Hilar pararenal mass

Clinical History

A 51-year-old woman came to our hospital with complaints of persistent left back pain. The clinical findings and the laboratory tests were unremarkable.

Imaging Findings

An abdominal CT showed an oval para-renal expanding lesion, with a relatively well-defined margin, but without distinct border with the medial aspect of the left kidney. It measured 6x5x4 cm. Spontaneously it had higher density CT values than renal parenchyma and after iodine contrast administration it had slight enhancement (15HU), less than neighbouring renal cortex. Permeability of renal artery was assured and the renal vein was free of thrombus. MR imaging confirmed the oval para-renal hilar mass, adjacent to the medial contour of the left kidney. The mass showed low signal in T1 weighted images (WI) and very low signal in T2 WI. Fat suppression did not change signal intensity of the lesion. There was no evidence of extension into renal parenchyma or of perinephric fat infiltration. The mass lied in front of the psoas muscle with which it had a smooth interface. No enlarged retro-peritoneal lymph nodes were seen.

Discussion

The MR findings confirmed a solid para-renal mass with no detectable macroscopic fat making it a surgical renal mass. The relative high density on unenhanced CT in combination with very low T2 signal intensity gave signs of hemorrhagic nature. The pattern of enhancement, the absence of perinephric fat infiltration and of lymphadenopathy, without invasion into adjacent organs or extension into the renal vein suggested a non aggressive behaviour. However, malignancy could not be excluded. Although renal cell cancers usually grow as focal cortex-based neoplasms [1], they can have an exophytic appearance [2] and can present as hypo-vascular well-demarcated lesions [1], as in this case.
The central location of the mass raised the suspicion of transitional cell carcinoma but the absence of encasement or obliteration of collector system and the absence of distortion of renal sinus architecture or invasion of sinus fat made it unlikely [2].
A renal-sparing surgery was performed and the pathology revealed a PEComa.
PEComa is defined by the WHO as a mesenchymal tumour composed histologically and immunohistochemically of distinctive perivascular epithelioid cells [3, 6]. This family of neoplasms with epithelioid differentiation includes some forms of angiomyolipomas of the kidney and liver, lung lymphangioleiomiomatosis, clear cell “sugar” tumour of the lung and rare clear cell tumours of other organs (pancreas, rectum, abdominal serosal layer, uterus,..). If the major component is epithelioid cells they are classified as PEComa, which has a typical perivascular location. The epithelioid cell has morphologic and immunohistochemical distinctive features such as an epithelioid appearance and imunoreactivity with melanocytic HMB 45 marker, suggestive of perycitic origin [4]. Absence of reactivity to cytokeratin and imunoreactivity with melanocytic and myoid markers usually establishes the diagnosis, as in this case. The cells have mild or no atypia and normal counterpart is not known [3,7].
Surgery is the mainstay of treatment for PEComa at presentation. Primary excision is usually curative but in rare cases of local recurrence or metastasis resection with or without adjuvant therapies may be considered. Given the uncertainty of PEComa tumour biology, although usually benign long term follow up is needed [6, 7].
The clue to the diagnosis was the topography- perivascular in the renal hilum, the low aggressive appearing features with no signs of local invasion and radiologic features of hemorrhagic nature. Although very rare, the radiologist should be aware of them.

Differential Diagnosis List

Final Diagnosis

Perivascular Epiltelioide Neoplasia- PEComa

URL:	https://www.eurorad.org/case/9636
DOI:	10.1594/EURORAD/CASE.9636
ISSN:	1563-4086