Omental torsion is a rare cause of acute abdomen resulting from the twisting of the greater omentum or omental appendages around their vascular pedicle. It occurs in two forms: primary (idiopathic) and secondary (related to adhesions, hernias, cysts, or tumors). The primary form is associated with obesity and male sex; bipedicular fixation of an omental segment and pendulous fat tissue create susceptibility to rotation. Clinically, it mimics right lower quadrant pain and is frequently confused with acute appendicitis — the vast majority of patients undergo surgery with a presumptive diagnosis of appendicitis, and the diagnosis is made intraoperatively. On CT, pathognomonic findings include the 'whirl sign' (swirling omental vascular pedicle), a fat-density mass, and surrounding fat stranding/haziness (misty mesentery). It shares a spectrum with omental infarction, but the whirl sign in torsion is the distinguishing feature. Inflammation and edema increase fat tissue density and produce reactive thickening of the adjacent peritoneum. Treatment is generally conservative (pain management, anti-inflammatory) but complicated cases (necrosis, abscess) may require surgical resection.
Age Range
25-60
Peak Age
40
Gender
Male predominant
Prevalence
Rare
Omental torsion begins when the free distal segment of the greater omentum undergoes axial rotation around its proximal fixation point. Rotation initially obstructs venous drainage → venous congestion and edema develop → interstitial edema fluid accumulates in omental fat tissue → on CT, fat density increases (normally -100 to -80 HU → in torsion -40 to -20 HU) and a hazy fat appearance (misty omentum) develops. Continued rotation also compromises arterial supply → hemorrhagic infarction ensues → necrotic fat tissue further densifies and acquires heterogeneous density. The twisting vascular pedicle creates concentric layers on CT forming the 'whirl sign' — this finding results from spiraling mesenchymal tissue and vascular structures appearing as a vortex pattern on axial images. The inflammatory process spreads to surrounding peritoneal surfaces → reactive peritoneal thickening and free fluid (usually small amounts) accumulate. Necrotic omental tissue shows hyperintensity on T1 due to paramagnetic methemoglobin and heterogeneous signal on T2 due to edema. On ultrasound, the torsed omentum appears as a hyperechoic mass — edema and hemorrhage within fat tissue create acoustic impedance differences.
Visualization on contrast-enhanced CT of the omental vascular pedicle twisting in concentric rings/spirals on axial section — direct evidence of torsion and the pathognomonic finding distinguishing omental torsion from simple omental infarction.
On non-contrast CT, a fat-density (-40 to +20 HU) oval or wedge-shaped mass is seen in the anterior peritoneal space (usually right-sided). It is denser than normal omental fat (due to edema and hemorrhage). Prominent fat stranding and haziness surround the mass. The mass is independent of the bowel wall — bowel wall thickening as seen in appendicitis or diverticulitis is absent. This feature is critical in distinguishing the diagnosis from epiploic appendagitis and omental infarction.
Report Sentence
A __ mm fat-density oval mass is seen in the anterior peritoneal space with prominent surrounding fat stranding; consistent with omental torsion/infarction.
On portal venous phase contrast-enhanced CT, the swirling of the omental vascular pedicle in axial section (whirl sign) is seen. This finding results from the torsed omental vessels and mesenchymal tissue appearing as spiraling concentric layers. The whirl sign is usually located cranial to or at the center of the mass lesion and indicates the torsion axis. Because vessels are opacified in the contrast phase, the whirl sign is more conspicuous than on non-contrast CT. This finding is the most important criterion distinguishing omental torsion from simple omental infarction.
Report Sentence
A whirl sign is identified in the omental vascular pedicle, supporting the diagnosis of omental torsion.
In the arterial phase, dilated, engorged omental vessels are seen in the torsed omental segment. While normal omental vessels are thin and barely visible, in torsion, venous drainage obstruction causes the vessels to dilate and become conspicuous. As arterial supply continues while venous return is obstructed, contrast enters the torsed segment in the arterial phase but return is delayed → focal hyperemic enhancement may be seen in the omental mass. In advanced stages where arterial occlusion also occurs, loss of enhancement (avascular area) develops — this indicates necrosis.
Report Sentence
Dilated omental vessels and focal hyperemic enhancement are seen in the torsed omental segment; consistent with venous congestion.
In the portal venous phase, reactive thickening and enhancement of peritoneal surfaces adjacent to the torsed omental mass are seen. The parietal peritoneum appears as a smooth, thin enhancing line. Accompanying small amounts of free peritoneal fluid (reactive ascites) are frequently present — typically collecting in the pelvis or Morrison's pouch. Peritoneal thickening indicates spread of the inflammatory process to peritoneal surfaces and should not be confused with peritoneal carcinomatosis — in torsion, thickening is focal and smooth, while in carcinomatosis it is diffuse and nodular.
Report Sentence
Reactive peritoneal thickening and a small amount of free fluid are seen adjacent to the torsed omental mass.
