Which imaging findings are characteristic of extrathoracic metastasis (M1a)?

Updated: Jan 28, 2019
  • Author: Omar Lababede, MD; Chief Editor: Eugene C Lin, MD  more...
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Answer

The staging CT scan of the thorax is usually extended to include the liver and adrenal glands. CT scanning has a sensitivity of about 85% in the detection of liver metastases. Similar rates may be obtained with MRI and ultrasonography performed by experienced imagers. Ultrasonography is superior to CT scanning in distinguishing metastases from liver cysts, which account for most of the benign lesions seen on CT scans. Adrenal metastases are common and often solitary. They must be differentiated from adrenal adenomas, which occur in 1% of the adult population. Lesions smaller than 1 cm are usually benign. Metastases are usually larger than 3 cm; on nonenhanced CT scans, they have an attenuation coefficient of 10 HU or higher. Adenomas and metastases can also be distinguished by using 3-phase contrast-enhanced CT, MRI, and PET scanning.

MRI is superior to CT scanning in detecting brain metastatic involvement, especially in the depiction of the posterior fossa and the area adjacent to the skull base. PET/CT has low sensitivity for detecting brain metastases involvement, given the presence of a background of high glucose uptake by the normal brain tissue.

Technetium-99m (99mTc) radionuclide bone scanning is indicated in patients with bone pain or local tenderness. The test has 95% sensitivity for the detection of metastases but a high false-positive rate secondary to the increased tracer uptake by the commonly prevalent degenerative disease and posttraumatic changes. The assessment of metastases requires correlation of the bone scans with plain radiographs. Spinal metastases may cause spinal cord compression. Because only about 5% of bony metastases detected with radionuclide scans are asymptomatic, routine preoperative bone scanning is not usually performed. In a 2009 study, PET/CT was superior to bone scan in detecting osseous metastases of non–small cell lung cancer, with a lower incidence of false-positive and false-negative results. [29] . A 2012 meta-analysis reported an overall sensitivity and specificity of 92% and 98%, respectively, for osseus metastases on PET/CT, which was superior to both MRI and bone scan. [30]

Whole body FDG PET/CT is valuable in the evaluation for distant metastasis and can detect clinically unsuspected metastases in up to 25% of patient with non–small cell carcinoma. [31]


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