Myxoid Pseudotumor Involving the Renal Sinus

Abstract

We describe 33 cases of myxoid pseudotumor involving the renal sinus from 31 patients. Patients included 21 men and 10 women, ages 30 to 95 years. Twenty-seven cases (82%) had an associated malignancy, including urothelial carcinoma of the renal pelvis (22 cases), clear cell renal cell carcinoma (3 cases), urothelial carcinoma of the bladder (1 case), and poorly differentiated carcinoma of uncertain lineage (1 case). The remaining 6 (18%) had no associated malignancy and included 3 nephrectomies for ureteral stricture, 2 ureteropelvic junction repairs, and 1 resection of a “periureteral mass” (subsequently shown to be myxoid pseudotumor). Myxoid pseudotumor was identified by preoperative computed tomography imaging in 2 patients (6%) and identified by the gross dissector in 9 cases (27%). The mean size was 14 mm (range: 5 to 38 mm). All cases had an admixture of adipocytes, myxoid stromal matrix, variable collagenization, and a hypocellular population of bland spindled and stellate stromal cells. No multilobated atypical stromal cells were present. Clinical follow-up was available for 28 patients (90%), ranging from 1 to 132 months (mean: 24.6 mo). No patients had adverse events related to the myxoid pseudotumor. Myxoid pseudotumor of the renal sinus is often associated with a variety of adjacent neoplastic and non-neoplastic conditions and may present as a mass lesion detectable by imaging and/or gross inspection. Awareness of this benign process is important to avoid confusion with a neoplasm, especially liposarcoma.

Myxoid Pseudotumor Changes Affecting the Distal Ureter Associated With Urothelial Carcinoma In Situ

“…Myxoid pseudotumor involving the renal sinus has been recently reported by Hogan et al as a benign lesion localized in the fat tissue of the renal sinus and composed of a prominent myxoid matrix, intermingled with the adipocytes, that contains a hypocellular population of non-atypical spindled and stellate cells. 1 This kind of pseudoneoplastic reactive changes are closely related to those previously described in the peritumoral and renal sinus adipose tissue by Tanas et al and Dashti et al 2,3 We would like to report similar pathologic changes affecting not the proximal urothelial tract or the renal sinus region but the distal ureter, in a specimen that showed a diffuse urothelial carcinoma in situ associated.…”

“…Myxoid pseudotumor has proved to be a challenge as it can radiologically mimic a neoplastic process of the kidney or renal pelvis. [1][2][3] In our patient, the CT characteristics in the distal ureter have been similar to those typically found in ureteral neoplasms and the differential diagnosis would be really difficult. Additionally, the final clinical interpretation was complicated by the voided and selective urine cytologies as well as the ureteral biopsy that were diagnosed as high grade urothelial carcinoma.…”

“…As a result, they suggested that maybe myxoid pseudotumor could be related to "irritation" by the effect of a mass, like the tumors, or by the chronic inflammation seen in the non-neoplastic patients. 1,3 Our specimen has been characterized by the absence of an obstructive mass and the inflammatory infiltrate was only mild. It was remarkable, however, that there was an extensive urothelial carcinoma in situ in the ureter.…”

“…1,3 According to the two series of Dashti et al and Hogan et al, diagnostic criteria for this entity are the combination of mature fat, myxoid stromal matrix, variable collagenization and a hypocellular population of bland spindled and stellate stromal cells. 1,3 The three published series make a total of 56 lesions, all of them being located around the proximal urinary tract: 23 were perinephric masses and the 33 reported by Hogan et al specifically involved the renal sinus. [1][2][3] Our lesion, on the other hand, affected the last 3 cm of the distal ureter, and presents the possibility that myxoid pseudotumor can arise in other sections of the urinary tract beside the proximal portion, something which has not been previously reported.…”

“…These emphasized the similarities to a well-differentiated liposarcoma 2 and the myxoid character of the lesion. 1,3 According to the two series of Dashti et al and Hogan et al, diagnostic criteria for this entity are the combination of mature fat, myxoid stromal matrix, variable collagenization and a hypocellular population of bland spindled and stellate stromal cells. 1,3 The three published series make a total of 56 lesions, all of them being located around the proximal urinary tract: 23 were perinephric masses and the 33 reported by Hogan et al specifically involved the renal sinus.…”