Primary Idiopathic Segmental Infarction of the Omentum
Shashank S Prasad*, Paritosh Khanna*, Anagha Joshi**, Anisha A Sawkar***
We report a case of primary idiopathic infarction of the omentum occurring in a 47-year-old female patient diagnosed on Computed Tomography (CT) of the abdomen. These patients generally present with an acute pain usually in the right side of the abdomen. Ultrasonography findings are helpful especially to rule out the other differential diagnostic possibilities but the CT findings are diagnostic of the condition and obviate the need for surgery. The condition is usually self-limiting with the symptoms and findings resolving over time.
Fig. 1 : Plain axial CT scan of the abdomen showing a heterogenous density lesion with intervening areas of fat density and hyper attenuating streaks in the lower right para-umbilical region between the rectus sheath and the ascending colon.
Fig. 2 : Contrast enhanced CT scan of the abdomen at a slightly different level demonstrating no enhancement of the lesion.
A 47-year-old female presented with a history of pain in the right lower quadrant of the abdomen since seven days. On physical examination the patient was afebrile and had tenderness in the right para-umbilical region. The patient’s haemoglobin was 11 gm% and total WBC counts were 13,000 cells/mm3. The renal parameters were normal. Urine pregnancy test was negative. There was no history of any previous surgery.
Ultrasonography of the abdomen revealed a mixed-echogenic, predominantly hyperechoice, ill-defined 6x5x5 cm. sized mass in the lower right para-umbilical region. Further evaluation with CT was advised.
On abdominal Computed Tomography (CT), an approximately 6.2x5x5 cm sized non-enhancing heterogenous density lesion with intervening areas of fat density and hyper attenuating streaks was seen in the lower right para-umbilical region between the rectus sheath and the ascending colon (Figs. 1 and 2). Appendix was normal. A diagnosis of primary segmental omental infarction was made. After seven days, the patient’s symptoms resolved. A follow-up scan demonstrated similar findings with no abscess formation. The patient was discharged after an uneventful hospital course.
Primary idiopathic segmental infarction of the omentum is an uncommon cause of acute abdominal symptoms. Bush first described it in 1869.1 This condition occurs at all ages between 3 and 72 years, with the lowest frequency in the second decade of life. The male to female ratio is 2:1. The most common mode of presentation is pain in the abdomen, with the right lower quadrant being the commonest location.1
The pathophysiology of primary idiopathic segmental omental infarction has been postulated to be secondary to venous idiopathic and thrombosis, either secondary to a heavy meal or a sudden rise in intra-abdominal pressure or due to gravitational pull on the greater omentum in obese individuals.2 The high incidence of right-sided involvement with adherence to the ascending colon, caecum, or anterior peritoneum is best explained by a developmental abnormality. In the embryo, the dorsal mesogastrium develops into the greater omentum and the ventral mesogastrium into the lesser omentum; occasionally an abnormal extension of the ventral mesogastrium develops and later becomes united with the dorsal mesogastrium i.e. the greater omentum. This additional part may become adherent to the ascending colon and even to the caecum and anterior peritoneum (Haller’s ligament). This extension has a precarious blood supply and is liable to infarction.2
The most common mode of presentation is right-sided acute abdominal pain, nausea, vomiting and altered bowel habits.1 At physical examination, the patient has localized tenderness and moderate peritoneal irritation, while laboratory tests show a mild leucocytosis and later an increased erythrocyte sedimentation rate. Body temperature may be normal or slightly elevated. On occasion a lesion can be palpated.3 If the patient undergoes surgery, a firm lesion is found in the right lower portion of the greater omentum, which has an ovoid or cake-like shape. The lesion is located between and attached to the peritoneum and the right hemicolon.3 The pathologic findings are those of a haemorrhagic infarction with fat necrosis, which is followed by an inflammatory infiltrate and gradually replaced by a fibroblastic reaction.3
In the pre-CT era, the diagnosis was almost exclusively made by laparotomy and the usual treatment was surgical resection of the affected segment. Those patients who did not get operated usually recovered spontaneously.4
Ultrasonography (USG) and CT imaging provide diagnostic information that enables us to confidently rule out any other cause for the patient’s symptoms. Ultrasonography examination generally shows a moderately echogenic, solid, non-compressible, ovoid lesion in the region of maximum tenderness. Real-time USG shows the lesion to be adherent to the peritoneum overlying the anterolateral bowel wall. On CT, the lesion is more circumscribed and shows fat interspersed with hyper attenuating streaks.3
Follow-up scans usually reveal slow but steady disappearance of the abnormalities, which corresponded to the gradual abatement of clinical symptoms, during a period that varied from 4 weeks to 4 months.3
1. Epstein LI, Lempke RE. Primary idiopathic segmental infarction of the greater omentum. Annals of Surgery 1968; 167 : 437-43.
2. Tolenaar PL, Bast TJ. Idiopathic segmental infarction of the greater omentum. Br J Surg 1987; 74 : 1182.
3. Jublin BCM, Puylaert. Right sided segmental infarction of the omentum : clinical, US and CT findings. Radiology 1992; 185 : 169-72.
4. Schnur PL, Mcllrath DC, Carney JA, Whitaker LD. Segmental infarction of the greater omentum. Mayo Clin Proc 1972; 47 : 751-55.
*Fourth Year Resident’ **Associate Professor; ***Third Year Resident, Department of Radiology, LTMM College and LTMG Hospital, Sion, Mumbai 400 022.