Teratoma in the Cervical Spinal Cord of a Dog
An 11-year-old, spayed female giant schnauzer was presented for evaluation of chronic, progressive tetraparesis. Diagnostic imaging was consistent with intervertebral disk protrusion, and surgical decompression and stabilization were performed. Postoperatively the dog did not improve, and further imaging suggested an intramedullary mass at the level of the sixth cervical vertebra. The dog was euthanized 7 days after surgery, and a teratoma was found postmortem.
Introduction
Germ cell tumors are uncommon in small animals.1 Early in embryonal differentiation, the germ cells, which are found in the yolk sac, migrate to the gonadal ridge.2 Germ cell tumors are typically associated with the gonads; however, they may also occur in various other locations, such as the thymus, head, neck, and in the pineal, hypothalamic, or suprasellar regions of the brain.3,4 According to the World Health Organization classification, germ cell tumors affecting the central nervous system (CNS) may be classified as germinomas, embryonal carcinomas, yolk sac tumors, choriocarcinomas, teratomas, or mixed germ cell tumors.5
In teratomas, the germ cells have undergone somatic differentiation and have the potential to differentiate into the derivatives of all three germ layers (i.e., endoderm, mesoderm, ectoderm). In the past, the term “teratoid” was used for teratomas containing identifiable tissue from fewer than three germ layers.6 However, derivatives of one or two germ layers may overgrow the others, and it can be difficult to discern whether a particular tumor is teratoid or a true teratoma.7 Several theories exist regarding the formation of teratomas, with some controversy surrounding their development.8–11 One theory suggests that teratomas arise from multipotent germinal cells that are misplaced in early embryonic development. 12 Perhaps the best-accepted theory proposes that cells (possibly from the ectodermal Hensen’s node) escape primary inducer control during early embryonic development, detach, and grow elsewhere.7
In humans, CNS teratomas are rare, comprising 0.5% to 2.2% of all brain tumors and 0.2% to 0.5% of all spinal cord tumors.13–17 Few reports exist of CNS teratomas in dogs. Two dogs have been reported with an intracranial teratoma.18,19 A medulloepithelioma with teratomatous elements has been reported in the spinal cord of one dog.20 The purpose of this report is to describe a teratoma in the cervical spinal cord of a dog.
Case Report
An 11-year-old, 33-kg, spayed female giant schnauzer was presented with a 6-week history of progressive ataxia, tetraparesis, and neck pain. The ataxia was initially noted in the pelvic limbs, and it progressed to involve the thoracic limbs over a 2-week period. Clinical signs improved substantially with administration of dexamethasonea (0.25 mg/kg intravenously [IV] once), followed by carprofenb (dose unknown) by the referring veterinarian, but signs recurred. Several episodes of neck pain and right thoracic limb lameness were reported during the previous 2 years.
On admission, the dog had nonambulatory tetraparesis and was laterally recumbent, but she was alert and responsive. Mentation, cranial nerve examination, and segmental spinal reflexes were normal. A crossed extensor reflex was noted in all four limbs. When supported, proprioceptive deficits were present in all four limbs, and pain was noted on palpation of the cervical spine.
The clinical examination suggested a cervical myelopathy (first cervical [C1] to fifth cervical [C5] spinal cord segments). The history of intermittent thoracic limb lameness coupled with neck pain was interpreted as root signature, so a lesion affecting the caudal cervical spinal cord (sixth cervical [C6] to eighth cervical [C8] spinal cord segments) could not be ruled out. The differential diagnoses included caudal cervical spondylomyelopathy, intervertebral disk disease, neoplasia, meningomyelitis, and diskospondylitis.
A complete blood count (CBC) revealed a mild hypochromic, regenerative anemia (hematocrit 33%, reference range 37% to 54%; hemoglobin 11.3 g/dL, reference range 13 to 19.4 g/dL; 267,000/μL reticulocytes, reference range >60,000/μL). A serum biochemical profile showed an elevated alkaline phosphatase (2548 IU/L; reference range 14 to 126 IU/L). Thoracic radiographs revealed spondylosis deformans of the caudal thoracic vertebrae, but other structures were normal. Abdominal ultrasonography was unremarkable. Moderate numbers of rod-shaped bacteria were noted on urinalysis, and aerobic culture revealed heavy growth of Enterococcus spp.
