Extradural Spinal, Bone Marrow, and Renal Nephroblastoma

Case Report

A 6.6-kg, 1-year-old, female intact Shetland sheepdog was referred to the Emergency Service at the Veterinary Hospital of the University of Pennsylvania (VHUP) for nonambulatory paraparesis. She was first noticed to be abnormal 5 days prior to presentation when she became incoordinated after playing with her canine housemate. The next day, her neck was stiff and maintained in an extended position, and she was unsteady in the pelvic limbs. She was taken to her local veterinarian who reported conscious proprioceptive deficits in the pelvic limbs (worse in the left limb than the right), hind-limb ataxia, and reluctance to lower her head. Cervical and thoracolumbar radiographs were unremarkable. She was started on prednisone (10 mg [1.5 mg/kg body weight] per os [PO] bid for 3 days, then sid for 5 days) and methocarbamol (125 mg [19 mg/kg body weight] PO tid for 5 days). Restricted activity was recommended for 2 weeks. Three days later, the dog had progressive pelvic-limb paresis and acute onset of urinary and fecal incontinence. Examination revealed conscious proprioceptive deficits in the pelvic limbs and an inability to stand without support. A complete blood count (CBC) showed a stress leukogram but was otherwise unremarkable. Results from a serum biochemistry profile were within reference ranges. Due to the progression of the pelvic limb deficits and incontinence, the dog was referred to VHUP for further neurological evaluation.

Neurological examination revealed a dull dog that was not willing to ambulate. She sat with her pelvic limbs extended and hips flexed. When assisted to walk, she crossed midline, interfered with the pelvic limbs, and was slightly short-strided in the thoracic limbs. She had no postural ability in the pelvic limbs (based on proprioception, hopping, extensor postural thrust testing). She was slightly weak when wheel-barrowed. Reflex examination showed mildly depressed sciatic reflexes (i.e., gastrocnemius, cranial tibial) and crossed extension in the pelvic limbs. There was increased tone in the flexors of the hips and extensors of the stifles. There was no tail or anal tone, and the perineal area was anesthetic. The bladder was normal size on palpation and easy to express. She resented movement of her neck in any direction and was painful on palpation over the lumbosacral junction. Generalized muscle atrophy was present. Cranial nerve and ocular fundic examinations were normal. Multifocal neurological disease was suspected with the lesions involving the cervical spinal cord and lumbar intumescence or cauda equina. Differential diagnoses included round cell or metastatic neoplasia; infectious disease (i.e., protozoal, tick-borne, fungal, viral, or bacterial infections); congenital, inherited, or degenerative disorder; traumatic or vascular event; or an inflammatory condition (i.e., granulomatous meningoencephalitis). Additionally, she was febrile (103.1°F) and tachycardic (180 beats per minute). Differential diagnoses for pyrexia and tachycardia included pain, infection, inflammation, or cancer. She had enlarged mammary veins with no prior breeding history, suspected due to decreased venous return. A nonpainful, mid-dorsal abdominal mass was found on abdominal palpation. Differential diagnoses for the abdominal mass included round cell or metastatic neoplasia, pyometra, endometritis, endometrial hyperplasia, or an ovarian cyst. When combining physical and neurological examination findings, infectious disease was thought to be less likely, but Cryptococcus infection remained a remote possibility.

The CBC revealed a leukocytosis (19.3 × 10³/μL; reference range, 6.7 to 18.3 × 10³/μL) characterized by a mature neutrophilia (14.0 × 10³/μL; reference range, 3.6 to 12.5 × 10³/μL) and monocytosis (3.9 × 10³/μL; reference range, 0.1 to 1.5 × 10³/μL) consistent with a stress leukogram. The erythrogram was unremarkable. An initial thrombocytopenia (123 × 10³/μL; reference range, 175 to 400 × 10³/μL) was not substantiated upon evaluation of a second blood sample later that day (198 × 10³/μL). Total protein concentration measured via refractometer was increased (9.7 g/dL; reference range, 6.0 to 8.6 g/dL).