On B-mode ultrasound, the torsed omentum appears as a non-compressible hyperechoic oval mass in the anterior peritoneal space. The mass is usually located between the abdominal wall and ascending colon. Its internal structure may be homogeneous or mildly heterogeneous — hemorrhage and necrosis areas can create hypoechoic foci. Tenderness with probe compression (sonographic Murphy-like sign) is positive. Small amounts of free fluid are often accompanying. Ultrasound is usually the first-line imaging modality but has lower diagnostic accuracy than CT — rather than making a specific diagnosis, it is reported as 'inflammatory pathology other than acute appendicitis' and CT is recommended.
Report Sentence
A __ mm non-compressible hyperechoic oval mass is seen between the abdominal wall and colon in the right lower quadrant; consistent with omental pathology (torsion/infarction).
On color Doppler ultrasound, the torsed omental mass shows reduced or completely absent vascularity. In the early stage (partial torsion), peripheral vascularity may be preserved but central flow loss is notable. In the advanced stage (complete torsion), no Doppler signal is seen throughout the mass — this finding suggests necrosis development. Increased vascularity from reactive hyperemia in surrounding tissue may be seen — this halo-like peripheral flow increase represents the inflammatory response. Power Doppler is more sensitive to low flow velocities than color Doppler and is more useful in demonstrating residual flow in partial torsion.
Report Sentence
No vascularity is demonstrated within the omental mass on Doppler examination, consistent with torsion/necrosis; reactive hyperemia is present in surrounding tissue.
On T2-weighted MR images, the torsed omentum appears as a mass with heterogeneous signal. While fat tissue basally shows intermediate-hyperintense signal on T2, edema areas add marked hyperintensity and hemorrhage areas add variable signal depending on stage. Early subacute hemorrhage (methemoglobin) may be hypointense on T2, while late subacute hemorrhage appears hyperintense. On STIR sequences, fat is suppressed and edema becomes more conspicuous — the torsed omental mass stands out from surrounding suppressed fat. The whirl sign can be identified on axial T2 MR images as well, but is not as easily recognized as on CT.
Report Sentence
A __ mm mass showing hyperintense signal on STIR in the anterior peritoneal space is seen, consistent with edema and inflammation; suggesting omental torsion/infarction.
Criteria
Spontaneous torsion of the omentum without underlying predisposing factors. Associated with obesity, male sex, and omental anatomical variations (accessory omentum, bifid omentum). Accounts for 60-70% of cases.
Distinct Features
Usually occurs on the right side (right omental segment is longer and more mobile). Whirl sign may be more prominent because the fixation point is singular. No adjacent organ pathology is seen on CT.
Criteria
Torsion of the omentum around a fixation point of adhesion, hernia, cyst, tumor, or post-surgical fixation. The underlying pathology determines the torsion axis. Accounts for 30-40% of cases.
Distinct Features
Predisposing lesion (hernia defect, cystic lesion, adhesion band) can be identified at the torsion axis on CT. Location may differ from primary form (left side, epigastric region). Treatment must also address the underlying cause.
Criteria
Complete arterial occlusion, extensive necrosis, and potentially secondary infection/abscess formation from prolonged torsion. Clinical presentation shows fever, leukocytosis, and peritoneal irritation signs prominently.
Distinct Features
Gas bubbles within the mass on CT (necrosis/abscess), rim enhancement (abscess wall), more pronounced peritoneal fluid and thickening. Avascular area is larger — loss of enhancement throughout the mass. Indication for surgical resection. Risk of peritonitis in delayed diagnosis.
Distinguishing Feature
Omental infarction does NOT have the whirl sign — this is the most important distinguishing finding. Infarction shows a more homogeneous fat-density mass, while torsion is more heterogeneous with a positive whirl sign. Infarction is usually segmental without vascular pedicle rotation.
Distinguishing Feature
Epiploic appendagitis is much smaller (1-4 cm), showing an oval fat-density nodule with a hyperdense ring (with central dot sign). Omental torsion creates a much larger mass (>5 cm) with positive whirl sign. Epiploic appendagitis is close to/adherent to the bowel wall, while omental torsion is independent of the bowel wall.
Distinguishing Feature
Mesenteric panniculitis is located at the mesenteric root (omental torsion is anterior), showing 'fat ring sign' (preserved perinodal fat ring) and 'tumoral pseudocapsule'. No whirl sign. Panniculitis is chronic, torsion has acute onset.
Distinguishing Feature
Peritoneal carcinomatosis shows diffuse nodular omental thickening (omental cake) — torsion is a focal mass. Ascites is prominent in carcinomatosis with a known primary malignancy history. Torsion presents with acute pain, carcinomatosis has an insidious course.
Urgency
urgentManagement
conservativeBiopsy
Not NeededFollow-up
specialist-referralOmental torsion is generally managed with conservative treatment — pain control (NSAIDs) and clinical follow-up. Most cases show spontaneous resolution within 1-2 weeks. Complicated cases (necrosis, abscess, peritonitis findings) require surgical resection (omentectomy) — laparoscopic approach is preferred. CT is sufficient for diagnosis; no biopsy needed. Since it clinically mimics acute appendicitis, preoperative CT can prevent unnecessary surgery. For conservatively treated patients, 1-2 weeks clinical follow-up and control CT if symptoms do not improve are recommended.
Omental torsion is generally self-limiting. Diagnosis prevents unnecessary surgery. Conservative management (NSAIDs) sufficient in most cases. Surgery may be needed if necrosis develops.