What can a CT scan show in a case of suspected metastatic disease?

What a CT Scan Shows in Suspected Metastatic Disease

A CT scan with IV contrast is the primary imaging tool for detecting metastatic disease, revealing enlarged lymph nodes (>1 cm), lung nodules, liver lesions, bone destruction, and abnormal masses in organs like the adrenal glands—with contrast enhancement being critical to distinguish malignant from benign findings with 74-77% accuracy. 1

Primary Findings CT Detects

Lymph Node Metastases

• Enlarged lymph nodes greater than 1 cm in shortest axis are highly suspicious for metastatic disease, particularly in anatomically relevant "landing zones" for specific cancers 2
• CT detects metastatic lymph nodes with 65-96% sensitivity and 81-100% specificity, though accuracy declines with limited disease 2
• Up to 60% of metastatic lymph nodes can be smaller than 1 cm, which is why some radiologists use a 0.7-0.8 cm cutoff at the expense of more false positives 2
• IV contrast improves detection by distinguishing nodes from adjacent blood vessels 2

Lung Metastases

• CT chest is far superior to chest X-ray for detecting lung metastases, with chest X-ray missing up to 72% of metastases that CT identifies 2
• The lungs are the most common site of distant metastases for many cancers, occurring in up to 90% of cases with distant spread 2
• Small pulmonary nodules ranging from 0.2 to 1.5 cm can be detected on CT but are invisible on chest X-rays 3
• CT identifies both the size and number of nodules, which helps distinguish metastases from benign findings over time 4

Liver Metastases

• Contrast-enhanced CT achieves 77-95% sensitivity for detecting liver metastases, compared to only 61-100% for non-contrast CT 1
• Hypovascular metastases appear as darker (hypoenhancing) lesions best seen during the portal venous phase of contrast imaging 1
• Hypervascular metastases require arterial phase imaging, as up to 59% may be invisible on single-phase scans 1
• Isolated liver masses require biopsy to confirm metastatic disease if the patient is otherwise potentially curable 2

Bone Metastases

• CT can detect bone destruction and lytic lesions in ribs, spine, and other skeletal structures 5
• CT clearly demonstrates subtle or complete segmental bone destruction and can show accompanying soft tissue masses 5
• Bone metastases often occur alongside lung or mediastinal metastases rather than in isolation 6

Adrenal Gland Involvement

• Any isolated adrenal mass found on CT requires biopsy to rule out metastatic disease in potentially resectable patients 2
• Delayed contrast-enhanced CT (15-30 minutes post-contrast) can distinguish benign adenomas from metastases with >95% sensitivity and >97% specificity 1

How Contrast Enhancement Helps

• IV contrast is essential because it differentiates malignant from benign lesions with 74-77% accuracy, compared to significantly lower accuracy without contrast 1
• Contrast helps identify abnormal blood flow patterns—metastases often enhance differently than normal tissue 1
• Without contrast, CT cannot reliably distinguish lymph nodes from adjacent blood vessels or small bowel loops, reducing sensitivity 2
• Contrast aids in detecting mediastinal and hilar adenopathy by making nodes stand out from vessels 2, 7

Common Incidental Findings

• 91% of patients with sarcoma have at least one abnormal finding on staging CT scans 4
• Indeterminate lung nodules appear in 33% of patients, but only 31% of these prove to be true metastases on follow-up 4
• Primary tumor size ≥14 cm significantly increases the likelihood that indeterminate nodules represent true metastases (odds ratio 16.6) 4
• Most abnormal findings require surveillance imaging rather than immediate intervention, as the majority are not metastatic 4

Extent of CT Coverage

• CT chest should extend inferiorly to include the liver and adrenal glands to screen for metastases in these common sites 2
• For advanced disease (stage IB2 or greater), the rate of occult metastases can be as high as 38%, making thorough imaging critical 2, 7
• CT abdomen and pelvis adds value for detecting retroperitoneal lymph nodes, peritoneal disease, and pelvic organ involvement 2

Limitations to Understand

• CT cannot detect metastatic disease in normal-sized lymph nodes, which is why 40-60% of metastatic nodes may be missed 2
• Inflammatory or reactive lymph nodes cannot be reliably distinguished from metastatic nodes based on size alone 2
• Young patients with little retroperitoneal fat may have suboptimal CT imaging of abdominal lymph nodes 2
• Non-contrast CT provides very poor soft tissue characterization in the pelvis and abdomen, making it inadequate for comprehensive metastatic evaluation 2