DIFFERENTIATION BETWEEN MULTIPLE LIVER HEMANGIOMAS AND LIVER METASTASES OF GASTRINOMAS - VALUE OF ENHANCED MRI

Purpose: Hepatic metastases of neuroendocrine tumors are known to mimi c hemangiomas on nonenhanced SE MR sequences. The usefulness of MR exa mination with gadolinium injection to identify lesions was prospective ly evaluated. Method: Nine patients with multiple liver metastases of gastrinomas were compared with six patients showing multiple liver hem angiomas. Patients underwent unenhanced T2-weighted SE, T1-weighted SE , and FLASH sequences, followed by enhanced sequential FLASH sequences and a 5 min delayed T1-weighted SE sequence. Results: On T2-weighted SE sequence, all hemangiomas displayed the same typical morphology as a sharply defined, homogeneous, high signal intensity lesion, but this pattern was also observed for some or all of the lesions in seven of nine patients with gastrinoma metastases. Dynamic FLASH sequences were accurate for lesions larger than 2 cm, hemangiomas displaying a nodul ar peripheral enhancement with centripetal filling in, and metastases displaying either an initial homogeneous or a regular peripheral enhan cement. Precise assessment of lesions smaller than 2 cm remained equiv ocal. Delayed T1-weighted SE sequence (performed at least 5 min after Gd-chelate injection) was the most accurate technique to identify meta stases by showing hypo- or isointensity signal, whereas all hemangioma s were hyperintense. Conclusion: Postcontrast delayed T1-weighted sequ ence is the primary technique to differentiate equivocal cases of hema ngiomas from metastases of gastrinoma.