Teaching Case

A 51-year-old man complained of sudden onset of right upper quadrant pain and nausea for 1 day. No history of fever, jaundice or injury. He felt no relief on taking analgesics. Routine blood examination along with S. amylase and CECT of the abdomen and pelvis was ordered.

Contrast enhanced axial CT of the abdomen shows a small area of focal fat stranding (Fig. 1a-p) with a characteristic hyperdense peripheral halo sign (Fig. 1f-k and Fig. 2) in the right upper quadrant within the lesser omentum adjacent to the lesser curvature of the stomach. It is seen anterior to gastric antrum and inferior to the left lobe of liver. No CT features of torsion are appreciated.
The pancreatic head, body and tail showed normal attenuation without features of acute pancreatitis. The gall bladder was also within normal limits. No evidence of cholelithiasis or cholecystitis.

Intraperitoneal focal fat infarction (IFFI) includes various entities having the same clinical presentation, imaging features and prognosis [3, 4]. These include infarction in the greater omentum, infarction in the lesser omentum, epiploic appendagitis and diverticulitis. The common pathology in all is the focal fat necrosis [2, 3]. Initial clinical diagnosis depends on the localization of pain and generally concerns appendicitis, cholecystitis, diverticulitis (for epiploic appendagitis) and acute pancreatitis. Hence it mimics any of these conditions [4]. Imaging plays a major role is further decision making regarding patient management [4].
The lesser omentum is formed as the peritoneal reflection between the lesser curvature of stomach and the free edge of the liver. The lesser omentum is made up of fat, lymphatics and vessels [2].
An omental infarction results from vascular compromise of the omentum. Patients may present with sudden onset of abdominal pain, right quadrant pain and tenderness, absence of fever and gastrointestinal symptoms.
Primary omental infarction occurs along the right edge of the omentum where the arterial supply is usually tenuous [1]. Sometimes it is the result from kinking of venous channels. Occasionally omentum twists on itself resulting in omental torsion leading to both arterial and venous compromise. Secondary omental infarction occurs after surgery, abdominal trauma and omental inflammation [1].
Ultrasound will show a focal area of increased echogenicity in the omental fat. CT demonstrates focal area of fat stranding, swirling of omental vessels in omental torsion and hyperdense peripheral halo. Treatment is conservative, however, complications such as abscess formation occur which require surgery or radiological drainage.
As CT increasingly is used for the evaluation of acute abdomen, radiologists are likely to see acute omental infarction and its mimics more often. Recognition of these conditions on CT images will allow appropriate management of acute abdominal pain and may help prevent unnecessary surgery [4].