Glomus tumor of uncertain malignant potential of the brachial plexus: A case report

Table 1 Classification of atypical glomus tumors[1,2]

Atypical glomus tumors	WHO 4th edition (2013)	Enzinger and Weiss’s Soft Tissue Tumors. 6th edition (2014)
Malignant glomus tumor	(1) Marked nuclear atypia and any level of mitotic activity; or (2) Atypical mitotic figures	(1) Marked atypia + mitotic activity (> 5/50 HPF); or (2) Atypical mitotic figures
Glomus tumors of uncertain malignant potential	Not fulfilling criteria for malignancy, but having at least one atypical feature other than nuclear pleomorphism	(1) Superficial location + mitotic activity (> 5/50 HPF); or (2) Large size (> 2 cm) and/or deep location
Symplastic glomus tumor	Striking nuclear atypia in the absence of any other features indicative of negative outcome (e.g., large size, deep location, mitotic activity, necrosis)	Lack criteria for malignant glomus tumor and marked nuclear atypia only

HPF: High power field; WHO: World Health Organization.

Table 2 Differential diagnosis of atypical glomus tumors[4]

Superficial lesion	Deep lesion
Merkel cell carcinoma	Hemangiopericytoma
Eccrine spiradenoma	Leiomyosarcoma with epithelioid change
Melanoma	Rhabdomyosarcoma
Ewing sarcoma/PNET	Ewing sarcoma/PNET
Neuroblastoma

PNET: Primitive neuroectodermal tumor.