Plexiform fibrohistiocytic tumor: ultrastructural studies may aid in discrimination from cellular neurothekeoma.

Department of Pathology, The Children's Hospital, Aurora, Colorado 80045, USA.
Ultrastructural Pathology (Impact Factor: 1.13). 12/2009; 33(6):286-92. DOI: 10.3109/01913120903348860
Source: PubMed

ABSTRACT Plexiform fibrohistiocytic tumor is a low-grade soft tissue malignancy that can at times be difficult to differentiate from the less biologically aggressive cellular neurothekeoma. The two entities, which may display identical clinical and histological features, cannot be distinguished by immunohistochemical or molecular diagnostic means. Electron microscopy may enable the accurate identification of problematic examples and thus aid in resolving these occasionally occurring diagnostic dilemmas. To illustrate typical variations in the ultrastructural appearance of plexiform fibrohistiocytic tumor, the authors present two diagnostically noncontroversial examples, and to demonstrate the potential diagnostic utility of electron microscopy in this setting, they present an example of plexiform fibrohistiocytic tumor that could not otherwise have been distinguished from cellular neurothekeoma.

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    ABSTRACT: Background Neurothekeoma represents a neoplasm of uncertain histogenesis that often occurs on the head and neck of younger individuals. Distinguishing neurothekeoma from other tumors, particularly malignancies such as melanoma, can be difficult given the variable presence of nuclear atypia, mitoses and extension into fat or skeletal muscle. KBA.62 represents an anti-melanoma monoclonal antibody that marks approximately 93% of melanomas. This study sought to evaluate KBA.62 expression in neurothekeomas, both as means of affirming the diagnosis and as a potential confounding factor in excluding a melanocytic process. Methods Eighteen neurothekeomas from 17 patients were analyzed by light microscopy and immunohistochemistry. Immunohistochemistry was performed with KBA.62, S100 and CD10 antibodies. The diagnosis of neurothekeoma was confirmed by at least two dermatopathologists. ResultsAll cases showed similar light microscopic and immunohistochemical features. With the exception of two cases, cells expressed CD10 and exhibited morphologic features consistent with neurothekeoma. All 18 cases were S100 immunonegative. The epithelioid cells of all neurothekeomas were KBA.62 immunopositive, including both of two neurothekeomas occurring in the same patient. Conclusions In this study 100% of neurothekeomas tested were KBA.62 positive, admittedly to varying degrees, suggesting the utility of this reagent as being supportive of the diagnosis of neurothekeoma.
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    ABSTRACT: Plexiform fibrohistiocytic tumor is an extremely rare soft tissue tumor with a low malignancy potential. The patient is usually a child or a young adolescent and the tumor is usually localized in the upper extremities. We report on a case of a 21-year old male with a plexiform fibrohistiocytic tumor in the left fibula admitted to our hospital due to a swelling and pain in the left lower extremity. Radiologically a lytic lesion in the distal end of left fibula consistent with a non-aggressive lesion with low biological activity was found. Treated with curettage, the specimen revealed plexiform proliferation of mononuclear histiocyte-like cells, multinucleated osteoclast-like cells, and spindle fibroblast-like cells in variable proportions histopathologically. Immunohistochemical stains were positive for CD68 in scattered fashion in histiocytes and giant cells, and spindle like cells showed positivity for smooth muscle actin. Under electron microscopy, rough endoplasmic reticulum and collagen bundles in the spindle cells suggested fibroblastic differentiation. Also multiple large electron-dense lysosomal granules in histiocytoid cells were found. Multinucleated giant cells exhibited osteoclast-like appearance. All these findings suggested plexiform fibrohistiocytic tumor. Interestingly, the tumor was localized in bone. During the follow up for 27 months after the resection, there was no recurrence or metastasis.
    Pathology International 11/2013; 63(11):554-8. DOI:10.1111/pin.12100 · 1.59 Impact Factor
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    ABSTRACT: Cellular neurothekeoma is a frequent source of diagnostic difficulty. In order to gain more insight into the range of histologic features of cellular neurothekeoma, we examined all cases from our institution, with a focus on describing atypical histologic features. Cases with sufficient histologic material for evaluation were retrieved. Cases were analyzed for demographics, growth pattern, myxoid stroma, cytologic atypia, mitotic rate, perineural invasion, and other histologic features. The 37 patients (16 M; 21 F) had a mean age of 31.0 years (range: 4-89). Tumors involved the head and neck (n=16), arms (n=11), trunk and shoulders (n=8), and foot (n=2). All cases had at least focal nesting of epithelioid to spindled tumors cells characteristic of cellular neurothekeoma. In many, alternate growth patterns were present and represented the dominant pattern in some. These patterns included fascicular (n=9), sheet-like (n=6), and corded (n=4). Myxoid stroma was present in 14 and was prominent in 5. Cytologic atypia was present in 19 patients, with 3 having severe atypia. Mean mitotic rate was 2.0/mm(2) (range 0-10 per mm(2)). Neurotropism was seen in four cases. Other unusual features included collagen trapping, giant cells, hemorrhage, lymphocytic cuffing, chondroid stroma, and cellular vacuolization. Cellular neurothekeoma has a wider range of features than is commonly recognized. The presence of nests of epithelioid tumor cells with characteristic cytologic features, no matter how focal, is a clue to the diagnosis.Modern Pathology advance online publication, 1 November 2013; doi:10.1038/modpathol.2013.190.
    Modern Pathology 11/2013; DOI:10.1038/modpathol.2013.190 · 6.36 Impact Factor