An uncommon neoplasm of the kidney

Clinical History

A 50-year-old woman arrived in our department to undergo a CT examination of the abdomen after an US examination, performed for pain in the right flank, showed a solid formation in the right kidney. The patient did not report haematuria.

Imaging Findings

Plain CT show a solid, well-defined formation measuring approximately 7 x 4.8 x 6 cm (CC x AP x LL) likely arising from the pelvis of the right kidney. In the arterial phase of contrast enhancement the formation shows early and mildly inhomogeneous enhancement. In the venous phase the formation is more hypodense than the renal parenchyma. In the delayed contrast enhancement scans, the formation shows an evident extrinsic compression of the pelvicalyceal system, best visualized in MIPs reconstructions, without CT signs of infiltration. The patient underwent radical nephrectomy.

Discussion

Solitary fibrous tumour (SFT) is an uncommon neoplasm of mesenchymal origin. SFT was first reported in 1931 as a pleuric tumour [1]. SFTs are rare spindle cell neoplasms that usually arise in the pleura; they are considered a variant of haemangiopericytomas [2]. In recent years there have been several reports of SFT arising in other organs like upper respiratory tract, lung, mediastinum, liver and urogenital organs [3]. Renal SFTs are extremely rare. In many cases the origin of SFT of the kidney is difficult to determine as it may arise from the renal capsule, interstitial tissues or peripelvic connective tissues. Around 90% of renal SFTs are benign [4]. Mean age of presentation is 52 years, male-to-female ratio approximately equal to 1. The right kidney is more often affected than the counterpart; in the kidney the renal capsule is the most common site of origin of SFT [4]. Clinical presentation varies between an incidental finding on radiological imaging to a palpable mass. Pain in the right flank and gross haematuria are common symptoms; in rare cases SFT obstructs the pelvi-calyceal system causing hydronephrosis. Radiological studies are the best tools to identify and study the extent of these tumours. US is a reliable diagnostic tool to detect renal SFTs; they present as hypo- or heterogeneous echogenic masses with relatively well-defined margins. CT examinations are more accurate to detect vascular supply and local extent of neoplasm. Plain CT shows a well-circumscribed lobulated lesion; enhanced CT shows a strong enhancement [5], sometimes associated with areas of haemorrhage and necrosis. MRI is rarely performed; due to the presence of collagen the tumour usually shows a low-to-intermediate signal intensity on both T1 and T2-weighted sequences [4, 5]. SFT must be differentiated from other tumours like haemangiopericytoma, angiomyolipoma, leiomyoma, schwannoma, sarcomatoid renal cell carcinoma or neurofibroma; immunohistochemical examinations (diffusely positive reactivity for CD34 and Vimentin) is the main diagnostic method [4, 5].
The majority of renal SFTs exhibits benign behaviour. Although the clinical course of SFTs is rather unpredictable, the prognosis is generally favourable. It is considered that up to 10% of extrathoracic SFTs will recur or metastasize [1, 4, 6]. SFT is considered an intermediately malignant, rarely metastasizing neoplasm. Nowadays laparoscopic radical nephrectomy is the mainstay of therapy of renal SFT. The role of adjuvant chemotherapy is still unclear. All patients need to be on long term follow-up.

Differential Diagnosis List

Final Diagnosis

Solitary fibrous tumour of the kidney

URL:	https://www.eurorad.org/case/12276
DOI:	10.1594/EURORAD/CASE.12276
ISSN:	1563-4086