Survey radiographs of the cervical spine demonstrated a proliferative osseous reaction around the articular facets at C5 to C6 and C6 to the seventh cervical vertebra (C7); dorsal displacement (“tipping”) of the cranial aspects of the C5 and C6 vertebral bodies; and mild narrowing of the intervertebral disk space at C6 to C7. Analysis of cerebrospinal fluid (CSF) collected from the cerebellomedullary cistern was normal. An iodinated contrast agentc was injected into the subarachnoid space between the fifth and sixth lumbar (L5 and L6) vertebrae. Myelography revealed ventral extradural compression of the spinal cord over the C6 to C7 space, consistent with intervertebral disk protrusion [Figures 1A, 1B]. Attenuation of the ventral and dorsal contrast columns within the subarachnoid space was noted from the C5 to C6 disk space caudally to the middle of the body of C6. These changes were consistent with decreased CSF flow from an extramedullary compressive lesion or an intramedullary process such as spinal cord swelling or neoplasia. Unfortunately, dynamic myelographic views were not obtained, and advanced diagnostic imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) was not available.
Decompression of the cervical spinal cord was performed at the C6 to C7 disk space via diskectomies at C5 to C6 and C6 to C7 and removal of the dorsal longitudinal ligament over C6 to C7. The spinal cord appeared normal. The disk spaces were distracted and fused with cortical bone allografts,d cancellous bone chips,e and a single cancellous screwf at each site. Surgical closure was routine, and postoperative radiographs confirmed adequate placement of the implants.
Recovery from anesthesia was unremarkable. Postoperatively, the dog remained nonambulatory, but voluntary motor activity was present. Although improvements in cervical mobility were noted, the dog’s overall neurological status did not change significantly over the next week. Cervical spinal radiographs and myelography were repeated, and additional electrodiagnostic tests were performed 7 days after the surgery. Electromyography revealed fibrillation potentials and positive sharp waves in numerous muscles of the thoracic and pelvic limbs. Motor nerve conduction velocity of the sciatic-tibial nerve was reduced (32.4 meters per second distally, 38.0 meters per second proximally; reference range 46 to 74 meters per second) and showed polyphasic, compound muscle action potentials. 21 These changes were consistent with a polyneuropathy.
Myelography was similar to the previous study, although the attenuation of the subarachnoid contrast column from the caudal aspect of C5 to the middle of the body of C6 was more evident and suggestive of an expansile intramedullary lesion. Ventral, extradural compression over the C6 to C7 disk space was still evident [Figures 2A, 2B]. The dog was euthanized, and a necropsy was performed.
Gross pathological examination revealed an expansile, nonencapsulated, moderately well-demarcated mass compressing the right ventrolateral aspect of the spinal cord at C6. The mass was similar in color to the dura mater and was visible in an extradural location, but it appeared to invade the dura and spinal cord. Histologically, the mass was composed of well-differentiated adipose tissue; interwoven bundles of mesenchymal cells; and scattered, small acinar structures filled with pale, eosinophilic, homogenous material [Figure 3]. These mesenchymal cells and acinar structures were embedded in small to moderate amounts of coarsely fibrillar and occasionally densely hyaline (osteoidlike) eosinophilic stroma. Mesenchymal cells were spindleshaped with moderate amounts of peripherally attenuated eosinophilic cytoplasm that merged with surrounding stroma. Acinar structures were lined by cuboidal to short columnar epithelial cells with modest amounts of eosinophilic cytoplasm [Figure 4]. Nuclei were oval to irregular, with vesicular chromatin and one to two round, well-demarcated, basophilic nucleoli. Mitotic figures ranged from zero to three per high-power field (hpf) and averaged one per five hpf. Throughout the mass were scattered, small, vascular spaces lined by plump endothelia, with intimal collections of spindle to polygonal cells [Figure 5] exhibiting occasional mitotic figures. Small numbers of lymphocytes and plasma cells were scattered throughout the tissue.Adjacent spinal cord had marked neuronal necrosis and locally extensive neuroaxonal degeneration. No histologically identifiable dura surrounded the mass or separated it from the spinal cord parenchyma. These findings were compatible with a teratoma of the cervical spinal cord.
