The most important differential diagnosis of a renal and perirenal mass is malignancy. However, certain immunological diseases may also present with isolated involvement of the kidney and the perinephric space. We present a case of retroperitoneal fibrosis (RPF) with isolated perinephric involvement, without involving the aorta.
A 67-year-old male, smoker for the past 40 years, without other co-morbidities, was found to have a left renal mass on the sonographic evaluation of the abdomen, obtained for dyspepsia. The contrast-enhanced computed tomography (CECT) scan showed an irregularly shaped hyperdense enhancing mass encasing the left kidney and the left renal vessels, with a 5.7 cm × 5.2 cm sized complex cyst in the lower pole [Figure 1a and b]. Aorta and its major branches, except the left renal artery, were uninvolved. Few lymph nodes in the retroperitoneal and inguinal region were also enlarged. Based on the CECT scan, the possible diagnoses were Erdheim–-Chester disease, hairy cell leukemia or papillary renal neoplasm with secondary hemorrhage. In view of the doubtful diagnosis, a magnetic resonance imaging of the abdomen was performed which showed an irregular mass with altered signal intensity measuring ~10 cm × 11 cm in the left perinephric region. It was hypointense on T1 and T2 and showed restricted diffusion on the diffusion weighted imaging (DWI) [Figure 1c]. On the dynamic postcontrast sequences, the mass showed gradual heterogeneous enhancement, predominantly in the peripheral aspect, with patchy enhancement in the central aspect. The renal hilum, renal artery, and renal vein were completely encased, without any compression or luminal invasion. A possibility of lymphoproliferative or sarcomatoid pathology was suggested. On the diuretic renogram, the differential renal function of the left kidney was 13%. Considering a strong possibility of malignancy and to rule out distant metastasis or primary, a fluorodeoxyglucose-positron emission tomography (FDG-PET) scan was obtained which revealed an irregular heterogeneously FDG avid soft tissue mass (standardized uptake value maximum [SUVmax] 8.8) in the left renal fossa [Figure 1d]. A core-needle biopsy of the mass revealed areas of dense fibrosis with focal storiform pattern with interspersed IgG4-positive plasma cells and histiocytes, suspicious for IgG4-related disease. His serum IgG4 level was 2.06 g/L (normal – 0.86–1.35 g/L).
No investigation could conclusively rule out the presence of malignancy and in addition, the kidney was poorly functioning. Hence, a laparoscopic radical nephrectomy was performed. Intraoperatively, there was a large renal mass with dense adhesions between the Gerota’s fascia and the overlying bowel mesentery. The planes between the lateral border of the aorta and the mass showed dense fibrotic reaction. The postoperative course was uneventful. On gross examination, the cut section showed a homogeneous gray-white lesion with irregular infiltrative borders involving the perirenal fat at the hilar, lower and the upper pole regions of the kidney [Figure 2a]. There was a thick-walled cyst with fine internal septa at the lower pole. On the microscopic examination, an infiltrative lesion composed of large areas of bland-appearing storiform fibrosis intermixed with abundant reactive lymphoid follicles, comprising of large numbers of plasma cells, was found [Figure 2b]. A few veins showed evidence of obliterative phlebitis. On immunohistochemistry with CD38, extensive plasma cell proliferation with few areas showing higher number of IgG4-positive plasma cells (more than 30 IgG4-positive plasma cells per HPF in few foci) was noted, suggesting either idiopathic RPF or IgG4-related disease [Figure 2c]. Since IgG4 levels were not raised significantly, and there was no evidence of tubulointerstitial nephritis in the renal parenchyma, IgG4 disease was ruled out and the diagnosis of RPF was confirmed. The patient is currently doing well at 9-months of follow-up.
Renal parenchyma and the perinephric space may harbor solitary, rind-like, or multiple soft tissue masses, which could be neoplastic or non-neoplastic. The differential diagnoses of circumferential soft tissue masses in the perinephric area, with or without renal parenchymal involvement, include lymphoma, Erdheim–Chester disease, IgG4 disease, and RPF. In our case, the biopsy revealed dense fibrosis with infiltration of the plasma cells and histiocytes. This narrowed down the differential diagnosis to IgG4 disease and RPF. Since serum IgG4 levels were normal, there was a strong suspicion of RPF.
There is an 11%–15% risk of malignancy in the patients with RPF. In a subset of patients, the RPF can be a part of paraneoplastic syndrome of a distant primary malignancy. Patients with renal involvement have been found to have the highest risk of malignancy, especially if the time duration between the diagnosis of RPF and diagnosis of malignancy is <1 year. Since one-tenth of the patients with RPF have renal involvement, it is imperative to rule out malignancy in these cases. The features differentiating RPF from malignancy have not yet been defined. Wang et al. gave a risk stratification model to differentiate RPF from renal cell carcinoma. The three risk factors were the presence of lesion above the renal arteries, SUVmax >6.23 on FDG-PET and retroperitoneal, inguinal, axillary, or supraclavicular lymphadenopathy. The presence of 0–1 risk factors was regarded as low risk for malignancy, 2 risk factors as moderate risk, and 3 risk factors as high risk.
In the index case, SUVmax of the lesion was 8.8 on FDG-PET and there was retroperitoneal and inguinal lymphadenopathy. Thus, as per the Wang risk stratification model, the patient was at moderate risk of having a malignancy. Moreover, the kidney was poorly functioning, so we proceeded with left radical nephrectomy and the final diagnosis could be reached only after the histopathological analysis of the specimen.
RPF is chiefly considered as a manifestation of either isolated autoimmune periaortitis or multifocal fibrosclerosis. It mostly involves the infrarenal aorta and the surrounding structures. Renal and perirenal involvement in RPF has been reported to be almost always associated with periaortitis. In the current case, there was unilateral perinephric fibrosis without periaortitis, which is atypical. To the best of our knowledge, only one such case has been reported till now.
The rare presentations of systemic disease such as RPF must be considered while dealing with the urinary tract. Decisions regarding their management should be taken after considering the risk of cancer, especially in cases where malignancy cannot be confidently ruled out.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship: Nil.
Conflicts of interest: There are no conflicts of interest.
1. Surabhi VR, Menias C, Prasad SR, Patel AH, Nagar A, Dalrymple NC. Neoplastic and non-neoplastic proliferative disorders of the perirenal space:Cross-sectional imaging findings. Radiographics 2008;28:1005-17
2. Lee SJ, Eun JS, Kim MJ, Song YW, Kang YM. Association of retroperitoneal fibrosis with malignancy and its outcomes. Arthritis Res Ther 2021;23:249
3. Mizushima I, Kawano M. Renal involvement in retroperitoneal fibrosis:Prevalence, impact and management challenges. Int J Nephrol Renovasc Dis 2021;14:279-89
4. Wang Y, Guan Z, Gao D, Luo G, Li K, Zhao Y, et al. The value of (18) F-FDG PET/CT in the distinction between retroperitoneal fibrosis and its malignant mimics. Semin Arthritis Rheum 2018;47:593-600
5. Lang JT, Kang N, Zhang JH, Xing NZ. Unilateral perirenal fibrosis without aorta involvement. Eur Rev Med Pharmacol Sci 2015;19:732-5