Desmoid tumor, also known as fibromatosis of the breast, is a rare benign entity, accounting for only 0.2 % of all breast tumors. It is characterized by low-grade, uniform spindle-cell proliferation carrying no malignant potential, but it has shown a significant risk for local recurrence. Therefore, the current management of desmoid tumors is wide excision with clear margins. The mammographic and sonographic features mimic those of malignancy. On MR imaging, a desmoid tumor can appear as an ill-defined or circumscribed mass with low to intermediate signal intensity on the T1-weighted images and increased signal on the T2-weighted images. Progressive enhancement kinetics is usually seen on dynamic contrast imaging. Although these imaging features are nonspecific, MRI can be useful to show chest wall involvement important for surgical planning.

Pheochromocytomas are an uncommon tumor of the adrenal gland. The tumors generally follow a 10 % rule:

Primary breast amyloidosis is rare, and breast involvement is usually part of the systemic disease. Similar to amyloid deposits elsewhere in the body, calcifications can develop in the breast. Mammographic features of breast amyloidosis include irregular or circumscribed masses with coarse, dystrophic calcifications (Fig. 5.5). On MRI examination, lesions generally demonstrate decreased T1 signal intensity with associated increased T2 signal corresponding with edema and inflammation. Delayed progressive enhancement pattern is usually noted on the post-contrast images. Core biopsy is recommended in most cases of indeterminate findings to confidently exclude co-existent malignancy.