Microscopic description:

The tumor consists of sheets of monomorphic oval to plump spindle cells with a prominent perivascular growth pattern. Tumor cells show mild to moderate cytoplasm with indistinct cell borders and irregular infiltration of the renal parenchyma.

The tumor cells stained positive for TLE1, WT-1, CD99(weak) and CAIX (focal) and negative for RCC, CD57, CK7, Desmin, CAM 5.2, AE1/AE3, CD34, CD10, AMACR, HMB45, SOX10, PAX8, S100, SMA.

Based on microscopic description and IHC, the tumor shows features compatible with Primary Renal Synovial Sarcoma.

Discussion:

Primary renal synovial sarcoma is the rarest type of renal sarcoma, comprising <1% of all renal tumors. About 50 cases have been reported in literature thus far.

Affects young people between 20 and 50 years of age, no gender predilection.

On imaging, it is seen as solid or cystic, solid tumors, heterogeneous enhancement, hemorrhage, and necrosis within the tumor, as well as calcification and renal hypovascular tumors.

Usually presents as well defined large masses with morphology varying from irregular outline to smooth cystic lesions.

Histologically, it is classified into biphasic, monophasic, spindle cell and poorly differentiated types. The poorly differentiated variants comprise 20% of cases, have the poorest prognosis and in turn, have three histologic variants: large cell, small cell and high-grade spindle cell variants.

Monophasic type can look like fibrosarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumors, adult Wilm’s tumor, spindle cell carcinoma and spindle cell melanoma. While monophasic synovial sarcoma of the kidney is made up exclusively of monomorphic spindle cells, the biphasic type is a mixture of both spindle-shaped cells and epithelial cells.

IHC: TLE1(nuclear stain)- sensitive and specific for synovial sarcomas, CD56, Bcl2, CD99, EMA (focal) and Vimentin can also be positive. Tumor is negative for CD34, S-100, CD31, Desmin and Actin stains.

Testing for chromosomal translocation t(X;18) (p11.2;q11.2) that causes fusion of SYT gene on chromosome 18 with SSX family gene on chromosome X can help in confirming the diagnosis.

Treatment certainly includes radical surgical resection.

Microscopic image possibly detecting cancerous areas in human tissue
References:

El Chediak A, Mukherji D, Temraz S, Nassif S, Sinno S, Mahfouz R, Shamseddine A. Primary synovial sarcoma of the kidney: a case report of complete pathological response at a Lebanese tertiary care center. BMC Urol. 2018 May 11;18(1):40. doi: 10.1186/s12894-018-0358-z. PMID: 29751751; PMCID: PMC5948733.

Gaurang Modi, Irappa Madabhavi, Harsha Panchal, Asha Anand, Apurva Patel, Sonia Parikh, Swaroop Revannasiddaiah, "Primary Synovial Sarcoma of Kidney: A Rare Differential Diagnosis of Renomegaly", Case Reports in Pathology, vol. 2014, Article ID 657497, 3 pages, 2014. https://doi.org/10.1155/2014/657497

Kawahara T, Sekiguchi Z, Makiyama K, Nakayama T, Nagashima Y, Kita K, Namura K, Itou H, Sano F, Hayashi N, Nakaigawa N, Ogawa T, Uemura H, Yao M, Kubota Y. Primary Synovial Sarcoma of the Kidney. Case Rep Oncol. 2009 Oct 14;2(3):189-193. doi: 10.1159/000245926. PMID: 20737036; PMCID: PMC2914381.

Cai HJ, Cao N, Wang W, Kong FL, Sun XX, Huang B. Primary renal synovial sarcoma: A case report. World J Clin Cases. 2019 Oct 6;7(19):3098-3103. doi: 10.12998/wjcc.v7.i19.3098. PMID: 31624760; PMCID: PMC6795726.

CASE IMAGES