Abnormalities on the serum biochemistry profile included hyperproteinemia (7.5 g/dL; reference range, 4.8 to 6.2 g/dL) attributable to mild hyperglobulinemia. The serum alkaline phosphatase (162 U/L; reference range, 20 to 155 U/L) was mildly increased, likely as a result of corticosteroid administration. Aspartate aminotransferase concentration was increased (72 U/L; reference range, 1 to 37 U/L), although there were no other abnormal hepatic indices, and the creatine kinase concentration was within the reference range. Additional abnormalities included a mild hypochloridemia (107 mmol/L; reference range, 110 to 118 mmol/L) and an increased anion gap (22 mmol/L; reference range, 12 to 16 mmol/L), most likely due to an increased lactate (3.3 mmol/L; reference range, 0.6 to 2.5 mmol/L). The urinalysis (via cystocentesis) revealed a urine specific gravity of 1.039 with proteinuria (3+) and hemoglobinuria (3+) attributable to hematuria (red blood cells, 100 to 120 per high-power field). The hematuria was suspected to be the result of contamination from the sampling method. The urine sediment was otherwise unremarkable. There was no growth on urine culture.

Chest radiographs (right lateral, left lateral, and ventrodorsal views) were unremarkable. Radiographs of the dog’s abdomen (left lateral and ventrodorsal views) showed a large abdominal mass. The origin of the mass was suspected to be the right kidney based on displacement of the gastrointestinal tract and left kidney [Figure 1]. There were no detectable radiographic abnormalities along the spine as visualized on the chest and abdominal radiographs (midcervical to caudal lumbar spine). An abdominal ultrasound revealed an extensive soft-tissue mass (approximately 6.4 × 5.4 cm) of undetermined origin. The mass was mixed in echogenicity filling the cranial abdomen, located between the left kidney and the liver. The spleen, right kidney, both adrenal glands, uterus, and ovaries were not visualized ultrasonographically because of the distortion of the abdomen from the mass. The caudal vena cava had normal blood velocity and cranial flow. The liver, gall bladder, left kidney, urinary bladder, pancreas, lymph nodes, and gastrointestinal tract appeared normal ultrasonographically.

A fine-needle aspirate for cytopathology of the abdominal mass was obtained. The cytopathology consisted of numerous, large (12 to 14 μm in diameter) round cells noted individually and in clusters [Figure 2]. These cells had round to oval nuclei with a finely granular chromatin, single to multiple small nucleoli, and scant rim of basophilic cytoplasm [Figure 3]. The cytopathology was interpreted as malignant neoplasia. Cellular morphology was most suggestive of lymphoma; however, the cohesive tendency of the cells argued against a lymphoid origin. Given the age of the dog and location of the mass, nephroblastoma was included as a second differential interpretation.

A bone-marrow aspirate was next obtained due to the possibility of lymphoma and in an effort to stage disease, and cytopathology revealed a large number of infiltrating blasts with lymphoid morphology [Figure 4]. The blasts were noted individually and in large clusters and were identical to those described in the abdominal mass cytology. In light of the bone-marrow aspirate cytology, the behavior of the neoplasm supported a cytopathological interpretation of lymphoma rather than nephroblastoma in spite of the cohesive nature of the cells.

A coagulation panel evaluating prothrombin time, activated partial thromboplastin time, and fibrin degradation product concentration, which was performed prior to biopsies of the abdominal mass, was normal. Multiple ultrasound-guided trephine biopsies of the abdominal mass were obtained. Histopathological results were available 2 days later. The trephine biopsies were compatible with nephroblastoma. The sections contained adipose tissue, bands of fibrous connective tissue, and islands of neoplastic cells. The tumor cells varied in morphology from ovoid to fusiform and were interspersed with bands of fibrous connective tissue.

The next day, a cerebellomedullary cisternal tap was performed under general anesthesia. Cerebrospinal fluid (CSF) nucleated cell count and protein concentration were unremarkable (0 nucleated cells/μL; reference range, 0 to 5; protein, 19 mg/dL; reference range, <25 mg/dL). Evaluation of a cytospin preparation of the CSF was also unremarkable (one nondegenerate neutrophil, six lymphocytes, and 83 monocytoid cells). Pandy test was negative. Although unlikely, a Cryptococcus neoformans agglutination test was performed on the CSF (because of the neurological manifestations of disease) and was negative.

