1-year-old intact male Argentinian Mastiff dog, (Canis familaris).

Gross Description:  

Over the dorsal vertebral processes, centered on the thoracolumbar junction, is a 12 cm long incision that is closed with surgical staples. Subcutaneous tissue deep to the incision is dark red and contains large aggregates of friable, dark red material (clot, fibrin). The right dorsal pedicles and lamina of the lumbar vertebrae 1 and 2 are absent (surgical artifact), and the surrounding tissue is dark red. Dura overlying the mass is mostly intact with a single small defect (surgical artifact). At the level of L1-L2, the spinal cord is moderately enlarged and dark brown to red. Protruding from subdural space into the spinal cord is a 1 cm diameter, well-demarcated, soft, white mass. The tissue immediately surrounding the mass is markedly expanded by abundant dark red material (hemorrhage).

Histopathologic Description:

Spinal cord, L1- L2: Expanding from within and beneath the dura and infiltrating the underlying spinal cord is a densely cellular, well-demarcated, partially encapsulated neoplasm. Neoplastic cells are of two distinct cell populations. One population forms tubules lined by cuboidal cells that have a small amount of eosinophilic cytoplasm and a single round nucleus with finely stippled chromatin. Surrounding the neoplastic tubules are sheets of polygonal blastemal cells that have minimal cytoplasm and a round, deeply basophilic nucleus with slight vesicular chromatin. The mitotic rate is high with 25 mitoses in 10 highpowered fields. Surrounding the neoplasm is abundant hemorrhage that extends cranially and caudally, obliterating large portions of the spinal cord and surrounding few remaining neurons. Scattered throughout the areas of hemorrhage are few small aggregate of neutrophils. Cranial and caudal to the mass, white matter tracts are markedly vacuolated with many spheroids. Immunostaining of the mass demonstrates that neoplastic epithelial cells are immunoreactive on staining with cytokeratin and mesenchymal cells are immunoreactive on staining with vimentin. Neoplastic cells are not immunoreactive on staining with neuron specific enolase or glial fibrillary acidic protein.

Morphologic Diagnosis:  

Spinal cord, L1-L2: Nephroblastoma.



Contributor Comment:  

Spinal nephroblastomas occur in young dogs, and German Shepherds may be overrepresented.2 These neoplasms typically arise at the thoracolumbar junction and are thought to arise from ectopic rests of embryonal renal tissue entrapped in the subdural space.2 Metastasis is not typical4 though possible intraspinal metastasis has been reported.5 Affected animals typically present with hindlimb ataxia, paresis, and proprioceptive deficits.4,5 The classic histomorphology of spinal nephroblastoma is similar to that of renal nephroblastoma. Neoplastic cells form embryonic glomeruli, primitive tubules, and primitive acini, surrounded by a mesenchymal stroma.2 Cytologic evaluation shows a characteristic triphasic pattern with mesenchymal cells, epithelial cells, and undifferentiated hyperchromatic cells.1 The submitted neoplasm demonstrates characteristic primitive tubules, acini, and mesenchymal stroma, though it lacks classic embryonic glomeruloid structures. Differential diagnoses include ependymoma, primitive neuroectodermal tumor, or poorly d i f f e r e n t i a t e d a s t r o c y t o m a . 5 Immunohistochemistry can aid in establishing a definitive diagnosis. The epithelial cells within spinal nephroblastomas are immunopositive for cytokeratin, and the blastemal cells and stroma are immunopostive for vimentin.2,5 The neoplastic cells are immunonegative for NSE, GFAP, neurofilament, or chromogranin.2,5 In a d d i t i o n , t h e s e n e o p l a s m s m a y b e i m m u n o p o s i t i v e o n s t a i n i n g w i t h a nephroblastoma-specific marker, Wilm’s tumor gene protein product (WT1).3 Immunostaining of this neoplasm was consistent with spinal nephroblastoma; immunostaining for Wilm’s tumor gene protein product was not performed.

JPC Diagnosis:  

Spinal cord: Nephroblastoma.

Conference Comment:  

Nephroblastoma, also known as Wilms’ tumor, is an important human pediatric neoplasm. The term ‘‘blastoma’’ defines the neoplastic population as embryonic, rather than mature terminally differentiated cells; histologically, nephroblastoma recapitulates the embryologic development of the kidney.1 The protein product of the Wilms’ tumor suppressor gene-1 (WT-1) is a DNA binding protein important in normal renal development; inactivation of this gene likely prevents differentiation of primitive metanephric cells and i s d o c u m e n t e d i n s o m e p e d i a t r i c nephroblastomas.3 A similar intradural extramedullary spinal cord neoplasm occurs between the tenth thoracic (T10) and second lumbar (L2) spinal cord segments in large breed dogs, typically less than three years old, and is thus referred to as thoracolumbar spinal tumor of young dogs.5 Although the histogenesis of this tumor has not been firmly established, it is thought to originate from ectopic metanephric blastema trapped between the dura and the developing spinal cord.5 The Wilms’ tumor gene protein product, WT1, has been identified immunohistochemically in some of these “canine spinal cord nephroblastomas.”3 As noted by the contributor, the microscopic features (a poorly differentiated blastemal component, mesenchymal stroma, and an epithelial component forming tubules and vague glomeruloid structures) and immunohistochemical staining characteristics (cytokeratin positive epithelial cells and vimentin positive blastemal and mesenchymal cells) in this case are consistent canine spinal cord nephroblastoma (or perhaps more accurately, thoracolumbar spinal tumor of young dogs); however, there is significant slide variation and tissue identification for some conference participants was difficult, as some sections did not contain any identifiable spinal cord.


1. De Lorenzi D, Baroni M, Mandara MT. A true "triphasic" pattern: thoracolumbar spinal tumor in a young dog. Vet Clin Pathol. 2007;36:200-203. 2. Meuten DJ. Tumours of the urinary system. In: Meuten DJ, ed. Tumors in Domestic Animals. Ames, IA: Iowa State Press; 2002:519-520. 3. Pearson GR, Gregory SP, Charles AK. Immunohistochemical demonstration of Wilms tumour gene product WT1 in a canine "neuroepithelioma" providing evidence for its classification as an extrarenal nephroblastoma. J Comp Pathol. 1997;116:321-327. 4. Summers BA, deLahunta A, McEntee M, Kuhajda FP. A novel intradural extramedullary spinal cord tumor in young dogs. Acta Neuropathol. 1988;75:402-410. 5. Terrell SP, Platt SR, Chrisman CL, Homer BL, de Lahunta A, Summers BA. Possible intraspinal m e t a s t a s i s o f a c a n i n e s p i n a l c o r d nephroblastoma. Vet Pathol. 2000;37:94-97.

Click the slide to view.

3-1. Spinal cord

3-2. Spinal cord

3-3. Spinal cord

3-4. Spinal cord

3-5. Spinal cord

3-6. Spinal cord

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