The radial nerve and triceps muscle were also examined histologically. The radial nerve had areas of rare, dilated myelin sheaths and degenerated axons [Figure 6].Within the triceps muscle, occasional atrophied myofibers of angular shape were noted [Figure 7]. These changes were consistent with a neuropathy and associatedmuscle denervation. Special staining of muscle and nerve samples was not performed.
Discussion
The presence of ventral, extradural spinal cord compression at the C6 to C7 intervertebral space led to the original diagnosis of intervertebral disk disease, which complicated the management of this case. The signalment, history, and clinical signs were consistent with intervertebral disk disease, and an intramedullary neoplasm was considered less likely because the dog was painful. Osseous proliferation of the articular facets at C5 to C6 and C6 to C7 also increased the suspicion of cervical instability in this dog and contributed to the decision to surgically stabilize these two sites. At necropsy, the mass was grossly visible outside of the dura. Unfortunately, the extradural component of the tumor was lateralized and similar in appearance to dura and was not visualized at surgery. Histopathologically, the mass effaced the dura and invaded the spinal cord parenchyma, which explained the combination of extradural and intramedullary lesions seen on myelography.
This case illustrates some of the difficulties that may be associated with myelographic interpretation. Compressive spinal lesions are usually described by their position relative to the spinal cord and dura (i.e., extradural, intraduralextramedullary, or intramedullary).22 This classification has diagnostic value, as intramedullary and intraduralextramedullary lesions are often associated with neoplastic lesions, while extradural lesions are commonly associated with intervertebral disk disease and caudal cervical spondylomyelopathy. 23 Errors in myelographic interpretation can occur, however.22 The intramedullary changes seen on the initial myelogram in this case were mistakenly attributed to poor contrast visualization from external pressure and spinal cord edema and swelling, which are common with intervertebral disk disease. Poor contrast visualization in ventrodorsal views of the caudal cervical region, as seen in this case, is a frequent limitation of myelographic imaging.24,25
Advanced imaging procedures such as CT and MRI would have been very useful in the diagnosis and subsequent management of this case. Such imaging modalities were unfortunately unavailable for this dog, but they are routinely used to image the CNS of small animals. As teratomas typically contain areas of fat, calcification, and cystic fluid, they often have a heterogenous appearance with these imaging techniques.6,7 Contrast enhancement is typically heterogenous.6
In dogs, primary intracranial germ cell tumors have been reported, including two teratocarcinomas, seven malignant germ cell tumors, two craniopharyngiomas, an unclassified germ cell tumor, and a germinoma.18,19,26–30 Metastatic intracranial germ cell tumors have also been reported and included an ovarian dysgerminoma and a seminoma.31,32 These tumors occurred most commonly in the pineal gland and suprasellar regions, and presenting signs in these dogs included visual deficits, lethargy, anorexia, and endocrine abnormalities.18,19,26–32 In contrast, this animal was presented with chronic progressive tetraparesis and intermittent thoracic limb lameness primarily because of the location of the tumor in the cervical spinal cord. A medulloepithelioma with teratomatous elements has been reported in the spinal cord of one dog.20 Tissues from two germ cell layers were present, similar to the dog reported here. In contrast to the present case, the dog in the previous report was young, and the tumor was located in the thoracolumbar spinal cord.20 A mixed germ cell tumor has been reported in the spinal cord of a dog.33 This dog was young, in contrast to the present case. The dog was presented for paraplegia, and the mass was located at the L6 to seventh lumbar (L7) spinal cord segment. The mass was defined as being subdural with extra- and intramedullary components.