During diagnostic testing and hospitalization, supportive care was given and serial neurological examinations were performed. There was no change (i.e., improvement or progression) in the dog’s neurological examination. Pending test results, no medical therapy was initiated.

The owner elected humane euthanasia and requested a postmortem examination. Immediately following euthanasia, a computed tomography (CT) scan of the dog’s spine and abdomen was performed (for clinical interest) to evaluate if this imaging modality would better characterize the neurological and physical lesions. In the right dorsal cranial abdomen, there was a multilobulated mass that appeared contiguous with several intra-abdominal organs including the caudate lobe of the liver, the pancreas, lymph nodes, and possibly the uterus, ovaries, or both. No distinction could be seen between the mass and the hypaxial musculature at certain levels (in the lumbar region) along the spine because of the extensive nature of the mass. The right kidney could not be positively identified, and it was probably involved in the mass. A CT scan of the thoracolumbar spine (5-mm slices at 5-mm intervals) showed no vertebral or spinal cord abnormalities; however, no intrathecal or intravenous contrast was administered.

At gross necropsy, the dog’s body tissues were icteric, despite a normal total bilirubin on her serum biochemistry profile 3 days prior to euthanasia. The dorsal abdominal cavity contained an irregular, multilobulated, smooth-surfaced, soft mass that bulged on cut section and was mottled pale yellow and red. It extended from the diaphragm to the level of the fourth lumbar vertebra and involved the right kidney, the adrenal glands, the pancreas, duodenum, portal vein, caudal vena cava, and abdominal aorta. The duodenum and pancreas were firmly adhered to the mass, and a large part of the right kidney parenchyma was replaced by it, including the papilla, cranial pole, and hilus [Figure 5]. The left adrenal gland was on the dorsal midline, the abdominal aorta was entrapped within the mass, and the caudal vena cava coursed over its dorsal surface. The lumen of the caudal vena cava was filled with pale yellow, soft material similar to the mass. The spleen, liver, and ovaries were grossly unaffected. The liver was enlarged, weighing 279.1 g (4.2% of body weight; reference range, 3.2% to 3.7%). Adjacent to the right side of the third and fourth lumbar vertebrae within the spinal canal, there was a pink/tan, soft, irregular, extradural mass measuring 2.5 cm in length and 1.1 cm in diameter [Figure 6]. The vertebrae were grossly normal, and the mass was not adhered to the vertebrae. All other parts of the spinal cord and the brain were grossly normal.

On histopathology of the kidney, the neoplasm replaced a large part of the normal parenchyma and consisted of a nonencapsulated, multilobulated, poorly differentiated, expansile mass. Within the lobules, cells were arranged into packets and nests by thin trabeculae of fibrous connective tissue [Figure 7]. Individual cells were primitive with sparse amounts of cytoplasm, discrete cell borders, and centrally to eccentrically placed, oval to round, densely hyperchromatic nuclei. Some nuclei had a coarse chromatin pattern, mostly without distinct nucleoli, and the mitotic index averaged 4 to 5 per 40× field. There were areas of necrosis and hemorrhage within the neoplasm. Morphologically identical cells invaded the lumen of the caudal vena cava, effaced and expanded the left adrenal gland and hepatic and mediastinal lymph nodes, and infiltrated small areas of the pulmonary interstitium.

Cells morphologically identical to those found in the kidney and abdomen were also demonstrated in the third and fourth lumbar vertebrae, where they filled the marrow cavity, effaced the periosteum of the spinal canal, and extended into the extradural spinal canal to compress the spinal cord [Figure 8]. There was mild to moderate Wallerian degeneration (consisting of multifocal myelin sheath distension, axonal swelling, and myelomacrophages) in the ventral, lateral, and dorsal funiculi of spinal cord at the level of the third and fourth lumbar vertebrae. There was no direct continuation between the abdominal mass and the vertebrae, and the skeletal muscles surrounding the vertebrae did not contain neoplastic tissue. Most segments of the cervical and thoracic spinal cord were evaluated histologically, and no neoplastic tissue was identified.

