The tumor was resected via robot-assisted partial nephrectomy. Histology showed the rare case of a fumarate hydratase deficient renal cell carcinoma.

Fumarate hydratase deficient renal cell carcinoma (FH-RCC) is a very rare tumor, with only a few hundred cases reported in the literature so far. This tumor occurs mostly in young persons in their forties (as opposed to late fifties in papillary RCC). Despite young age and even with a small tumor size, it usually is metastatic at presentation and often has infiltrative characteristics, such as an infiltrative margin, involvement of renal sinus fat, hilar collecting system, and/or renal vein tumor thrombus ^1,2,3.

There are cases due to a somatic mutation and others due to a germline mutation of the FH gene, in which the renal cell carcinoma is part of the autosomal-dominant hereditary leiomyomatosis and RCC (HLRCC) syndrome, as in this case.

On imaging, it is a predominantly cystic (or polycystic) tumor, mostly with thin septa and with an eccentric solid component that has diffusion restriction and peak enhancement in the nephrographic phase ¹.

Typical aspects of this case corresponding with the literature are:

• polycystic appearance and thin septa

• eccentric (T2 hypointense) solid component with diffusion restriction and peak enhancement in the nephrographic phase

Our case is somewhat atypical compared to the majority of cases mentioned in the literature in the following respects:

• there is no infiltrative margin, no involvement of central renal components, and there are no nodal or distant metastases. The tumor is quite small (22 mm maximum diameter)

• our patient had multiple skin leiomyomas, so she apparently had the germline mutation type lesion