CTTR S Case of the Month

“A 59 Year Old Man With A Mass In His Hand”

CTTR’s Case of the Month

May, 2003

A 59-year-old male with a gradually enlarging left hand mass had an MRI 1 1/2 year previous which was interpreted as being consistent with an intramuscular lipoma. An x-ray shortly before resection showed a 3.5 cm mass with calcifications. There was no bone or joint involvement.

The excised specimen was 15 grams, 3.5 x 3.0 x 2.3 cm, pink-tan, ovoid and firm. A well-circumscribed, glistening capsule was present. The cut surface showed areas of calcification which microscopically consisted of a thin, focal rim of lamellar bone (Fig. 1).

Some regions of the tumor were quite fibrous and contained round, oval, or spindled cells arranged in nests or cords (Fig 2a). A subtle blending of fibrous and myxomatous regions was seen (Fig 2b).

The more cellular regions contained uniform cells in a variably myxomatous stroma. Some cells demonstrated perinuclear clearing (Fig. 3a). There were also areas that were hypocellular and densely fibrous (Fig. 3b).

Myxomatous regions were microcystic (Fig. 4a) or diffuse (Fig. 4b).

Electron microscopy of a similar tumor showed perinuclear accumulations of intermediate filaments (Fig. 5a), as well as a thick external lamina which covered part of the cell body (Fig. 5b) (See Acknowledgement).

Diagnosis:

Ossifying Fibromyxoid Tumor of Soft Tissue (OFMT)

Sajjad P. Syed, M.D. and Donald R. Chase, M.D.

Loma Linda University and Medical Center, Loma Linda, California

First described in 1989, ossifying fibromyxoid tumor (OFMT) is a rare tumor of uncertain derivation. It usually presents as a small, painless mass in the extremities, but also has also been reported in the trunk, head & neck, mediastinum, retroperitoneum, nasal cavity, and paraspinal regions. Imaging studies are of a solid, well circumscribed mass showing areas of calcification, usually around the periphery.

On gross examination, OFMT appears well circumscribed, lobulated or multinodular, and usually has a tan-white, gritty surface. Microscopy shows the tumor to consist of uniform cells in nests or cords, or randomly distributed. The stroma is variably myxoid or collagenous. Eighty percent (80%) of cases show an incomplete rim of lamellar bone or calcification, usually within or just underneath the fibrous pseudocapsule. Immunohistochemistry shows the tumor to be vimentin and S-100 positive. It may also express Leu-7, NSE, and/or GFAP. To date, OFMT does not express cytokeratin.

Electron microscopy characteristically shows abundant intracytoplasmic intermediate filaments, often in perinuclear whorls. There is also reduplication of the external laminae similar to neural tumors.

Chromosomal analysis has shown a loss of chromosome 6, extra material of unknown origin attached to the long arm of chromosome 7, and an unbalanced translocation involving the short arm of chromosome 6 and the long arm of chromosome 14.

Although the line of differentiation of OFMTs has been disputed since its initial description, neural origin is now favored. Supportive of this are its encapsulation, ultrastructural appearance, and the tumors ability to express neural antigens such as S-100, Leu-7, NSE, and GFAP.

The differential diagnosis of OFMT includes epithelioid and spindled neoplasms which variably show a myxomatous component and include:

Epithelioid nerve sheath tumors (NSTs)
Chondroid syringoma
Myxoid chondrosarcoma, and
Epithelioid smooth muscle tumors

Epithelioid NSTs are generally distinguished from OFMT by the following characteristics:

Epithelioid Neurofibroma / Epithelioid Schwannoma / Epithelioid MPNST
- Unencapsulated
- May be plexiform
- Usually hypocellular
- Undulating fibrillary back-
ground / - Abrupt bimorphic histology
(Antoni A & B areas)
- Nuclei elongated,
pointed and wavy
- ‘Nuclear palisading’
- Thick walled vessels / - Highly cellular
- Increased mitoses
- Herringbone pattern
may be present
- Necrosis may be present

Chondroid syringoma (mixed tumor) usually occurs in the dermis or subcutis. Unlike OFMT it contains tubules, and is positive for epithelial markers.

Myxoid Chondrosarcoma usually has abundant intracytoplasmic glycogen (PAS stain) which is lacking in OFMT. Another distinction is the lack of fibrous regions.

Epithelioid smooth muscle tumors show either incomplete myogenous expression (actin positive, desmin negative), or complete myogenous expression (actin positive, desmin positive), findings confirmed by ultrastructure. Unlike OFMT, they do not express S-100.

OFMT usually behaves in a benign fashion with about a 30% local recurrence rate. Occasional tumors, however, are known to have metastasized, usually to lung, and only after multiple recurrences. Unfortunately it is has not been possible to prospectively predict behavior in all tumors, but in an attempt to prognosticate, some authorities are now separating OFMTs into atypical and malignant categories. Proposed criteria suggesting malignancy are increased cellularity, increased mitotic activity, and more centrally-placed regions of osteoid and/or frankly osteosarcomatous regions. Complete surgical excision with clear margins is the suggested initial treatment of choice.

Acknowledgement

Images for Figs. 5a and 5b were taken from the web site of The Society for Ultrastructural Pathology,

CTTR S Case of the Month

May, 2003

Myxomatous regions were microcystic (Fig. 4a) or diffuse (Fig. 4b).

Acknowledgement

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