Glomus tumor is an uncommon benign tumor usually presenting with a small mass occurring in the dermis or soft tissue of an extremity, especially subungual region. However, intraneural glomus tumor is sporadic. While most of the glomus tumors are benign, atypical glomus tumors with unusual features can be occasionally found, leading to distinctive malignant potential required different therapeutic approaches. Glomus tumor of uncertain malignant potential is one type of atypical glomus tumor with limited criteria for malignancy and without metastasis.
Herein, we report a case of a 48-year-old Thai male with a large painful mass in his axilla for one year without apparent neurological deficit. Magnetic resonance imaging showed a large heterogeneous mass encasing entire posterior cord of left brachial plexus and axillary artery. The tumor tissue from core needle biopsy histologically demonstrated the sheets and cords of relatively uniform tumor cells with foamy cytoplasm and round to oval hyperchromatic nuclei without atypia. The mitotic count was 0 per 50 high power field. A final diagnosis of glomus tumor of uncertain malignant potential was rendered. Complete surgical resection was performed, followed by adjuvant radiation due to positive margin. Neither local recurrence nor distant metastasis was observed at 2-year follow up. Unfortunately, postoperative incomplete brachial plexopathy without signs of re-innervation by electromyography was persisted. Later nerve grafting reconstruction was performed, followed by ongoing neurological rehabilitation.
Glomus tumor of uncertain malignant potential is exceedingly rare, especially around brachial plexus. Although the prognosis is good, careful histological diagnosis and treatment are needed to achieve an optimal outcome with lower morbidity.