A 24-year-old woman presented with a 1.0-cm painless, slowly growing nodule on the right neck (over the clavicle) that had been present for 4 months. Examination revealed a firm subcutaneous nodule that initially was locally excised with a clinical diagnosis of "epidermal cyst." The microscopic examination showed that the lesion was not completely excised. Two weeks later, a wider excision was performed, which indicated that all resection margins were free of tumor. There was no recurrence or metastasis after 6-year follow-up.
The first primary surgical specimen consisted of an ellipse of gray-tan skin measuring 2.6 × 1.0 cm with a 1.2cm-thick layer of underlying yellow fatty tissue. sectioning of the specimen showed a 0.4-cm ill-defined gray-red area, which was on the upper lateral margin. Under the microscope, the lesion measured 5 mm in diameter and was located in the deep dermis-involved junction between dermis and subcutis and extended into the subcutaneous fat tissue (Figure 1). The lesion was composed of mononuclear cells and plump spindle cells arranged in a plexiform pattern. The centrally located mononuclear cells, with a myxoid background surrounded by spindle-shaped cells, formed an individual small cluster. Dense collagenous bands separated the short spindle cell fascicles (Figure 2). The mononuclear cells had ovoid, vesicular nuclei with inconspicuous small nucleolus(i) (1-3) and irregular nuclear contours. The cytoplasm was eosinophilic and moderately abundant. Osteoclast-like multinucleated giant cells were not identified after thorough examination of multiple sections. Immunohistochemistry demonstrated biphasic neoplastic cells characterized by CD68 cytoplasmic positivity in mononuclear cells (Figure 3) and CD34 cytoplasmic positivity in spindle cells (Figure 4). Both cell types were strongly positive for vimentin and negative for muscle-specific actin, S100, pankeratin, and CD45.
What is your diagnosis?
Pathologie Diagnosis: Myxoid Plexiform Fibrohistiocytic Tumor Without Multinucleated Giant Cells
Plexiform fibrohistiocytic tumor (PFT) is a rare lowgrade superficial soft tissue neoplasm of children and adults younger than 30 years of age. Females are affected approximately 3 to 4 times as often as males. The tumor typically presents as a painless dermal or subcutaneous mass, which slowly grows for a period of months or years. The most common location is the upper extremities, followed by the lower extremities, trunk, head, and neck. These tumors can recur and occasionally metastasize to regional lymph nodes and even, rarely, to the lungs. Therefore, this entity is currently categorized as an intermediated malignant fibrohistiocytic tumor. Wide excision and follow-up without radiotherapy are essential components of management for PFT.1"3
Macroscopically, PFT is a relatively small, ill-defined nodule or mass with a gray-white trabecular appearance, located in dermal or subcutaneous adipose tissue and ranging in size from 0.5 to 80 .0 0 cm.3 Microscopically, PFT is composed of small clusters containing biphasic differentiation of fibroblast-like spindle cells and mononuclear histiocytic cells arranged in a characteristic plexiform pattern. The clusters consist of nests of mononuclear histiocytic cells that are often admixed with osteoclast-like multinucleated giant cells, showing no nuclear atypia, necrosis, or significant mitotic activities. The clusters of mononuclear histiocytic cells are circumscribed by short fascicles of fibroblast-like cells that intersperse between collagen bundles. Based on proportion of fibroblast-like spindle cells and mononuclear histiocytic cells, 3 histologie subtypes are established: fibrohistiocytic, fibroblastic, and mixed.1 The fibrohistiocytic type consists of nests of histiocytic cells interspersed with multinucleated giant cells. The fibroblastic type consists of spindle fibroblast-like cells arranged in a plexiform pattern resembling fibromatosis. The histologie patterns and morphologic features, including mitosis, cell atypia, and tumor size, are not related to the prognosis.1'3
The scattered osteoclast-like multinucleated giant cells and mononuclear histiocytic cells were considered to be hallmarks of PFT. As of 2002, two PFTs without multinucleated giant cells had been reported.4,5 All of these 3 cases, including the present one, did not show local recurrence or metastasis after 1-year to 6-year follow-up. It is believed that osteoclast-like multinucleated giant cells are formed by fusion of mononuclear histiocytic cells under effects of certain cytokines and growth factors. Reviewing all available histological images and text descriptions in the literature demonstrated that all recurrent and metastatic PFTs had a multinucleated giant cell component. ^3-6"8 It is likely that PFTs without multinucleated giant cells present as an early stage of PFT development.
The present case is also remarkable for its rarely reported myxoid changes. Only one myxoid PFT was reported recently in a 58-year-old man.9 The authors suggested that myxoid changes may reflect a distinctive behavior of PFTs in older people. On the other hand, myxoid changes in our case in a young woman may represent a kind of degeneration, likely related to the longstanding process commonly seen in PFTs.
Immunohistochemical studies generally indicate that the mononuclear histiocytic cells and osteoclast-like multinucleated giant cells are positive for CD68 and negative for CD45, whereas the spindle fibroblast-like cells are commonly positive for smooth muscle actin and are occasionally positive for CD34.'1 The results tend to favor the notion that these cells are likely derived from (myo)fibroblastic origin. Both mononuclear histiocytic cells, including osteoclast-like multinucleated giant cells and spindle fibroblastlike cells, are positive for vimentin and negative for S100 and epithelial markers.
The differential diagnosis of PFT is rather broad, and the diagnosis includes especially those tumors with a prominent plexiform pattern, such as plexiform neurofibroma, plexiform schwannoma, fibrous hamartoma of infancy, cellular neurothekeoma, fibromatosis, and nodular fasciitis.1,5 Recognition of the characteristic histologie features and application of appropriate immunohistologic panels usually lead to a correct diagnosis.
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3. Remstein ED, Arndt CAS, Nascimento AG. Plexiform tibrohistiocytic tumor: clinicopathologic analysis of 22 cases. Am j Surg Pathol. 1999:23:662-670.
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5. Salamanca J, Rodriguez-Peralto JL, Carcia de Ia Torre |P, Lopez-Rio F. Plexiform fibrohistiocytic tumor without multinucleated giant cells. Am J Dermatopathol. 2002;24:399-401.
6. Segura LG, Harris J, Wang B, Reinzo A, Urken ML, Brandwein M. Plexiform tibrohistiocytic tumor: a rare low-grade malignancy of children and young adults. Arch Otolaryngol Head Neck Surg. 2002:128:966-970.
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8. Salomao DR, Nascimento AG. Plexiform fibrohistiocytic tumor with systemic metastases. Am I Surg Pathol. 1997;21:469-476.
9. Cho S, Chang SE, Choi JH, Sung KJ, Moon KC, Koh JK. Myxoid plexiform fibrohistiocytic tumor. J Eur Acad Dermatol Venereol. 2002; 16:519-521.
Lugen Chen, MD, PhD; Jen H. Lin, MD
Accepted for publication March 11, 2004.
From the Department of Pathology and Laboratory Medicine, Nassau University Medical Center, East Meadow, NY (Drs Chen and Lin); and the School of Medicine, State University of New York at Stony Brook, East Meadow, NY (Dr Lin).
The authors have no relevant financial interest in the products or companies described in this article.
Reprints: Jen H. Lin, MD, Department of Pathology and Laboratory Medicine, Nassau University Medical Center, 2201 Hempstead Turnpike, East Meadow, NY 11554 (e-mail: firstname.lastname@example.org).
Copyright College of American Pathologists Aug 2004
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