Electrodiagnostic testing and histopathological analyses of nerve and muscle samples in this dog were consistent with a polyneuropathy. Polyneuropathies typically are presented with progressive paraparesis or tetraparesis, as seen in this case. However, the dog in this report had normal segmental spinal reflexes, which are typically reduced with neuropathic disease.34 Polyneuropathies can have a variety of etiologies, such as metabolic, infectious, immune-mediated, toxic, and paraneoplastic disorders.35 Although the cause of the polyneuropathy was undetermined in this case, infectious and toxic causes were considered unlikely, and some metabolic diseases (e.g., diabetes mellitus) were ruled out, making paraneoplastic disease more likely. Polyneuropathies have been described in association with a number of different tumors in a variety of locations.36–43 Neurological improvement following therapy for the neoplastic disease has occasionally been reported.37,42 The extent to which the polyneuropathy contributed to this dog’s clinical signs was unclear, as subclinical electrodiagnostic and histopathological changes are often seen in animals with neoplasia in remote locations.39,40,43 Additional electrodiagnostic testing was performed in this case because of the dog’s failure to improve after decompressive surgery and a growing suspicion of a neoplastic process affecting the spinal cord.
Conclusion
A teratoma of the cervical spinal cord was diagnosed in an 11-year-old giant schnauzer. Ventral, extradural compression noted on initial myelography of the cervical spinal cord led to the original diagnosis of intervertebral disk disease, which complicated the management of this case. Gross and microscopic pathological analyses showed that the mass effaced the dura and was present in intradural and extradural locations. Teratomas should be considered in the differential diagnosis of compressive spinal cord lesions in dogs of any age.
Dexamethasone; Phoenix Scientific, Inc., St. Joseph, MO 64503
Rimadyl; Pfizer Animal Health, Exton, PA 19341
Omnipaque; Amersham Health, Princeton, NJ 08540
Osteo-Allograft; Veterinary Transplant Services, Kent, WA 98032
Cancellous bone chips; Veterinary Transplant Services, Kent, WA 98032
Cancellous bone screw; Synthes USA, Westchester, PA 19380
Acknowledgments
The authors thank Dr. Craig Clifford for assistance in preparing this manuscript.
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Citation: Journal of the American Animal Hospital Association 43, 5; 10.5326/0430292
Lateral (A) and ventrodorsal (B) cervical myelogram of an 11-year-old, spayed female giant schnauzer presented for nonambulatory tetraparesis. Ventral extradural compression is present at the sixth to seventh cervical (C6 to C7) intervertebral disk space (arrow), and a thinning of the ventral contrast column can be seen from the fifth cervical (C5) to C6 intervertebral disk space caudally to the middle of the body of C6 (arrowheads). T1=first thoracic vertebra; R=right.
Lateral (A) and ventrodorsal (B) cervical myelogram of the dog in Figure 1, taken 7 days after surgery. Ventral extradural compression at the C6 to C7 intervertebral space (arrow) and thinning of the ventral contrast column persist (arrowheads). Cancellous bone screws and cortical allografts are present.
Histopathological section of the mass in the cervical spinal cord from the dog in Figure 1, removed at necropsy. The expansile mass is composed predominantly of well-differentiated adipose tissue (arrow) compressing the spinal cord (arrowheads) (Hematoxylin and eosin stain; bar=1.0 mm).
Histopathological section of the mass, showing vascular spaces lined by plump endothelia (arrows) with intimal proliferations of spindle to polygonal cells (arrowheads) (Hematoxylin and eosin stain; bar=50 μm).
Histopathological section of the radial nerve of the dog in Figure 1, showing dilated axon sheath (arrow) containing a single macrophage (arrowhead), indicating mild axonal degeneration (Hematoxylin and eosin stain; bar=50 μm).
Histopathological section of the triceps muscle from the dog in Figure 1, showing angular myofibers (x) and a fragmented, homogenous myofiber lacking striations (arrow) intermixed with modest numbers of macrophages (arrowhead) (Hematoxylin and eosin stain; bar=50 μm).
