Non-neoplastic pathologies and syndromes
Common acute conditions include epiploic appendagitis, which is inflammation of an omental appendage. On CT, it appears as a small fat-density lesion abutting the bowel wall (most commonly the sigmoid colon) and surrounded by an inflammatory halo. It is characterized by a hyperattenuated rim (hyperattenuated rim), and a central "hyperdense dot" representing a thrombosed vessel is often visible.
Omental infarction occurs when the blood supply to the greater omentum is impaired (primarily due to obesity or secondarily post-surgery). On CT, it appears as a large, heterogeneous mass with dense strands. Its size typically exceeds 5 cm, helping differentiate the process from epiploic appendagitis. Management is predominantly conservative.
Another important imaging pattern is "misty mesentery" (misty mesentery). This is not a standalone diagnosis, but a CT sign of increased attenuation of mesenteric fat. It is caused by edema (in portal hypertension or heart failure), lymphedema, inflammatory processes (pancreatitis, tuberculosis), hemorrhage, or occult neoplasms.
Pathways of tumor dissemination
Primary peritoneal tumors are extremely rare; secondary metastatic lesions are by far the most prevalent. There are four main pathways of spread:
- Direct invasion. Tumors of the stomach, pancreas, and ovaries invade along adjacent ligaments. For example, gastric cancer extends to the colon via the gastrocolic ligament, and retroperitoneal tumors can directly invade the liver via the hepatoduodenal ligament.
- Intraperitoneal seeding. Tumor cells circulate with peritoneal fluid and settle in areas of stasis: the pouch of Douglas, Morison's pouch, and the right paracolic gutter. The result is peritoneal carcinomatosis (peritoneal carcinomatosis). Ovarian cancer (71%), gastric cancer, and colorectal cancer are the most common causes.
- Hematogenous dissemination. Typical for melanoma and breast cancer, foci of which are frequently found on the antimesenteric border of the bowel.
- Lymphogenous spread. The predominant pathway for non-Hodgkin lymphoma.
Specific imaging patterns of tumors
CT and MRI evaluation reveals several specific signs of involvement:
- "Omental cake" sign (omental cake): massive confluent solid infiltration of the greater omentum. Implants show avid contrast enhancement and are well-delineated against the fat tissue.
- Pseudomyxoma peritonei (pseudomyxoma peritonei): occurs upon rupture of mucinous tumors (e.g., of the appendix or ovary). Imaging shows encapsulated low-density mucus collections with septations, forming impressions on the liver capsule (scalloping).
- Mesenchymal carcinoid: characterized by a marked desmoplastic reaction. CT demonstrates radiating fibrous strands, dystrophic calcifications (in 40% of cases), and sharp angulation of bowel loops, which can lead to obstruction.
- "Sandwich" sign (sandwich sign): conglomerate masses of enlarged lymph nodes in non-Hodgkin lymphoma tightly encase mesenteric vessels without causing their occlusion.
Imaging evaluation for surgical treatment
The cornerstone of radical treatment for carcinomatosis is cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC). The role of the radiologist is to evaluate the tumor burden site-by-site for every anatomical region of the abdominal cavity.
The presence of nodes on the small bowel mesentery or extensive infiltration of the hepatoduodenal ligament are critical factors—often absolute contraindications to complete resection. For postoperative monitoring and recurrence detection, routine FDG PET/CT is considered to have low diagnostic accuracy. The gold standards are tumor markers and serial diffusion-weighted MRI (DW-MRI), which detects disease recurrence (especially in appendiceal carcinoma) at the earliest stages.
Briefly: answers to topical questions
Through which peritoneal ligaments does direct tumor invasion occur in gastric and pancreatic cancer?
Direct tumor invasion in gastric and pancreatic cancer occurs along several peritoneal ligaments and the mesentery.
In gastric cancer, the following are involved:
- Gastrosplenic ligament (gastrosplenic ligament) — a pathway of spread to the spleen.
- Gastrocolic ligament (gastrocolic ligament) — a pathway of invasion to the upper margin and anterior surface of the transverse colon.
In pancreatic cancer, the following are involved:
- Hepatoduodenal ligament — a pathway of direct extension into the liver.
- Splenorenal ligament (splenorenal ligament) — a pathway of invasion into the splenic hilum.
- Phrenicocolic ligament (phrenicocolic ligament) — a pathway of spread to the splenic flexure of the colon.
Additionally, pancreatic cancer may spread along the transverse mesocolon (transverse mesocolon) to its inferior margin.
To remember typical sites of cell deposition in peritoneal carcinomatosis, recall fluid accumulation sites: the pouch of Douglas, Morison's pouch, the right paracolic gutter, and the distal mesentery near the ileocecal junction.
Class and exam questions
How to differentiate omental infarction from epiploic appendagitis on CT?
Omental infarction is usually larger than 5 cm and more commonly localized in the right lower quadrant, whereas appendicitis is smaller, closely apposed to the serosal surface of the colon, and features a hyperdense rim with a "hyperdense dot".
What is the essence of the "misty mesentery" sign?
This is a nonspecific CT sign of increased attenuation of mesenteric fat. It arises due to edema, hemorrhage, inflammation, lymphedema, or tumor infiltration.
Why does mesenteric carcinoid frequently cause intestinal obstruction?
The tumor secretes vasoactive substances (serotonin) that provoke an intense desmoplastic reaction. Fibrous strands rigidly fix and deform bowel loops, causing their angulation and stenosis.
What else to study on this topic
- Anatomy of the peritoneal ligamentous apparatus and pathways of direct invasion by gastric and pancreatic carcinomas
- Comparison of MSCT and DW-MRI sensitivity in the diagnosis of peritoneal carcinomatosis
- False-positive signs of carcinomatosis on CT (splenosis, tuberculosis, peritoneal lymphomatosis)
- Impact of desmoplastic reaction in neuroendocrine tumors on CT appearance
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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