The mass in the kidney was selected for immunohistochemistry. The majority of the neoplastic cells reacted strongly to antibody against the mesenchymal marker vimentin, but none of the cells within the neoplasm reacted with the antibodies against epithelial markers AE1/AE3, Cam 5.2, or Multi-CK; B-cell marker BLA.36; or T-cell marker CD3.

Discussion

Nephroblastoma (also known as embryonal nephroma, embryonal adenosarcoma, and Wilms’ tumor) is rare in dogs and cats, but more common in pigs and chickens.¹ In children, Wilms’ tumor is the most common primary renal tumor and the second most common solid abdominal tumor.² In dogs, nephroblastoma usually involves one kidney or the spinal cord, but not both. For both the renal or spinal cord form, young intact dogs are most commonly affected, with no apparent breed or sex predilection. Most tumors are malignant. The origin of the tumor is thought to be embryonic tissue or metanephric blastema, persisting in a primitive state without fully differentiating into functional tissue. Primary spinal nephroblastoma is thought to arise from embryonic tissue entrapped within the dura during fetal development. Because there is a range of tissue differentiation (composed of blastemal, stromal, and/or epithelial units), the histopathological appearance of the neoplasm can vary in each case. In humans, the more differentiated the tumor, the better the response to therapy and prognosis.²

Clinical signs in dogs with nephroblastoma are dependent on tumor location. In dogs with primary spinal nephroblastoma, the clinical signs are consistent with a spinal cord lesion between the third thoracic and third lumbar spinal cord segments. The most common neurological finding is pelvic-limb paresis and ataxia. Typically the lesion is intradural and extramedullary, involving the tenth thoracic to the second lumbar spinal cord segments.^3–11 There have been rare reports of intramedullary nephroblastoma at these spinal cord segments.¹²¹³ This dog had extradural spinal cord compression at the level of the lumbar intumescence and consequently had urinary and fecal incontinence, loss of tail and anal tone, and perineal analgesia. Spinal cord nephroblastoma has not been documented to metastasize. However, a 2-year-old, female intact basset hound was found to have two spinal nephroblastoma tumors (with one more differentiated than the other), which supported metastasis within the spinal cord.⁸ Similar to renal nephroblastoma, clinicopathological findings are generally unremarkable. Survey radiology of the spine often shows no significant abnormalities. In all cases of extramedullary nephroblastoma, myelography should better localize and characterize the lesion.

In dogs with renal nephroblastoma, the most frequently reported clinical signs include abdominal distension, a palpable abdominal mass, lethargy, anorexia, emaciation, and hematuria. About 65% of the cases have metastatic disease, with the lungs being the most common site of metastasis.¹⁴ Other sites of metastasis have included the adrenals, opposite kidney, lymph nodes, thymus, liver, thyroid, and in one case report, bone (i.e., tibia).¹⁵ Local invasion or extension of the tumor through the renal capsule may lead to omental, mesenteric, or caudal vena caval involvement. Clinicopathological findings are generally unremarkable. Abdominal radiographs often localize the mass to the region of the kidneys.

