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CASE REPORT Table of Contents   
Year : 2008  |  Volume : 51  |  Issue : 2  |  Page : 245-246
Plexiform fibrohistiocytic tumor


1 Ameri Path at Lubbock, TX, USA
2 SWAT Surgical Associates, Lubbock, TX, USA

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   Abstract 

Plexiform fibrohistiocytic tumor is an uncommon mesenchymal tumor that can cause difficulty in diagnosis and surgical management. On clinical and histologic examination, these tumors can potentially be misdiagnosed as sebaceous/epidermal cysts. We report a case of plexiform fibrohistiocytic tumor in a young female, which on initial clinical evaluation was diagnosed as sebaceous cyst. The tumor was deeply invasive, with positive margins on two excisional biopsy specimens. The importance of recognition of this entity, potential pitfalls and prognosis are discussed and the literature is reviewed.

Keywords: Dermatofibrosarcoma protuberans, malignant fibrohistiocytoma, plexiform fibrohistiocytic tumor

How to cite this article:
Thirumala S, Rhyne CD, Bodhireddy S. Plexiform fibrohistiocytic tumor. Indian J Pathol Microbiol 2008;51:245-6

How to cite this URL:
Thirumala S, Rhyne CD, Bodhireddy S. Plexiform fibrohistiocytic tumor. Indian J Pathol Microbiol [serial online] 2008 [cited 2014 Jul 26];51:245-6. Available from: http://www.ijpmonline.org/text.asp?2008/51/2/245/41670



   Introduction Top


Plexiform fibrohistiocytic tumor is an uncommon mesenchymal tumor that can cause difficulty in diagnosis and surgical management. On clinical and histologic examination, these tumors can potentially be misdiagnosed as sebaceous/epidermal cysts. We report a case of plexiform fibrohistiocytic tumor in a young woman, which on initial clinical evaluation was diagnosed as sebaceous cyst. The tumor was deeply invasive, with positive margins on two excisional biopsy specimens. The importance of recognition of this entity, potential pitfalls and prognosis are discussed and the literature is reviewed.

Plexiform fibrohistiocytic tumor (PFX) is a well-documented entity in English language literature. However, these tumors are uncommon and can present many variable features both clinically and histologically, which can pose potential diagnostic pitfalls. Their correct recognition is important to avoid local recurrences and regional and distant/systemic metastases. They have a predilection for upper extremities and young female patients are commonly affected. This tumor was first described in 1988 by Enzinger et al. [1] in a series of 65 cases as a tumor demonstrating morphologic features reminiscent of both a fibrous histiocytoma and fibromatosis. Subsequently, other series [2] and case reports [3] have been described in English language literature.


   Case History Top


A 21-year-old female patient sought medical attention for a slow-growing painless cystic lesion in the trapezius area of her left back. On clinical examination, a firm 2-cm erythematous nodule with cystic areas and a tiny central pore was identified. A working diagnosis of sebaceous cyst was made and the lesion excised.

Our laboratory received unoriented skin with attached subcutaneous tissue, measuring 2.6 cm in maximal dimension. A tiny central pore was also noted on the surface. On sectioning, a firm white nodule extending to the inked deep surgical margin was identified. The entire specimen was routinely processed after formalin fixation and paraffin-embedded.

Microscopically, the lesion was characterized by many pink nodular areas situated predominantly in the deep dermis and widely extending to the underlying subcutaneous adipose tissue [Figure 1]. These nodular areas were composed of round-to-oval cells with no evidence of pleomorphism and mitotic activity. Focal areas demonstrated multinucleated giant cells and hemosiderin-laden macrophages [Figure 2]. These cellular nodular areas were divided by a predominantly pink component consisting of spindle-shaped fibroblastlike cells. A diagnosis of plexiform fibrohistiocytic tumor was rendered and due to positive-margin status in this specimen, the surgeon re-excised the lesion including a segment of trapezius muscle. However, the tumor was deeply invasive and the peripheral margins were again positive for tumor. A wider re-excision was subsequently performed with frozen sections at a later date and the tumor was completely excised.


