IS Case 122: Benign Granular Cell Tumor
Imaging Sciences URMC 2008
Publication Date: 2009-05-20
There is no discrete mammographic abnormality in the area of the patient's palpable inferior breast lump. There is a new hyperdense subcentimeter noncalcified mass in the right upper inner quadrant which demonstrates slightly ill-defined margins on magnification view.
Targeted ultrasound shows a 0.5 x 0.5 x 0.6 cm round hypoechoic mass with an echogenic halo at the 2:00 position 5 cm from the nipple, which corresponds to the new suspicious mammographic mass. This was given a BI-RADS Category 4 (Suspicious Abnormality - Biopsy Should Be Considered). The patient's palpable abnormality was consistent with a sebaceous cyst (not shown).
Granular cell tumors (GCT) are rare benign Schwannian neoplasms. They are more common in females than males and occur most often in the fourth decade of life. Although the majority of these tumors are benign, 1-2% are malignant. However, the differentiation between benign and malignant GCTs is difficult and metastases may be the only indicator of malignancy as the two share similar histologies. Three of six histologic criteria are required to establish malignancy, and include spindling of the tumor cells, the presence of vesicular nuclei with large nucleoli, increased mitotic rate (>/2 mitoses/10 high-power fields at 200x magnification), a high nuclear to cytoplasm ratio, pleomorphism, and necrosis. Also, upregulation of tumor markers p53 and Ki-67 are often but not always observed with malignant GCTs. Clinical features such as size greater than 5 cm, multicentricity, rapid growth, and recurrent disease increase the likelihood of malignant behavior.
The tongue and breast are the most common locations of GCTs, however they also occur in the dermis/subcutis and occasionally are intramuscular. While breast tumors occur predominantly in the upper outer quadrant, granular cell tumors occur most commonly in the upper inner quadrant corresponding to the cutaneous sensory territory of the supraclavicular nerve. Imaging studies usually demonstrate a round/oval and poorly circumscribed mass less than 4 cm. GCT's frequently mimic malignant breast tumors mammographically, appearing as a poorly defined, spiculated mass without internal calcifications. They are equally suspicious on sonography, manifesting as an irregular hypoechoic mass with posterior acoustic shadowing. A minority of lesions may exhibit appear as benign, well-defined rounded masses on mammography and sonography. On CT, they are isodense to muscle and enhance with contrast. On MRI, they are hyper/isointense to muscle on T1-weighted images, isointense on T2-weighted images, and have variable to prominent enhancement on T1-weighted +Gd images. Infiltration, necrosis, or irregular contours suggests a malignant GCT. Treatment consists of local excision and is considered curative, however a wide en bloc excision is required for malignant GCTs.
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