Metastatic involvement is the most common cause of omental cakes [6]. Along with peritoneal fluid (74%) and peritoneal thickening with enhancement (62%), omental involvement is a frequently encountered finding with peritoneal carcinomatosis on CT [12]. While ovarian carcinoma is the most common cause of omental cakes, colonic, pancreatic, and gastric cancers are other common malignancies that may result in omental metastases [13]. However, virtually any tumour capable of intraperitoneal spread, such as endometrial or bladder cancer, may cause an omental cake (Figs. 4, 5, 6, 7) [13].
Metastases gain access to the greater omentum by any of four principal routes: (1) direct extension of tumour along peritoneal ligaments, (2) intraperitoneal seeding, or via (3) haematogeneous or (4) lymphatic spread of disease [7]. Hepatobiliary malignancies, such as gallbladder carcinoma and cholangiocarcinoma, are unusual causes of omental cakes that often are the result of direct extension of tumour along the hepatoduodenal ligament and lesser omentum (Figs. 8, 9, 10) [7]. Metastatic renal cell carcinoma to the omentum may break through the renal capsule, the anterior renal fascia, and the closely apposed posterior parietal peritoneum to spread along the peritoneal surface [14]. Unusual gynaecologic (fallopian tube and endometrium), genitourinary (prostate and urothelium), small bowel, and appendiceal primary cancers also may result in intraperitoneal seeding (Figs. 11, 12, 13, 14). Melanoma, lung, and breast cancers can cause omental cakes, typically by haematogenous spread. Metastases from breast cancer to the stomach may extend directly into the greater omentum (Figs. 15 and 16). Non-Hodgkin’s lymphoma, and, very rarely, Hodgkin’s disease, can develop omental cakes, often with associated diffuse peritoneal and retroperitoneal disease, and ascites from lymphatic spread (Fig. 17) [15].
With regards to imaging findings, obvious careful search for the primary malignancy is important to determine the aetiology if the cause of the omental cake is unknown. Metastatic omental involvement occasionally may be heralded by abdominal pain secondary to bowel obstruction or intussusception in cases of gastrointestinal malignancies that metastasise to the small bowel.
Primary malignancies and benign tumours of the peritoneum and omentum are rare. Typically of mesenchymal origin, they include: abdominal mesothelioma, haemangiopericytoma, leiomyoma, leiomyosarcoma, gastrointestinal stromal tumour (GIST), lipoma, liposarcoma, neurofibroma, fibrosarcoma, and small round cell tumours (Figs. 18, 19, 20, 21) [16, 17]. While these primary lesions are rare, these should be considered in the absence of a known or suspected primary organ-based malignancy [17]. With respect to differentiating imaging findings for benign versus malignant neoplastic cakes, benign lesions usually are well circumscribed, while malignant cakes commonly have indistinct margins and invade surrounding structures [13].