55 Intramammary Spindle-Cell Lesions: Imaging–Pathology Correlation

Background

Low-grade/bland-looking intramammary spindle-cell lesions can mimic both benign and malignant breast masses on imaging. Their differential diagnoses include benign, reactive, and malignant entities. Understanding their typical imaging appearance and pathologic features can help radiologists narrow the differential diagnosis and avoid unnecessary aggressive treatment. They typically present as palpable masses or incidental findings on imaging. Low-grade spindle cell lesions may be biphasic (with epithelial component) or monophasic (containing no epithelial components). Here, we review monophasic lesions containing bland-looking spindle cells only.

Materials and Methods

We retrospectively reviewed 5 intramammary spindle-cell lesions with histologic confirmation at a single institution, including 2 schwannomas, 1 spindle-cell lipoma, 1 mammary myofibroblastoma, and 1 spindle-cell neoplasm not otherwise specified. For each case, mammography, ultrasound, and, when available, MRI were evaluated for lesion detectability, morphology, margins, echotexture, and enhancement pattern. Final pathology reports were reviewed to document the specific diagnosis and to assess radiologic–pathologic concordance and subsequent management.

Results

When visible on mammography, lesions appeared as circumscribed oval or round masses without suspicious calcifications, or as a focal asymmetry without associated features. Ultrasound demonstrated solid, circumscribed masses in all evaluable cases, most of which were hypoechoic; the spindle-cell lipoma was characteristically hyperechoic. Internal echotexture ranged from homogeneous to mildly heterogeneous, without frankly infiltrative borders or overt architectural distortion. MRI, when performed, demonstrated an enhancing mass with benign or indeterminate kinetic patterns rather than classic malignant washout. All lesions had benign or low-grade spindle-cell diagnoses on pathology, and no lesion was upgraded to high-grade malignancy on final histology. Management consisted of image-guided core needle biopsy only; no surgical excision was performed in this series, and there was no radiologic–pathologic discordance.

Conclusions

Intramammary spindle-cell lesions such as schwannoma, spindle-cell lipoma, mammary myofibroblastoma, and related spindle-cell neoplasms may raise initial concern for malignancy because they present as solid breast masses, yet they often demonstrate circumscribed morphology, lack calcifications, and show benign or only mildly suspicious features across modalities. Careful radiologic–pathologic correlation and awareness of these entities can support a confident benign diagnosis after biopsy, reduce diagnostic uncertainty with respect to spindle-cell metaplastic carcinoma, and help avoid unnecessary surgery in appropriately concordant cases.