Cytologic and Histologic Findings of Nephroblastoma in a Captive Desert Tortoise (Gopherus agassizii)
A 97-yr-old, male, captive desert tortoise (Gopherus agassizii) had a 2-month history of lethargy. Imaging with ultrasound, radiographs, and computed tomography revealed a 10-cm-diameter mass in the caudal coelom. Fine-needle aspiration revealed spindle and epithelial cell proliferations with formation of rosettes. Exploratory surgery was performed and the mass was removed and submitted for pathology. There was no evidence of metastasis on imaging or at surgery. Histology revealed a mass arising from and compressing the kidney. The mass was composed of primitive glomeruli, tubules, blastemal cells, and mesenchymal cells, features that are diagnostic for nephroblastoma. Tubules were reactive to cytokeratin and mesenchymal cells were reactive to desmin via immunohistochemistry; other immunohistochemical markers were either negative (e.g., S-100) or noncontributory (e.g., epithelial membrane antigen, myogenin, vimentin, and Wilms' Tumor 1). This is the first report of nephroblastoma in a chelonian.Abstract
(A) This right lateral radiographic image shows an ovoid, soft tissue opacity mass (asterisk) in the caudal coelom associated with dorsal displacement of the intestines (arrows). (B) Ultrasonographic image from the right prefemoral fossa shows a mixed echogenicity mass with anechoic cystic components in the right aspect of the coelom displacing normal coelomic structures. (C) Computed tomography image shows a 10-cm-diameter, soft tissue mass (circle) in the right caudal coelomic cavity. (D) After removal from the body cavity, the exteriorized mass is bilobed, pale tan, and firm. Renal and neoplastic tissue cannot be differentiated on gross exam. Scale bar, 5 cm.
(A) The cytologic preparation has aggregates of round to polygonal cells with a small to moderate nuclear to cytoplasmic ratio, small amount of pale blue cytoplasm, and round to oval nuclei with coarse chromatin. There is occasional rosette formation with central eosinophilic material (inset, arrow). Fine-needle aspirate cytology; Diff quick stain; scale bar 150 µm; inset scale bar, 25 µm. (B) This densely cellular neoplasm is composed of 60% blastema (asterisks), 30% tubules (arrows), 5% primitive glomeruli, and 5% mesenchyme. Hematoxylin and eosin stain; scale bar, 400 µm. (C) Blastema (asterisks) is composed of densely packed streams of blastemal cells that have indistinct borders, a small amount of pale eosinophilic cytoplasm, and oval, centrally located nuclei with clumped chromatin and occasionally evident nucleoli. Tubules frequently occur in clusters surrounded by blastema and are composed of a single layer of cuboidal to columnar epithelial cells with a moderate amount of pale eosinophilic cytoplasm, round to oval nuclei with stippled chromatin, and one small nucleolus. Primitive glomeruli (arrow) are clustered with tubules and are composed of tufts of cells projecting into lumina. Glomerular tufts are composed of cells with a high nuclear to cytoplasmic ratio surrounding central, small-caliber blood vessels. Hematoxylin and eosin stain; scale bar, 150 µm. (D) Immunohistochemistry for cytokeratins reveals strong, cytoplasmic immunoreactivity within tubules. Surrounding blastemal and mesenchyme are negative for immunoreactivity. AE1/AE3 immunohistochemistry; scale bar, 150 µm.
