Correspondence Address:
Sinai Khandeparkar Siddhi Gaurish
E-517, The Island, Wakad, Pune - 411 057, Maharashtra
India

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Sir,

Benign nerve sheath tumors of soft tissue can occasionally adopt unusual or unfamiliar morphologic appearance that may introduce difficulties for diagnosis such as multinucleation, bizarre nuclei, intranuclear vacuoles, and other degenerative changes. [1] To the author's knowledge, this is the first case of neurofibroma reported exhibiting both lipomatous differentiation and floret like giant cells (FLGC) and mimicking pleomorphic lipoma cytologically, which has prompted us to report it along with cytohistological correlation and role of immunohistochemical analysis to confirm the diagnosis and prove its benign nature.

A 53-year-old male patient presented with a well-defined, firm, mobile, nontender subcutaneous swelling over lateral aspect of left upper arm since 6 months. The swelling has gradually increased to present size of 1.5 cm × 1 cm. There was no history of trauma and patient had not received intramuscular injection at the site of swelling. Systemic examination findings were unremarkable. Fine-needle aspiration (FNA) was performed, which showed fragments of mature adipocytes admixed with few benign spindle shaped cells and many FLGC with hyperchromatic nuclei. The background was myxoid. A cytological diagnosis of pleomorphic lipoma was offered [Figure 1]. Subsequently, the swelling was excised and sent for histopathological examination. Postoperatively, the patient is disease free with no evidence of recurrence for 9 months.{Figure 1}

On gross examination, the swelling was 2 cm × 2 cm × 1.3 cm, well-defined and glistening tan-white. On cut section white firm areas admixed with yellow soft greasy areas were noted [Figure 2]. On microscopic examination, a well-defined lesion composed of interlacing bundles of elongated spindle shaped cells with wavy darkly stained nuclei and moderate to scanty amount of cytoplasm was seen. Lobules of mature adipocytes were seen embedded in the lesion. At the periphery, nerve fiber bundles were observed. Many FLGC with hyperchromatic nuclei were seen diffusely scattered within the tumor. A diagnosis of neurofibroma with lipomatous differentiation and FLGC was considered [Figure 3]. Benign fibrous histiocytoma was kept as a differential diagnosis (d/d). Representative sections were taken and submitted for immunohistochemical examination. Immunohistochemistry (IHC) was performed with the following panel of antibodies viz. vimentin (clone V9, Dako), S-100 (Dako), CD34 (clone QBEnd10, Novacastra), CD68 (clone 514H12), p53 (clone Do-7, dako) and Ki-67 (clone MM1, Novacastra). The spindle cells showed strong cytoplasmic immunoreactivity for vimentin, and CD34. Both nuclear and cytoplasmic immunoreactivity was seen for S-100. CD68 was nonreactive. The FLGC showed cytoplasmic immnunoreactivity for S-100 whereas CD34, vimentin and CD68 were nonimmunoreactive. p53 was negative and Ki-67 index was <1% [Figure 4]. A diagnosis of neurofibroma with degenerative changes and lipomatous differentiation was made.{Figure 2}{Figure 3}{Figure 4}

Sporadic neurofibroma with FLGC is rarely reported in literature and can pose diagnostic dilemma. [2] Numerous FLGC apparent on low magnification (×100) were identified only in 5.3% of cases in a study of 94 cases which included both sporadic and neurofibromatosis-1 (NF-1) associated neurofibromas. [3] FLGC are occasionally reported in the breast tissue, in the background of pseudoangiomatous stromal hyperplasia in men with NF-1 and gynecomastia. [3] Lipomatous neurofibroma is a new entity, its incidence being 6.9%. [4] Lipomatous differentiation is more commonly seen in schwannoma. [1] To the best of our knowledge, both lipomatous differentiation and FLGC in a neurofibroma has not been mentioned in the literature so far. The etiology of the FLGC is unknown. If it is an incidental finding or is unique to patients with NF is not known. [2],[5] Some regard them as morphological reactive change of the indigenous dermal or endoneurial fibroblasts or dendritic cells in response to unknown micro environmental stimuli. [1] Others think of it as reparative change or a change occurring as a result of hypoxia. [2] Trauma is also thought to be one of the causative factors. [2] Interestingly all the cases are mentioned in males, significance of this finding is although unknown. [2] The lipomatous component in neurofibroma can be focally present with spindle cells or regularly scattered, within the neurofibroma. [4] Such neurofibromas with lipomatous differentiation are found more commonly on head and neck unlike our case. [4] It is regarded as either metaplastic change or aberrant adipose differentiation from mutipotential cells of neural crest origin. [4] Some regard them as senescent change or a result of chronic injury. [6] The d/d of tumors with FLGC is giant cell fibroblastoma, pleomorphic lipoma, multinucleate angiohistiocytoma and giant cell collagenoma. [5] In our case, FNA showed presence of lobules of adipocytes and FLGC with few spindle cells on myxoid background. So diagnosis of pleomorphic lipoma was offered. However d/d of fibrohistiocytic lesion was considered. The hyperchromatic, pleomorphic multinucleated giant cell and the morphological overlap between various components in neurofibroma with both lipomatous differentiation and FLGC can mislead to malignant diagnosis. [5] Cytologically we need to differentiate it from other benign spindle cell tumors and low grade spindle cell sarcomas such as solitary fibrous tumor, low grade fibromyxoid sarcoma, dermatofibrosarcoma protuberance, myxoid synovial sarcoma and low grade malignant peripheral nerve sheath tumor. The absence of cytological features like pleomorphism and mitosis along with IHC studies would help in ruling out malignancy. [5] In our case, spindle cells were immunoreactive for vimentin, CD34 and S-100. FLGC showed immunoreactivity for S-100. CD68 was negative in both spindle cells and FLGC. Thus diagnosis of neurofibroma with lipomatous differentiation with FLGC due to degenerative changes was confirmed. Ki-67 labeling index of <1% and negative p53 confirmed its benign nature. In various studies, the FLGC shows varying patterns of immunoreactivity for S-100, CD34 and CD68. [2] Our experience with present case highlights the rarity of lesion, cytohistological correlation and significance of immunohistochemical analysis in diagnosis. It is hoped that more case studies regarding lipomatous differentiation and etiopathogenesis of FLGC in a neurofibroma, will elucidate the understanding further.

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