False-positive hepatic blood pool scintigraphy in metastatic colon carcinoma.

A rare false-positive red blood cell scintigram occurred in a 49-year-old woman with two metastases from a primary adenocarcinoma of the sigmoid colon. Although the blood flow and static planar images were unremarkable, a 1-hour postinjection SPECT study showed a focus of increased activity in the inferior right lobe and a second photopenic focus in the dome. Following a trisegmentectomy, pathologic examination revealed the two metastases with no evidence of a hepatic hemangioma. Microscopy, however, showed a discrete area of nonspecific reactive changes (focal sinusoidal dilation and congestion) immediately adjacent to teh metastasis in the inferior right lobe. It is postulated that the SPECT focus of increased activity occurred secondary to the labeled blood pool within the area of sinusoidal dilation, rather than within the adjacent metastasis.