Glomus cells show immunohistochemical features of modified smooth muscle cells.
Parameters:
(1) location (superficial to muscular fascia or deep to it, page 2 column 1)
(2) size
(3) mitotic rate per high power field (400x total magnification, microscopic field area not stated)
(4) mitotic figures
(5) nuclear atypia/grade (low, moderate or high)
(6) growth pattern
Classification:
(1) malignant glomus tumor ("glomangiosarcoma")
(2) symplastic glomus tumor (glomus tumor with nuclear atypia)
(3) glomus tumor of uncertain malignant potential
(4) glomangiomatosis
(5) benign glomus tumor
Malignant glomus tumor - one or more of the following criteria:
(1) large size (>= 2 cm) AND deep location
(2) atypical mitotic figures
(3) high nuclear grade (marked nuclear atypia) AND high mitotic activity (>= 5 per 50 high power fields)
Symplastic glomus tumor - all of the following:
(1) high nuclear grade (marked atypia)
(2) mitotic rate < 5 per 50 high power fields
(3) does not meet other criteria for malignancy
Glomus tumor of uncertain malignant potential - one or more of the following:
(1) superficial location AND high mitotic activity (>= 5 per 50 high power fields)
(2) large size (>= 2 cm) only
(3) deep location only
Glomangiomatosis - both of the following:
(1) does not meet criteria for malignant glomus tumor, symplastic glomus tumor, or glomus tumor of uncertain malignant potential
(2) diffuse growth with excess glomus cells, resembling angiomatosis
Benign glomus tumor: none of the above
