Peritoneal cancer involves the peritoneum, the thin membrane lining the abdominal and pelvic cavities and covering most of the organs within them. This cancer is often secondary, spreading from a primary tumor in an organ like the ovaries, colon, or stomach, though it can also originate there as primary peritoneal cancer. Because early-stage symptoms are often vague, imaging plays a prominent role in evaluating the extent of the disease. Computed Tomography (CT) scanning is the primary method used to detect and evaluate this cancer due to its availability and comprehensive imaging capabilities.
How Computed Tomography Aids Initial Diagnosis
Computed Tomography is the first-line imaging tool used when peritoneal cancer is suspected, providing rapid, cross-sectional images of the entire abdomen and pelvis. The CT scan uses specialized X-ray technology to create detailed pictures, helping doctors assess if cancer is present and how far it has spread. Standard protocols involve scanning the chest, abdomen, and pelvis, often using intravenous contrast dye to highlight tissues and blood vessels.
The utility of CT imaging lies in its ability to quickly map the disease burden, which is a factor in treatment planning. By providing a three-dimensional view, doctors can identify masses, determine the relationship of suspicious lesions to major organs, and evaluate lymph nodes. This initial assessment is crucial for staging the cancer, which determines the appropriate course of action, such as surgery or chemotherapy.
CT scans are effective at identifying larger tumors and extensive disease involvement. The scan is a practical tool for patients experiencing symptoms like abdominal pain or swelling. While it does not provide a definitive diagnosis—which requires a tissue biopsy—the CT scan establishes a strong suspicion of peritoneal malignancy and guides the next diagnostic steps.
Visual Markers of Peritoneal Cancer on the Scan
Peritoneal cancer manifests on a CT scan through several visual markers. One frequent finding is ascites, which is an abnormal accumulation of fluid in the abdominal cavity. Ascites is found in many cases and indicates that further, more specific testing is warranted.
The tumors often appear as peritoneal nodules or implants, which are small masses located on the lining of the abdomen. These implants are solid lesions with variable enhancement after contrast injection. When these nodules become numerous, they can cause a thickening of the parietal peritoneum, making the lining visible as an enhancing thin line along the abdominal wall.
Another common sign is “omental caking,” which indicates extensive tumor involvement of the omentum. The omentum is a fatty, apron-like structure that, when infiltrated by cancer, becomes thickened and appears nodular or mass-like on the CT image. Additionally, the cancer can affect the intestines, leading to signs such as bowel wall thickening or irregularities.
When CT Imaging Requires Further Confirmation
Despite its strengths, the CT scan has limitations in its ability to detect the full extent of peritoneal cancer, particularly very small disease deposits. The sensitivity of CT significantly decreases when trying to visualize peritoneal implants less than one centimeter in diameter. For lesions smaller than five millimeters, the sensitivity can drop to as low as 11%, meaning many microscopic or subtle tumors may be missed.
This challenge is compounded by the anatomy of the peritoneum, where small implants can hide in complex regions such as the root of the mesentery, the lesser omentum, or the surface of the small bowel. The diffuse and scattered nature of peritoneal cancer, rather than a single large mass, makes it inherently difficult for any single imaging modality to capture every deposit. Therefore, an accurate assessment of the total disease burden often requires supplementary testing.
Complementary Imaging Modalities
To overcome the CT scan’s shortcomings, doctors frequently employ complementary modalities like Magnetic Resonance Imaging (MRI) or Positron Emission Tomography (PET) scans. MRI, particularly with diffusion-weighted sequences, offers superior soft tissue contrast and is often more sensitive than CT for detecting small lesions, especially in difficult anatomical areas. PET scans are useful for assessing the metabolic activity of tumors and detecting spread outside the abdomen, though they can struggle with some low-activity tumors.
Definitive Diagnosis
Ultimately, the definitive diagnosis and the most accurate determination of the disease extent rely on tissue sampling or direct visualization. A biopsy, which involves taking a small sample of the suspicious tissue, is required for confirmation of malignancy. For the most precise staging, a diagnostic laparoscopy, a minimally invasive surgical procedure, may be performed to directly visualize the entire peritoneal surface and confirm the findings suggested by the CT scan.