   Discussion Top


Plexiform fibrohistiocytic tumor is an uncommon mesenchymal tumor first described by Enzinger et al. [1] in 1988 in a series of 65 cases. Subsequently, Ellen et al. , [2] in 1999, published a series of 22 cases. The tumor has a predilection for upper extremity and occurs most frequently in young females. In the first described series by Enzinger et al. , [1],[4] 71% (46 of 65 cases) of the tumors were observed in female patients and the average age at the time of occurrence was 14.6 years. The youngest patient was 2 months old and the oldest patient was 71 years old. Upper extremity was involved in 63.1%, lower extremity in 14%, trunk in 12% and head and neck region in 11% of the cases. Ellen et al. [2] in their series of 22 cases presented a comparatively similar data on age, sex and anatomic distribution for this tumor. The tumor size ranged from 0.3 to 8.0 cm. These tumors most commonly present as solitary painless slow-growing lesions with a central pore, simulating a sebaceous cyst on clinical evaluation. On low-power microscopic examination, they demonstrate a characteristic plexiform arrangement of nodules and fascicles of cells, reminiscent of histologic features of both fibromatosis and benign fibrous histiocytoma. Depending upon the predominant component, this tumor was classified into fibrohistiocytic variant, fibroblastic variant and mixed forms. In Enzinger's series, 43% of the cases demonstrated a predominant fibrohistiocytic component; 17%, a predominant fibroblastic component; and 40% had a mixed component. In Ellen's series, fibrohistiocytic variant was the predominant type (36%), followed by fibroblastic and mixed variants (32% each). Mitotic activity was infrequent (~3/10 hpf) and usually typical, though a higher rate and atypical forms were commonly observed in recurrent tumors.

The differential diagnosis includes various benign and malignant lesions. Benign conditions such as granular cell tumor; plexiform neurofibroma; fibrous hamartoma of infancy; ruptured benign cysts, including sebaceous/epidermal cyst (with which it is often mistaken clinically and occasionally microscopically); fibromatosis; dermatofibrosarcoma protuberans (DFSP); and giant cell tumor are often considered in the differential diagnosis. In the malignant spectrum, fibrosarcoma and malignant fibrous histiocytoma (MFH) enter the differential diagnosis. Careful histologic examination, coupled with clinical correlation and immunostains, helps differentiate this tumor from other diagnostic entities. Caution should be entertained in identifying this tumor and differentiating it from a ruptured cyst with macrophages. The current case was originally considered a ruptured cyst on low-power examination. However, on further careful evaluation, the characteristic plexiform pattern of the tumor with multinucleated giant cells enabled us in arriving at the correct diagnosis.

Plexiform fibrohistiocytic tumor is an intermediate-grade or low-grade malignant neoplasm, which may recur locally if not completely excised. In their series, Enzinger et al. [1] reported a local recurrence rate of 37.5% (12 cases out of 65) and Ellen et al. [2] reported an incidence of 12.5% in their series. Of the 12 cases of local recurrence in Enzinger's series, 2 (16%) cases subsequently developed regional lymph node metastases with a mean interval of 22 months. No pulmonary or other systemic organ metastases were identified in any of the 65 cases described by Enzinger et al. [1] In the series by Ellen et al. , [2] 3 (19%) patients had pulmonary metastases. One (6%) patient aged 4 years at the time of diagnosis died of his extensive metastatic pulmonary disease and fibrosis. [3]

In conclusion, we may state that the present case of plexiform fibrohistiocytic tumor was on clinical and initial morphologic evaluation interpreted as a sebaceous cyst/epidermal cyst with rupture and secondary inflammation. This is a potential pitfall as plexiform fibrohistiocytic tumor is a low-grade malignant neoplasm with a significantly high risk for local recurrence if not excised completely. Though not common, it can metastasize to regional lymph nodes and occasionally, systemic metastases can occur. [3] The correct recognition of this entity and differentiating it from other mimics are crucial to proper patient management and appropriate follow-up.

 
   References Top

1.Enzinger FM, Zhang RY. Plexiform fibrohistiocytic tumor presenting in children and young adults: An analysis of 65 cases. Am J Surg Pathol 1988;12:818-26.  Back to cited text no. 1  [PUBMED]  
2.Ellen RD, Arndt AT, Nascimento AG. Plexiform fibrohistiocytic tumor: Clinicopathologic analysis of 22 cases. Am J Surg Pathol 1999;23:662-70.  Back to cited text no. 2    
3.Solomao DR, Nascimento AG. Plexiform fibrohistiocytic tumor with systemic metastases: A case report. Am J Surg Pathol 1997;21:460-76.  Back to cited text no. 3    
4.Weiss SW, Goldblum JR. Plexiform fibrohistiocytic tumor. In : Enzinger and Weiss's soft tissue tumors. 4 th ed. Mosby Inc; 2001. p. 522-7.  Back to cited text no. 4    

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Correspondence Address:
Seshadri Thirumala
1912 Aberdeen Ave, Lubbock TX 79427
USA
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DOI: 10.4103/0377-4929.41670

PMID: 18603695

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    Figures

  [Figure 1], [Figure 2]

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