Unilateral renal oncocytosis and combined hybrid tumor: a case report and review of the literature

Emerging entities in renal cell neoplasia: thyroid-like follicular renal cell carcinoma and multifocal oncocytoma-like tumours associated with oncocytosis

The list of accepted entities of renal cell neoplasia has burgeoned since the turn of the century through recognition of rare tumour types and the discovery of genetic mutations driving renal neoplasia syndromes. This growth has not finished and in this report we present examples of each of these types which were not included in the 2016 World Health Organization classification of renal neoplasia, but are candidates for inclusion in the next edition of the classification. Thyroid-like follicular renal cell carcinoma is a rare tumour type with a distinctive microscopic appearance resembling follicles of the thyroid gland. Thirty-nine cases have been described and the findings have been reasonably consistent. Oncocytoma-like tumours associated with oncocytosis arise as a result of somatic mutations in the mitochondrial genome. The differential diagnosis is mainly with the renal lesions of the Birt-Hogg-Dubé syndrome, which is the result of germline mutations in the folliculin gene. Patients with oncocytoma-like tumours associated with oncocytosis are at great risk of developing renal failure as the proliferating lesions replace the renal parenchyma. Oncocytoma-like tumours have never been found to metastasise.

Incidence and histologic features of mixed renal tumors

BACKGROUND AND OBJECTIVES

Guidelines for management of renal cell carcinoma (RCC) incompletely address the implications of mixed renal tumor histology. We investigate the incidence of mixed renal tumors identified at renal surgery and determine the association with pathologic features.

METHODS

Institutional kidney tumor database was reviewed to identify 536 patients who underwent partial or radical nephrectomy. Clinical, demographic, and pathologic data were collected. A linear fixed effects model and logistic regression determined the association of mixed tumor histology with tumor size, stage, grade, and nephrometry score.

RESULTS

Three hundred and eighteen men and 218 women with a median BMI of 31 and median tumor size of 3.5 cm were included. 469 (87.5%) patients had pathologic kidney cancer with the most common histologies being clear cell carcinoma in 343 (73.1%) patients, papillary in 81 (17.3%) patients, and chromophobe in 25 (5.3%) patients. Twenty (4.3%) patients had mixed tumors on final pathology. Clear cell RCC was the most common primary pathology in patients with mixed tumor histology (n = 14, 75%) with additional primary tumor histologies included papillary and chromophobe. When considering secondary histologies, 85% were coexistent primary renal cancers while 15% (n = 3) were benign renal tumors. No association of mixed tumor histology and adverse pathologic features was noted.

CONCLUSIONS

Mixed tumor histology is an uncommon entity that is not associated with adverse features in a solitary renal mass. These results are especially relevant in discussing the role of renal mass biopsy, and provide further evidence that renal sampling is a valuable tool in the appropriate clinical context.

Computed Tomography Appearance of Renal Hybrid Oncocytic/Chromophobe Tumors

OBJECTIVE

A series of renal hybrid oncocytic/chromophobe tumors (HOCTs) was retrospectively assessed for morphologic features and enhancement characteristics by computed tomography (CT).

MATERIALS (SUBJECTS) AND METHODS

Nine patients with pathologically proven HOCTs were identified. These patients harbored a total of 12 lesions. All patients had available preoperative contrast-enhanced CT examinations, although a proportion of the studies had been carried out at outside institutions. The morphologic characteristics and enhancement patterns of each tumor were evaluated systematically.

RESULTS

Seventy-eight percent of the patients were men, with a mean age of 62 years. None of the patients had evidence of metastatic disease at the time of surgery. Mean tumor diameter was 4.4 cm. All the lesions were solid and well circumscribed. Calcifications were not seen in any of these masses. Thirty-three percent of the tumors demonstrated a central stellate hypodensity pattern, whereas a further 42% of the tumors demonstrated a heterogenous appearance. Mean attenuation values were 25.7 HU (noncontrast), 77.4 HU (arterial), 124.8 HU (venous), and 76.8 HU (delayed). Tumor-to-cortex ratios for the 2 enhanced phases (arterial and venous) were 0.56 and 0.79, respectively.

CONCLUSIONS

A series of HOCTs were found on CT to have 2 distinct patterns-a heterogenous enhancement pattern and an "oncocytoma-like" pattern with a central stellate hypodensity. Although the prospective diagnosis of HOCTs on the basis of CT findings is unlikely, an awareness of the existence of these lesions is important as new means of characterizing renal masses on imaging arise.