Breast MRI in the Evaluation of Patients with Occult Primary Breast Carcinoma

Occult primary breast carcinoma presenting as isolated ipsilateral axillary lymph node metastases in patients with normal mammograms and normal physical exams accounts for less than 1% of all breast carcinomas. Contrast-enhanced magnetic resonance imaging (MRI) may identify the site of primary breast carcinoma and effect management of these patients. We report on eight consecutive women evaluated in our multidisciplinary clinic who had biopsy-proven metastatic adenocarcinomas to axillary lymph nodes and occult primary carcinomas. Each patient underwent MRI at 1.5 T with a volumetric fast-spoiled gradient-echo (3D FSPGR) pulse sequence before and after injection of gadopentetate dimeglumine. Wire localization of suspicious areas of enhancement was performed under MRI or mammography guidance followed by surgical excision. Seven (88%) of the eight normal mammograms showed dense (>50%) breast parenchyma. In two (25%) of the eight patients, suspicious focal or regional enhancement was seen on MRI. Following wire localization and excision, pathologic exam showed an invasive ductal carcinoma and ductal carcinoma in situ with invasion corresponding to the MRI enhancement in the two cases. Breast MRI can identify the primary tumor site and influence management of patients presenting with clinically and mammographically occult primary breast carcinomas.