“A 49 y/o Woman with a Large
Thigh Mass”
California Tumor Tissue Registry’s
Case of the Month
CTTR COTM Vol 14:1
www.cttr.org
October, 2011
A 49 year-old woman presented with a left thigh mass. It was completely excised and
found to be well circumbscribed. It weighed 13 grams, and was relatively homogeneous
gray-to-tan. It lacked hemorrhage and/or necrosis.
Microscopically, the tumor had well-defined border (Figs. 1&2) and grew in a whorled
lobular or “finger print” pattern (Fig. 3). High density regions of cells were
juxtapositioned with lowly cellularity regions (Fig. 4). The cells were polygonal,
epithelioid and spindled, with intervening collagen (Fig. 5). The nuclei were bland, and
lacked pleomorphism or significant mitotic activity (Fig. 6).
Immunohistochemistry showed strong S100 positivity and negative staining for
cytokeratin.
Diagnosis: Cellular neurothekeoma, thigh
Michelle Iverson, PSF, and Donald R. Chase, MD
Department of Pathology and Human Anatomy, Loma Linda University and
Medical Center, Loma Linda, California
California Tumor Tissue Registry, Loma Linda, California
Neurothekeoma (NT) is a term used by Gallager and Helwig in 1980 to reference a
unique neural tumor. As described, NT is a superficial dermal tumor that typically occurs
in the upper extremities of the head and neck, mostly in the first two decades of life. It is
comprised of epithelioid cells and spindle cells which arrange into nodules with a
whorled or somewhat spiral fascicular pattern. Collagen is often seen in association with
the cellularity. Nuclear atypia and mitotic figures are rare, and when they do occur, the
clinical significance is uncertain. Treatment consists of excision and clinical monitoring.
The tumors are considered low-grade without metastatic potential, although local
reoccurrence has been described.
Rosati, in 1986, described a cellular variant of myxoid neurothekeoma. This variant
appears morphologically the same as classic neurothekeomas, however the
immunohistochemical profile is shows S100 is be negative and NKI-C3 and NSE to be
positive.
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Although the tumor can usually be diagnosed on its unique growth patterns, mimickers
include:

Nerve sheath myxoma which has a greater myxoid component, and is multilobular
with a prominent fibrous periphery. The cells are more spindled and stellate.
They are S100 and GFAP positive.

Melanocytic neoplasms (especially Spitz nevus) show downward growth which is
not seen in cellular neurothekeoma. They show epithelioid and spindle cells in a
nested pattern.

Plexiform fibrohistiocytic tumor is a multinodular, biphasic tumor composed of
histiocytic cells and osteoclast-like giant cells with fascicles of fibroblastic cells
in-between.
Suggested reading:
Hornick, JL, Fletcher, CDM. Cellular neurothekeoma: detailed characterization in a
Series of 133 cases. Am J Surg Pathol 2007; 31:329.
Barnhill, R.L., Mihm M.C. Jr. Cellular neurothekeoma: a distinctive variant of
neurothekeoma mimicking nevomelanocytic tumors. Am J Surg Pathol 1990; 14:113.
Calonie, E., Wilson Jones, E., Smith N.P. Cellular ‘neurothekeoma’; an epitheloid
variant of pilar leiomyoma? Morphological and immunohistochemical analysis of a
series. Histopathology 1992; 20:397.
Fetsch, JF, et al. Neurothekeoma: an analysis of 178 tumors with detailed
immunohistochemical data and long-term patient follow-up information. Am J Surg
Pathol 2007; 31:1103.
Gallager, R.L., Helwig, E.B. Neurothekeoma-benign cutaneous tumour of neural origins.
Am J Clin Pathol 1980; 74:759.
Fetsch, JF, et al. Nerve sheath myxoma: a clinicopathologic and immunohistochemical
analysis of 57 morphologically distinctive, S-100 protein- and GFAP-positive, myxoid
peripheral nerve sheath tumors with a predilection for extremities and a high local
recurrence rate. Am J Surg Pathol 2005; 29:1615.
Angervall, L., Kindblom, L-G., Haglid, K. Dermal nerve sheath myxoma. A light and
electron microscopic, histochemical and immunohistochemical study. Cancer 1984;
53:1752.
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