Renal mass, gross pathology photograph of a resected pediatric kidney with an intraparenchymal neoplasm. Modality: Gross pathology; Coronal/transverse cut surface. The kidney shows a large, soft, pale tan to pink mass replacing most of the renal parenchyma with heterogeneous appearance due to hemorrhagic and necrotic foci. The lesion is friable and poorly circumscribed relative to the surrounding cortex, with indistinct margins and occasional satellite nodules evident on the cut surface. The capsule may be variably thinned or breached at the center. Scale bar indicates 2 cm, illustrating a mass several centimeters in greatest dimension. No visible calcification is apparent in this section. The gross appearance aligns with high-grade renal neoplasms in infancy, most characteristically rhabdoid tumor of the kidney (RTK). RTK typically affects children under 5 years, presents as abdominal mass and/or hematuria, and shows aggressive behavior with early metastatic spread. This image emphasizes the gross phenotype: large, soft, fleshy, hemorrhagic, necrotic intrarenal mass with possible satellite nodules. Clinically, RTK requires prompt genetic workup for SMARCB1/INI1 deficiency and multidisciplinary management. This specimen is valuable for educational discussion of differential diagnoses against Wilms tumor, clear cell sarcoma, and other pediatric renal neoplasms. Useful for pathology curricula and radiologic-pathologic correlation.

Gross pathology image of a renal tissue specimen showing a cross-section through the renal medullary region. The cut surface reveals numerous round to ovoid cystic-appearing spaces embedded within a tan-orange parenchyma, giving a sponge-like architecture consistent with dilated collecting ducts in the renal medulla. The cortex appears relatively preserved with no large focal necrosis or mass effect. The cavities are irregular in size but show a radial distribution toward the papillary tips, suggestive of medullary collecting duct dilation. The overall impression is compatible with medullary sponge kidney (MSK), a congenital malformation of the collecting system. MSK is usually bilateral, slightly more common in males, and frequently clinically silent; symptoms—when present—include nephrolithiasis, hematuria, and recurrent infection, typically in the third to fifth decades. The condition is often sporadic (~95%), with a genetic predisposition suspected in about 5% of cases. Associations include congenital hemihypertrophy, Beckwith-Wiedemann syndrome, Ehlers-Danlos syndrome, Wilms tumor, and multiple endocrine neoplasia type II. Clinically, recognition of this pattern informs differential diagnoses of medullary calcifications and recurrent stones and guides imaging follow-up with CT urography or MRI. This specimen highlights the distinctive medullary sponge morphology relevant for education, radiology correlation, and surgical planning when symptomatic. Clinical history should be considered globally.