Differential diagnosis, investigations and treatment:
Upon this admission, routine lab tests and imaging were performed.
Laboratory examination revealed elevated ESR (100 mm/hour) and increased
serum creatinine (1.6 mg/dl). Non-enhanced chest and abdominopelvic CT
with reconstruction of volumes at 1mm slice thickness showed bilateral
isodense renal pelvis masses without calcification and with a maximum
diameter of 80 x 75 x 92 mm on the right and 90 x 102 x 126 mm on the
left side. Multiple non-significant mediastinal and periaortic lymph
nodes were also detected with a maximum short-axis diameter (SAD) of 8
mm. No skeletal blastic or lytic lesions were noted (Figure 1).
For further evaluation of the renal lesions, abdominal magnetic
resonance imaging (MRI) was carried out by a 1.5 Tesla scanner (Magnetom
Avanto; Siemens Healthineers, Erlangen, Germany) using a sixteen-channel
phased array coil. MRI images included standard sequences such as
T1-weighted, T2-weighted, diffusion-weighted imaging (DWI) with b-value
of 50-400-800 s/mm2 and apparent diffusion coefficient
(ADC) maps. In addition, contrast-enhanced 3-dimensional T1-weighted
gradient-echo was performed in axial and coronal planes. The renal
pelvis lesions displayed hypointense to isointense signals on
T1-weighted images and were isointense to hyperintense on T2-weighted
images with slight heterogeneity. On ADC maps, mild restricted diffusion
with low signal intensity was exhibited. Masses had gradual enhancement
without washout in the delayed phase. Bilateral hydronephrosis along
with signs of parenchymal loss (predominantly in the left kidney) was
also noted but neither perinephric nor subcapsular mass-like lesions
were seen. Other vital organs were preserved without any signs of
infiltration and no abnormal signal or enhancement was found in the
periaortic lymph nodes (Figure 2). To reach a definite diagnosis,
CT-guided core needle biopsy was performed, which showed marked
inflammatory cell infiltration with predominance of lymphocytes, plasma
cells and activated histiocytes without any evidence of granuloma
formation; however, the histopathological findings were inconclusive.
Due to persistently raised creatinine, the patient subsequently became a
candidate for surgery and underwent right partial nephrectomy and left
radical nephrectomy with a small residual mass remaining due to
technical difficulties of complete resection. Histopathologic
examination of surgical specimens revealed diffuse histiocytic
proliferation and plasma cell infiltration, which was in favor of a
histiocytic proliferative disorder, and the subtle presence of
emperipolesis raised the suspicion for RDD. Finally, immunohistochemical
(IHC) assay stained positive for S100 protein and negative for CKAE1/AE3
and CD-1a, confirming the diagnosis of RDD. Approximately 6-7 % of the
plasma cells also stained positive for IgG4.