In
1969 Harkin and Reed described an unusual myxoid tumour of probable nerve
sheath tumour and named it myxoma of nerve sheath. Later in 1980, Gallager
and Helwig described similar lesions as Neurothekeoma. Cellular
neurothekeoma was described by Barnhill and Mihm in 1990.
Variants: 1. Myxoid 2. Cellular
Age: Adolescents and young adults.
Site: Myxoid more common on the trunk and lower extremities and
cellular are more common on the head and neck and upper extremities.
Clinical presentation: Dome shaped nodule less than 3cm in
diameter. Cellular variants are larger and firmer.
1. MYXOID:
Nonencapsulated,
multilobulated and hypocellular tumour , usually located in the reticular
dermis and often extends into the subcutaneous fat.
Tumour is composed of spindle cells, stellate and sometimes epithelioid
cells set in a myxoid stroma.
Spindle cells are arranged in swirling and concentric fashion.
Sometimes multinucleate cells are present.
Focally, there may be nuclear atypia and normal mitotic figures are often
present.
Rarely, foci of ossification and cartilaginous metaplasia have been
reported.
Immunohistochemically the tumour is vimentin and S100 protein positive .
Differential Diagnosis:
Myxoid Soft tissue Tumours.
2. CELLULAR:
Multilobular tumour
composed of nests and fascicles of spindle or epithelioid cells with
vesicular nuclei.
Only focal myxoid change is evident.
Rarely the tumour may demonstrate infiltrative growth pattern, brisk
mitotic activity and cytological pleomorphism. These atypical features do
not influence the prognosis of the tumour.
Immunohistochemically the tumour is S100 protein negative and sometimes
positive to smooth muscle actin and neuron specific enolase . It is
frequently positive to vimentin and melanoma specific antigen (NK1/C-3).
PGP9.5 is positive if antigen retrieval method is used. Differential diagnosis: Spindle cell lesion with atypia and
mitotic activity from head and neck area in an elderly individual, which
stains positively with S100 protein, is more likely to be
Desmoplastic Melanoma.
One should carefully check dermo-epidermal junction. However a
junctional component is not always present in Desmoplastic melanoma.
