Case

Routine breast screening examination in an asymptomatic 61-year-old female patient revealed a suspicious lesion in the axillary tail of the right breast. There was no history of breast cancer. Mammography showed a dense, spiculated mass at the upper outer quadrant of right left breast (Figure 1, arrow). Ultrasound demonstrated an irregular delineated hypoechoic lesion. There was a subtle partial hyperechogenic halo (Figure 2, arrow) and marked posterior acoustic shadowing (Figure 2, arrowhead). No pathological axillary lymph nodes were found. On magnetic resonance imaging (MRI), the lesion had spicular margins and avid, homogenous contrast enhancement on T1-weighted images (WI) (Figure 3, arrow). Histopathology confirmed the diagnosis of a granular cell tumor of the breast.

Comment

Granular cell tumors (GrCT) are rare tumors of neural origin with Schwannian differentiation. Typically, a GrCT has abundant granular eosinophilic cytoplasm on microscopy, from which the tumor derives its name. A GrCT can occur in all soft tissues and has a prevalence of 6.7:1000 in the population undergoing evaluation for breast cancer. While mostly benign, malignancy has been reported in 0.5%–2.0% of cases.

Clinically, a GrCT is a solitary and painless mass that may be identified on palpation. On mammography, a GrCT can present as a benign-looking, well-defined nodule or show features suggestive of malignancy such as irregular margins, spiculation, and architectural distortion. Calcifications are generally absent.

Similar to mammography, on ultrasound a GrCT can appear as a well-circumscribed solid nodule or as an ill-defined heterogenic mass with variable vascularization. Sometimes a hyperechogenic halo may be seen, and posterior acoustic shadowing may be present depending upon the degree of reactive fibrosis. The most specific feature is the presence of anisotropy. A degree of variable echogenicity, depending on the angle of the insonating beam, may be seen due to the internal fibrillary composition. On MRI, a GrCT is of low to intermediate signal intensity on T1-WI but is often inconspicuous on T2-WI. Enhancement is variable after administration of gadolinium contrast. Both progressive (type 1) and wash-out (type 3) dynamic curves have been described. Additionally, a GrCT does not have increased metabolic activity on PET-CT; this feature can be helpful to differentiate a GrCT from malignancy.

Due to the non-specific imaging findings, tissue analysis is required for definite diagnosis.

While the prognosis of a GrCT is generally good, metastatic disease has been described. The recommended treatment is wide surgical excision considering the higher risk of recurrence with positive resection margins [1].