This report represents unique clinical and pathological manifestations of nephroblastoma. The dog’s history and clinical signs demonstrated acute neurological disease, and her physical examination revealed an intra-abdominal mass as well as multifocal neurological disease. The tumor was found involving the right kidney, caudal vena cava, both adrenal glands, hepatic and mediastinal lymph nodes, pulmonary interstitium, bone marrow and periosteum of the third and fourth vertebrae as well as the extradural space of spinal canal at the same level, and the bone marrow. Direct extension of the abdominal mass to the spinal canal was not demonstrated, suggesting extradural spinal metastasis. It is also possible that this tumor did not metastasize from the kidney to the spinal region, but that these two locations represent primary nephroblastoma at both sites due to embryonic remnants remaining at both sites. Histopathology of portions of the spinal cord above the lumbar intumescence was unremarkable; however, the dog was short-strided in the thoracic limbs, had significant neck pain, increased tone in the pelvic limbs, and crossed extension in the pelvic limbs, all suggesting a lesion above the lumbar intumescence. These clinical signs remained unexplained. Importantly, bone-marrow aspirate revealed bone-marrow metastasis, which has not been reported in the literature, although one case report did involve extensive tibial nephroblastoma with invasion of the medullary cavity.¹⁵ The clinical and cytopathological findings in this dog supported a diagnosis of lymphosarcoma as well as nephroblastoma, with a stronger suspicion of lymphosarcoma because of bone-marrow involvement. To further rule out a diagnosis of lymphoma, polymerase chain reaction (PCR) of tumor tissue, bone marrow, and lymph nodes could have been considered to evaluate for presence or absence of B or T lymphocyte receptor rearrangement. Histopathology with immunohistochemistry confirmed a diagnosis of nephroblastoma in this case.

Immunohistochemistry has been used to identify the mesenchymal or epithelial components of nephroblastoma. Cytokeratin (an epithelial marker) and vimentin (a mesenchymal marker used to identify blastemal and stromal elements) immunoreactivity patterns in canine nephroblastoma reflect the varied composition of the tumor. The histogenesis of primary spinal nephroblastoma has not been definitively proven. Unless immunohistochemistry is utilized, the spinal cord form of nephroblastoma can be confused with neuroepithelioma, medulloepithelioma, or ependymoma because of the histopathological variation of the tissue and the tumor location.⁷ In dogs, immunohistochemistry has shown spinal nephroblastoma to stain negatively for the neuroectodermal marker, glial fibrillary acidic protein (GFAP), and occasionally faintly positively for a less specific neural marker, neuron-specific enolase (NSE), also seen in some human Wilms’ tumors.⁶ Nephroblastoma stains positively with mesenchymal or epithelial markers or both. In humans, an antibody to the Wilms’ tumor gene product (WT1), found on the human chromosome 11, has been useful in the diagnosis of nephroblastoma.⁶ The WT1 has also been demonstrated in a canine spinal nephroblastoma,⁶ but was not performed in this case because of test availability.

Treatment in human patients with renal nephroblastoma includes surgical resection, chemotherapy, and radiotherapy. The treatment protocol often depends on the stage of the tumor adopted by the National Wilms’ Study Group for humans.² Spinal nephroblastoma has not been seen in humans. In dogs with renal nephroblastoma, the treatment of choice is nephrectomy of the affected kidney. Because local invasion or distant metastasis is common, chemotherapy and radiotherapy have been documented in a few cases with variable success in prolonging survival rates. All of the dogs that received chemotherapy in addition to surgery died of eventual metastasis within weeks to months, except for one dog recently reported to remain disease free for over 25 months.¹⁷ In dogs with spinal nephroblastoma, surgical excision can lead to long-term resolution with limited morbidity.⁴⁵¹³ The prognosis for complete recovery is guarded to poor following surgical excision of the renal mass, although a recent report showed Stage I renal nephroblastoma has a more favorable prognosis with surgery and chemotherapy.¹⁷ The prognosis associated with surgery for spinal cord nephroblastoma is uncertain because of the few cases reported.

Conclusion

It is now apparent that a combination of neurological and abdominal diseases can be seen with nephroblastoma. Primary spinal nephroblastoma is not limited to intradural, extramedullary, or intramedullary involvement primarily at the tenth thoracic vertebrae to the second lumbar vertebrae, as previously reported. This tumor can metastasize to the bone marrow and spinal canal. In this case, spinal nephroblastoma was found in the bone marrow and periosteum of the third and fourth lumbar vertebrae and extradurally at the same level. This report documents potential clinical and pathological manifestations of canine nephroblastoma that have not been previously reported.

Acknowledgments

The authors thank Drs. Sheldon Steinberg and Charles Vite (Neurology Section, Department of Clinical Studies, Veterinary Hospital of the University of Pennsylvania) for review of this manuscript.