Metastases on a CT scan: lung, liver, bone and peritoneum

When a report says “metastases,” “secondary lesions,” “implants,” “nodules” or “suspicious lesions,” the useful question is not just whether the word sounds serious. A proper review asks where the finding is, what pattern it has, what primary cancer is known, what changed and what information is still missing.

First: what metastasis means

Metastasis means tumor cells separated from the place where they started and reached another part of the body through blood vessels, lymphatic channels, direct extension or seeding within cavities. The origin still matters. If breast cancer reaches the lung, it is interpreted differently from a primary lung cancer.

That is why an oncology CT scan is not read as a random list of spots. It is read with a clinical question: what tumor is known, where does it usually spread, what is new, what is stable and what else could explain the finding?

Why CT is so useful in oncology

CT can evaluate the chest, abdomen, pelvis, lymph nodes and bones in one examination, with strong anatomic detail. It is useful for staging, comparing treatment response, detecting complications and deciding whether another test is needed, such as MRI, PET/CT, targeted ultrasound or biopsy.

Intravenous contrast may be important, especially for the liver, abdomen and vessels. A non-contrast scan can answer some questions, but others may remain limited. A serious interpretation should state that limitation clearly.

Sites reviewed systematically

Lung: nodules, mass or pleural fluid

The lung is a common metastatic site. On CT, the review checks whether nodules are present, their size, margins, density, distribution, whether they are solid or subsolid, whether they calcify or cavitate, and whether they grew. A small isolated nodule does not automatically mean metastasis; it may be a scar, granuloma, infection or incidental finding.

The finding becomes stronger when several pieces fit together: multiple new nodules, progressive growth, distribution compatible with the primary cancer or additional signs of disease elsewhere.

Liver: focal lesions and contrast pattern

In the liver, it is not enough to say “there is a lesion.” A radiology review evaluates whether the lesion is low attenuation, hypervascular, rim-enhancing, cystic, hemangioma-like or otherwise benign-appearing, and in which contrast phase it is best seen. Many liver metastases are hypovascular and are best seen in the portal venous phase, but some tumors produce hypervascular lesions.

A common mistake is treating any liver lesion as a metastasis. Benign liver lesions are very common. Enhancement pattern, number of lesions, cancer history, prior imaging and sometimes liver MRI matter.

Peritoneum: implants, ascites and omentum

The peritoneum lines the abdominal cavity. When peritoneal disease is present, CT may show ascites, small nodules, peritoneal thickening, implants, mesenteric involvement or omental disease. Some reports use the phrase “omental cake,” which describes tumor-like thickening of the omentum, although the appearance is not specific to one cause.

Colon, ovarian, stomach, pancreatic and other cancers may involve the peritoneum. Infections or inflammatory diseases may sometimes mimic it. Imaging must be interpreted with symptoms, labs, history and, when needed, tissue sampling.

Bone: lytic, sclerotic or mixed lesions

CT shows cortical and trabecular bone detail very well. Some metastases destroy bone and are described as lytic. Others increase density and are described as sclerotic or blastic. Mixed patterns can occur.

The pattern relates to the primary tumor, but it is not an absolute rule. After treatment, sclerosis may also represent healing response; that should not be called progression automatically without comparing dates and evolution.

Report words: how to read them without panic

Information that helps a second reading

• the main question: “could this be metastasis?”, “did it grow?”, “are there more lesions?”, “which organ is concerning?”;
• known cancer type, if any, and treatments received;
• exact CT date and whether it was with contrast, without contrast or both;
• previous report, prior studies and comparisons;
• complete images in a viewer/PACS, not screenshots only;
• important symptoms, surgeries, infections or recent biopsies.

When is another reading worth it?

It is worth considering when report wording may affect decisions, when two opinions differ, when prior studies need careful comparison, when the patient does not understand which organ is involved, or when the clinical question was not clearly answered. A good second reading does not simply repeat the report: it organizes the problem.