Journal of Cancer Research and Therapeutics Medknow Publications on behalf of the Association of Radiation Oncologists of India (AROI) ISSN: 0973-1482 EISSN: 1998-4138 Vol. 6, Num. 3, 2010, pp. 388-390

Journal of Cancer Research and Therapeutics, Vol. 6, No. 3, July-September, 2010, pp. 388-390

Case Report

Neurofibroma of kidney: An uncommon neoplasm and diagnostic dilemma with solitary fibrous tumor

Santosh Kumar Mondal, Mamata Guha Mallick, Ranjana Bandyopadhyay, Palash Kumar Mondal

Department of Pathology, Medical College, Kolkata, West Bengal, India

Correspondence Address:Santosh Kumar Mondal, " Tenancy Complex", Flat 1B, Block B, 204 RN Guha Road, Dumdum, Kolkata-78, West Bengal, India, dr_santoshkumar@hotmail.com

Code Number: cr10097

PMID: 21119287

DOI: 10.4103/0973-1482.73347

Abstract

Keywords: Immunohistochemistry, kidney tumor, neurofibroma, spindle cells

Introduction

Neurofibroma is a common benign tumor and two types are identified based on histological and biological characteristics. The most common form occurs in the skin (cutaneous neurofibroma) or in peripheral nerve (solitary neurofibroma). The less common type is the plexiform neurofibroma, which usually occurs in patients with neurofibromatosis type 1.

Solitary neurofibroma originates from peripheral nerve and composed of haphazardly arranged fibroblasts, perineurial cells and Schwann cells. Most commonly, the tumor presents as either a small dermal nodule or a broad-based polypoid skin lesion. Sometimes, it may occur in deeper sites such as subcutis, retroperitoneum and mediastinum. Other rare sites of this tumor are heart, lung, gastrointestinal tract, brain, urinary bladder and kidney.

Case Report

A 54-year-old woman complained of pain in her right lower back and hematuria of five months duration. The clinical examination suspected a right renal tumor. Routine hematological and biochemical investigations were within normal limits. Ultrasonography detected a solid mass in the upper pole of right kidney. Computed tomography demonstrated a well-circumscribed solid tumor and measured approximately 4 cm in diameter. The tumor involved the renal cortex [Figure - 1]. Thrombosis was absent in renal vein or in inferior vena cava. No enlarged lymph nodes were seen in the abdomen. The patient underwent radical nephrectomy for suspicision of renal cell carcinoma.

Pathological findings: A specimen of right radical nephrectomy was received. Cut section revealed a well-circumscribed, unencapsulated firm mass under the renal capsule in the upper pole of right kidney, which involved the cortex. The tumor measured 4 × 3.6 cm. and was glistening, white homogenous; devoid of any cystic and necrotic changes [Figure - 2]. Grossly suprarenal gland, renal vessels, ureter and abdominal lymph nodes were unremarkable.

Microscopically, the tumor consisted of slender spindle shaped cells, fibroblasts accompanied by hyalinized collagenous tissue [Figure - 3]. Mast cells were also present in the stroma. The tumor cells lacked cytologic atypia and showed no mitosis. Suprarenal gland, renal vessels, urethra and abdominal lymph nodes were free of tumor involvement. Based on morphology, differential diagnoses of neurofibroma and solitary fibrous tumor (SFT) were made and immunohistochemistry was suggested. The tumor cells expressed S-100 protein [Figure - 4]. But the tumor cells were negative for CD34 and CD99. Thus, a final diagnosis of neurofibroma was reached.

Discussion

Mesenchymal tumors are relatively uncommon in kidney. Benign mesenchymal tumors that may arise in kidney are lipoma, myxoma, SFT and benign peripheral nerve tumors. ^[1] The first reported case of neurofibroma of kidney was by Neuberg HJ in 1957. ^[2] Over the years, other authors also reported few cases of this entity. ^{[3],[4],[5],[6]}

The majority of neurofibromas are solitary, localized lesion, which present as polypoid or nodular skin lesion. ^[7] Rarely, solitary neurofibroma may occur in deep soft tissue, commonly in an axial location. Grossly, neurofobroma may vary significantly from lesion to lesion. Usually, localized neurofibroma is a circumscribed but unencapsulated lesion, the margins of which are not clearly defined. Microscopically, it has a varied appearance but, in most cases, consists of elongated spindle cells with poorly defined, pale eosinophilic cytoplasm and tapering, wavy or buckled nuclei in a fibrotic background. The stroma contains a rich network of collagen fibers (type I, III, IV, V and VI). Numerous mast cells may be seen in the stroma. ^[8]

Ideally renal masses of 4 cm or small especially originating in the poles of the kidney and amenable to partial nephrectomy are preferred to be treated with nephron sparing approach. It avoids unnecessary nephrectomy. But in our case, clinically and radiologically the tumor was suspected of renal cell carcinoma. So, the surgeon performed radical nephrectomy rather than nephron sparing approach for small (<4 cm) benign tumor. In this case, the tumor was unencapsulated, well circumscribed lesion and composed of benign spindle shaped cells, fibroblasts in a fibocollagenous background. Mast cells were present in the stroma; hence the possibility of neurofibroma was favored over SFT on morphological grounds. However, there is significant overlap in morphological features between neurofibroma and SFT as far as kidney tumor is concerned. Electron microscopic/ Ultrastructural studies are not helpful in distinguishing these two tumors in many cases. Instead, immunohistochemistry is key to the diagnosis. Neurofibroma is reactive for S-100 protein, whereas SFT is strongly reactive for CD34 and currently regarded as clue to diagnosis. SFT, express CD99 and bcl-2 in 70% of cases, smooth muscle actin (SMA) and epithelial membrane antigen (EMA) in 20-35% of cases. ^[9]

In our case, the tumor expressed S-100 protein but non reactive to CD34 and CD99. Hence, a confirmed diagnosis of neurofibroma was established.

To conclude, although morphology is most important in formulating the initial differential diagnosis, the addition of immunohistochemistry is vital in arriving at the correct classification of renal spindle cell tumor. ^[10]

References

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