Synovial metastasis of the knee in a KRAS mutant rectal adenocarcinoma patient

Abstract

Synovial metastasis is an unusual entity in solid tumours and only a few cases have been reported in the literature. We report a case of synovial metastasis of the knee in a young patient with progressive rectal adenocarcinoma and review previously published case reports of synovial involvement in advanced colorectal carcinomas. Synovial metastasis is just one of the multiple possibilities of differential diagnosis in patients with cancer suffering from monarthritis. Radiological tests (plain radiographs, bone scans, MRI of the joint and so forth) can be unspecific and cytological examination of the synovial fluid and/or histology of synovial biopsies is essential for a definitive diagnosis so as to tailor the best treatment for patients. Given the poor prognosis associated with these intra-articular secondaries, treatment is often limited to palliation.

Keywords: chemotherapy; colon cancer; pathology; radiology.

Figure 1

MRI right knee proton density-weighted sagittal image demonstrates a large joint effusion, and diffuse thickening and nodularity of the synovium with homogenous enhancement. No evidence of bony erosion or bone marrow oedema. Enlarged lymph nodes are noted in the superior popliteal fossa.

Figure 2

Macroscopic picture of synovium right knee. An enlarged, unorientated and irregularly shaped portion of glistening gelatinous tissue measuring 180x80 up to 50 mm. Sectioning through the tumour demonstrates a uniform, gelatinous consistency.

Figure 3

Biopsy of the synovium. Picture showing infiltration of the synovial membrane by adenocarcinomatous glands, displaying cribriform growth pattern, typical of colorectal origin (H&E–safran, original magnification ×40). Immunohistochemistry was performed and the malignant cells demonstrated strong nuclear labelling with antibodies for CDX2 and CK20 in keeping with a colorectal primary.