In pediatric tumors the capsule retracts when the first cut is made and this may obscure the relationship of tumor, pseudocapsule, renal capsule and perirenal tissue. Instead, immersion of the specimen in formalin in the refrigerator for an hour or two can be used to make the outer layers of the specimen firmer and then the specimen should be dissected with parallel slices so that the relationship of the tumor to surrounding tissue can be fully evaluated. Since renal tumors in children often dwarf the small kidneys of these patients, the weight of the specimen often is given as the weight of the tumor. Next make a series of parallel slabs in the sagittal plane at 2-3 cm intervals. Place the entire specimen in a large container of buffered formalin for fixation overnight.
Refrigerated fixation is superior to fixation at room temperature.
Fixation before further sampling may delay the final report, but the results are much better. Before further gross inspection and description are done cut the fixed slices in 1 cm intervals with a long large sharp knife. Take one block from each tumor area that differs in color, especially from areas which are white and grey. Sections from the periphery of the tumor are superior to those of the center because they show the interface with the kidney and other tissues and because necrosis is more common near the center. One generous section of tumor per 2 cm of tumor diameter is probably sufficient.