Cellular neurothekeoma

(Greek theke, sheath)

Definition

A dermal/subcutaneous tumour of uncertain histogenesis. At one time considered the cellular equivalent of dermal nerve sheath myxoma, these two entities are not longer considered to be related. The mixed-type variant of neurothekeoma has a myxoid component but should be classified with other neurothekeomas.

Epidemiology

This tumour may occur at any age, including in children, with most cases occurring before the age of 40 years. There is a female predominance.

Clinical features

Presentation is usually with a painless mass. Tumours most commonly occur on the upper extremity (particularly shoulder), followed by the head (particularly face) and neck, lower limbs and trunk.

Macroscopic appearance

The mean tumour size is 1 cm and most are smaller than 2 cm.

Histopathology

All tumours have a dermal component and about half extend into the subcutis. The margins are ill-defined and may infiltrate fat or skeletal muscle. A Grenz zone separates the tumour from the epidermis. The tumour is lobulated or micronodular. A few cases are plexiform. It is composed of nests of cells which vary from epithelioid to spindled with pale cytoplasm. The cells may be surrounded by dense collagen. Some cases have a myxoid stroma, of variable extent. Nuclear pleomorphism is usually mild but a minority of cases include markedly atypical cells. Mitotic figures average 3 per 10 HPF. A minority of cases have Touton or osteoclast-like giant cells.

Immunohistochemistry

 

NKI-C3

133/1331, 9/113

 

NSE

110/1231, 0/124

SMA

73/1271, 1/124

Desmin

1/1151, 0/124

S-100

0/1331, 0/113 , 3/124

S100A6

7/72

PGP9.5

3/72, 12/123

Microphthalmia transcription factor

9/113

GFAP

negative1

MART-1

negative1

Leu-7

0/124

Synaptophysin

0/124

EMA

1/124

Vimentin

12/124

   
   

Ultrastructure

Specific features are lacking, the cells appearing to be myofibroblastic.

Differential diagnosis

Prognosis

Cellular neurothekeomas are benign tumours that do not recur, even when incompletely excised. Cytological atypia does not seem to be of prognostic significance.

References

1 Hornick JL,Fletcher CD. Cellular neurothekeoma: detailed characterization in a series of 133 cases. Am J Surg Pathol 2007; 31:329-40

2 Fullen DR, Lowe L,Su LD. Antibody to S100a6 protein is a sensitive immunohistochemical marker for neurothekeoma. J Cutan Pathol 2003; 30:118-22 FULL TEXT

3 Page RN, King R, Mihm MC, Jr., et al. Microphthalmia transcription factor and NKI/C3 expression in cellular neurothekeoma. Mod Pathol 2004; 17:230-4 FULL TEXT

4 Wang AR, May D, Bourne P, et al. PGP9.5: a marker for cellular neurothekeoma. Am J Surg Pathol 1999; 23:1401-7

This page last revised 9.6.2007.

©SMUHT/PW Bishop