loss of normal T1 hyperintensity) + peripancreatic fluid on T2W + preserved parenchymal enhancement on post-Gd	Normal pancreas is T1-bright (brighter than liver). Loss of T1 signal = edema/inflammation. DWI restriction is sensitive for early pancreatitis. India ink artifact on out-of-phase shows subtle fat stranding
Acute necrotizing pancreatitis	Lack of parenchymal enhancement on post-Gd = necrosis. Hemorrhage: T1 hyperintensity + GRE blooming. Vascular complications: thrombosis (filling defect on bSSFP/post-Gd), pseudoaneurysm	Pitfall: Diffuse hemorrhagic necrosis can appear T1-bright, mimicking normal pancreas. Always check post-Gd for absent enhancement and T2W for necrosis
Pancreatic trauma	Full-thickness laceration = T2-hyperintense linear signal disrupting parenchyma. Trace pancreatic duct on T2W axial images (MRCP often limited by surrounding fluid)	Ductal injury (AAST Grade III+) = surgical indication. MRI better than CT for delineating duct integrity. Contusions (Grade I/II) without duct injury → conservative

Bowel & Peritoneal

Condition	Key MRI Findings
Appendicitis (pregnancy)	Dilated appendix ≥7 mm, wall thickness >2 mm, periappendiceal fluid/fat stranding on T2W. Appendicolith: T2-hypointense filling defect (confirm on bSSFP). Appendix migrates cranially with gestational age. Sensitivity 94%, specificity 97%
Diverticulitis	Colonic wall thickening >3 mm with diverticula; pericolic fat stranding on T2W FS; abscess: rim-enhancing + DWI-restricting collection. MRI sensitivity 86–94%, specificity 88–92%. Better soft-tissue resolution for fistula, oophoritis
Crohn complications	Stricture: wall thickening >3 mm + luminal narrowing >50% + upstream dilatation. Penetrating: sinus tract, fistula, phlegmon, abscess (rim enhancement + DWI restriction). Active inflammation: wall edema + hyperenhancement on T2W FS and post-Gd
Perianal fistula	Small-FOV T2W FSE along anal canal is key. Report: tract type (Parks classification — intersphincteric / transsphincteric / suprasphincteric / extrasphincteric), internal and external openings, branches, abscess. DWI + post-Gd for abscess vs granulation vs fibrosis
Pneumoperitoneum	Subtle T2-hypointense foci in peritoneal cavity. Air-fluid levels. Susceptibility artifact on bSSFP and T1W GRE sequences. Can be easily missed — look for abnormal extraenteric T2-dark foci

Renal & GU Emergencies

Condition	Key MRI Findings
Pyelonephritis	Wedge-shaped T2 hyperintensity with striated nephogram; wedge-shaped hypoenhancement on post-Gd; wedge-shaped DWI restriction. Abscess: rim-enhancing collection with central DWI restriction
Renal infarct	Wedge-shaped nonenhancement with cortical rim sign (preserved capsular vessel enhancement); cortical DWI restriction
Urolithiasis (pregnancy)	Hypointense filling defect in dilated ureter — better seen on bSSFP than T2W. Distinguish from physiologic hydroureteronephrosis (gradual tapering at pelvic brim, right > left)
Spontaneous renal hemorrhage (Wünderlich syndrome)	Subcapsular/perirenal T1-hyperintense collection with T2 signal heterogeneity. Subtraction images mandatory to exclude underlying enhancing neoplasm (AML, RCC most common causes)

OB/GYN Emergencies

Condition	Key MRI Findings
Placental abruption	Retroplacental or subchorionic hematoma: T1-hyperintense blood products (T1 better than T2 for hemorrhage detection). T2 can underestimate hemorrhage extent. bSSFP may show subchorionic hematoma better than T2
Ectopic pregnancy	Gestational sac outside endometrial cavity on T2W. Locations: tubal (most common), cornual, cervical, cesarean scar. MRI localizes ectopic precisely when US is indeterminate. Cesarean scar ectopic: sac in lower uterine segment scar, residual myometrium <2 mm = rupture risk
Ovarian torsion (pregnancy)	Enlarged ovary with peripheral follicles and stromal edema on T2W. Pelvic ascites. Compare with contralateral ovary. Whirlpool sign of twisted pedicle
Postpartum hemorrhage — RPOC vs UVA	RPOC: enhancing endometrial tissue (≤ myometrium = moderate; > myometrium = hypervascular). Serial β-hCG decreases. UVA/AVF: serpiginous flow voids, early draining vein on time-resolved MRA. Low-flow UVA: myometrial blush without early draining vein

MRI in pregnancy — key principles: Safe at ≤3 T (prefer 1.5 T in 1st trimester). GBCAs are FDA Class C — avoid unless benefit clearly outweighs risk; use lowest dose of macrocyclic Group II GBCA with informed consent. Non-contrast sequences (T2W SSFSE, DWI, bSSFP, T1W) are sufficient for most acute indications. For renal failure (eGFR <15): Group II GBCAs can be used after risk-benefit discussion; space injections ≥7 days apart.

📄Panda A, Aswani Y, Heming CAM, et al. On-Call Body MRI: A Primer. RadioGraphics. 2025;45(1).