Case report of a symptomatic giant renal oncocytoma

Abstract

Renal oncocytomas are benign tumours, often asymptomatic, and picked incidentally on radiological imaging. We present a case report of a symptomatic giant renal oncocytoma in a 61-year old man having lower back/right flank pain. A large right renal mass was identified on abdominal CT scan. Radiological features were not sufficient to differentiate this lesion from renal cancer. Right radical nephrectomy was performed. Typical features of oncocytoma, without evidence of malignancy, were seen on histological examination of the specimen. In this report, we discuss literature review of radiological, genetic, and pathological characteristics of renal oncocytoma.

1. Introduction

Renal oncocytomas account for 3–7% of all solid renal masses.¹ Males are affected more commonly and the mean age of presentation is 6–7th decade. Most oncocytomas are single and unilateral, although 4–5% are bilateral and 13% are multifocal. Oncocytomas are usually of small size (average size 4.9 ± 2.7 cm).² Large oncocytomas are rare however, prognosis of giant oncoytomas is not reported differently from the smaller lesions.

2. Case presentation

A 61-year old male was investigated for lower back and right flank pain. He had no systemic and lower urinary tract symptoms. On physical examination, he had a palpable abdominal mass in right upper quadrant. Routine haematological and biochemical tests were normal. Computer tomography (CT) imaging showed a solid enhancing hypodense lesion, replacing the entire right kidney (Fig. 1). The patient had an open right radical nephrectomy via a supra-11th rib right flank incision. A large right renal tumour was identified with no evidence of extra-renal extension. The right kidney was mobilized and radical nephrectomy was performed. Postoperative recovery was uncomplicated.

Fig. 1.

Contrast-enhanced CT image of the abdomen shows enhancing right renal mass of mixed solid and cystic composition.

The specimen weighed 2500 g and measured 25 × 16 × 16 cm (Fig. 2a). Histopathologic evaluation was consistent with a renal oncocytoma without evident renal cell carcinoma. The tumour was confined to the kidney with no lympho-vascular invasion (Fig. 2b).

Fig. 2.

(a) The specimen (post fixation in formalin) shows circumscribed tumour with central area of scarring (red arrow). Residual normal renal parenchyma (black arrow) can also be identified. (b) Microscopic (×100) analysis of H & E stained tumour shows the classic architecture of an oncocytoma; conglomerate islands of cells separated by a pale-staining myxoid stroma (For interpretation of references to colour, the reader is referred to the web version of this article.).

3. Discussion

Oncocytoma is the most common benign solid renal tumour. This tumour represents a distinct pathologic entity first described by Zippel in 1942. In 1976, Klein and Valensi published a case series of patients with oncocytomas and highlighted the benign course of disease and its discrete pathologic features.³ Clear cell renal carcinoma (RCC) may co-exist with oncocytoma in the same or contra lateral kidney.⁴ Usually these lesions are incidental findings in work-up for other reasons, but haematuria is the most common complaint in symptomatic patients.¹

Oncocytomas are commonly associated with three characteristic genetic abnormalities, however in a number of cases, no chromosomal abnormalities have been detected. The genetic associations are: (i) loss of chromosome Y or monosomy 1, (ii) translocations in the 11q13 area and (iii) genetic abnormalities such as trisomy, monosomy and/or a loss of heterozygosity.⁵ These genetic changes are specific for oncocytoma and are not seen in RCC.⁶

On gross appearance, these tumours are cortically localized, light brown or tan, homogenous, well circumscribed with a commonly seen central scar. The central scar represents an avascular area which develops as the tumour grows. Oncocytoma is comprised solely of oncocytes. The origin of these cells is considered to be the intercalary cell of the cortical portion of the collecting tubule. An oncocyte is a round shaped or polygonal cell with moderate to abundant granular cytoplasm, most commonly arranged in a nest. Although oncocytomas are benign, atypical histological features may be present, including cellular atypia or pleomorphism (12–30%), haemorrhage (20–30%), and extension into perinephric fat (11–20%).⁷ Like oncocytoma, the chromophobe subtype of renal cell carcinoma is also derived from the distal tubules and histological similarities exist. However, distinctive cytogenetic and immune-histochemistry suggest individuality of these tumours.

The exact incidence of the giant oncocytomas is not known. In recent era, largely due to wide spread radiological imaging, these tumours are detected early (small and asymptomatic). The largest oncocytoma in the literature measured 27 × 20 × 15 cm and weighed 4652 g.⁸ Banks et al. reported the second largest renal oncocytoma (3090 g, 21 × 18 × 15 cm).⁹ Large renal oncocytomas can be asymptomatic. The largest asymptomatic renal oncocytoma (3353 g, 20 cm) treated at the time of first presentation was reported by Sundararajan et al.¹⁰ This tumour was associated with hypertension which resolved after radical nephrectomy. We present a case of a symptomatic renal oncocytoma. The patient was presented with a dull constant right flank and back pain, likely secondary to pressure effects of the growing tumour. To our knowledge this case is now the second largest reported symptomatic renal oncocytoma (25 × 16 × 16 cm).

Like other renal lesions, renal ultrasound, CT, MRI, and angiogram are helpful for characterisation of oncocytoma. On CT scan the renal oncocytoma are typically hyper-vascular, homogeneietyous, and presents a characteristic central scar. While on MRI T1-weighted imaging, it appears well-defined, homogeneous, isointense to hypo-intense lesion and on T2-weighted imaging, as isointense to slightly hypo-intense with a mildly hyper-intense central scar. A spoke wheel appearance may be observed at angiography. All these radiological findings are of poor predictive value. Although presence of these features are suggestive of oncocytoma yet these are not definitive.¹¹ For smaller renal lesions the role of CT guided biopsy has been studied, however for larger lesions value of the biopsy is limited. Given the uncertainties about preoperative diagnosis, most authors recommend aggressive management with thermal ablation, partial nephrectomy, or radical nephrectomy, depending on the clinical circumstances.¹² These interventions could be regarded as over-treatment, considering the benign nature of the renal oncocytomas. However, often due to lack of definite preoperative diagnosis, these therapeutic approaches are justified. Oncocytomas are benign tumours, and the prognosis after total or partial nephrectomy is excellent. Recurrence at the resection site has not been reported. Few cases of metastases have been reported in the literature,¹³ but these probably represent chromophobe RCC rather than true oncocytomas.

The present case emphasizes the difficulty in differentiation between an oncocytoma and renal cell carcinoma preoperatively. There are no specific presumptive clinical, radiological and laboratory findings that can distinguish oncocytoma from other renal masses. The definite diagnosis depends only on histological examination.

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