Abstract
A 1-year-old cat was presented with general discomfort but no neurologic deficits on physical examination. An extradural spinal cord compression at the level of T10–11 and T11–12 was evident on myelography and computed tomography examination. Hemilaminectomy was performed to decompress the spinal cord. Histopathology of the abnormal pedicle and lamina revealed vertebral angiomatosis. This rare vascular malformation was the cause of the spinal cord compression in this cat. It is seen in cats less than 2 years of age and affected the thoracic spine in all four previously reported cases.
A 1-year-old neutered male domestic shorthair cat was presented with a 6-week history of pain in the axillary and lumbar regions and general discomfort. Dexamethasone injections administered by the referring veterinarian resolved the clinical signs temporarily, but they reoccurred 9 days later. Physical examination showed pain upon palpation of the spine and on ventroflexion of the neck. Serological tests for toxoplasmosis and feline leukemia virus/feline immunodeficiency virus were negative. No abnormality was noted on complete blood count, chemistry panel, urinalysis and cerebrospinal fluid analysis. Anesthesia was induced using a combination of medetomidine (Dormitor; Pfizer, New York, USA) and ketamine (Vetaket; Lloyd Inc, Iowa, USA) and maintained with isoflurane (IsoFlo; Abbott Laboratories, Illinois, USA). All diagnostic procedures were undertaken during the same anesthetic episode, while the surgery was performed a day later using the same anesthetic protocol. No abnormal events or trends were reported during this period. The cat appeared stable during the whole time.
Survey radiographs of the spine showed an ill-defined sclerosis and new bone formation associated with the vertebral pedicle and body at the 11th thoracic vertebra on the left side in the ventrodorsal view (Fig 1). The cranial and caudal articular facet of T11 appeared mildly irregular on this side. A myelogram was performed by placing a 22 gauge spinal needle into the ventral subarachnoid space at L5/6 and injecting 0.25 ml/kg of 240 mgI/ml Iohexol (Omnipaque, General Electric (GE) Healthcare, Princeton, New Jersey (NJ)). A narrowing of the contrast column was observed ventrally at the level of T11–12 and dorsally within the vertebral body of T11 in the lateral view. On the ventrodorsal view, marked displacement of the left contrast column toward the midline within the vertebral body of T11 was noted (Fig 2). An extradural, focal left-sided spinal cord compression at T11 was diagnosed. Differential diagnoses included vertebral new bone formation due to old trauma, disc extrusion, cartilaginous exostoses, bone abscess, neoplasia, granuloma, old hematoma or migrating foreign body. In order to better define the lesion and to aid surgical planning, a post-myelographic computed tomography (CT) was performed.
Survey ventrodorsal view of the thoracolumbar spine: Notice the ill-defined and irregular new bone formation on the left lateral side of T11 (arrows).
Oblique ventrodorsal myelographic image of the thoracolumbar area: Note the marked deviation of the spinal cord to the right side with narrowing of the spinal cord within the vertebral body of T11.
Continuous transverse images with a slice thickness of 2 mm and a bone algorithm were acquired from T9 through T13 using a single slice helical scanner (Picker PQ 5000, Universal Medical Systems, Ohio, USA). A thinning of the contrast column with deviation of the spinal cord to the right side within the body of T11 was observed (Fig 3A). Marked thickening of the left pedicle of T11 with new bone formation involving the entire length of the vertebral body was noted. Some of its margins were irregular while others were smooth (Fig 3B). The new bone formation was accentuated laterally, but also involved the medial lamina and, therefore, resulted in a narrowing of the vertebral canal diameter and displacement of the spinal cord to the right side. Hyperdense material was seen within the intervertebral foramen and the vertebral canal at T11-T12 with an attenuation value of 680 Hounsfield units. In the normal adjacent bone, an attenuation value of 800 HU was measured. Considering the changes seen on CT, the lesion was considered to be most likely due to bony callus as a result of an old trauma or chronic infection. Malignant neoplasia was considered less likely due to the age of the animal and the lack of lysis. Congenital benign vascular malformation was not excluded as many skeletal neoplasms in cats are proliferative.
(A) and (B). Transverse CT images (bone window) of T11. The images were obtained following intrathecal injection of contrast medium. Note the markedly thickened lamina on the left side in comparison to the right with irregular new bone formation laterally. There is also hyperdense material within the vertebral canal causing marked deviation of the spinal cord to the right. The lamina was submitted for histopathology and found to be reactive bone.
The following day, a left-sided hemilaminectomy including the articular processes of T10–11 and T11–12was performed in order to explore and decompress the spinal cord. The surface of the cortex of the lamina and body of the vertebra was irregular and appeared to have proliferative new bone. The bone being burred away seemed to be of normal density. The hemilaminectomy site spanned the entire compressive region. Evaluation of the epidural space revealed the absence of epidural fat and the spinal cord was deviated to the right side. An autogenous fat graft obtained from the dorsal subcutaneous tissue was placed at the hemilaminectomy site followed by routine closure.
The lamina and several small fragments of bone were submitted for cytology, histopathology and culture/sensitivity. Cytological impression smears were of low cellularity, consisting of erythrocytes and few nucleated cells, including well-differentiated osteoblasts and osteoclasts, showing a poor degree of cellular preservation. No neutrophils or other inflammatory cells were observed. Histopathology revealed multifocal angiomas consisting of benign proliferations of well-differentiated, small caliber blood vessels throughout the medullary cavity, consistent with vertebral angiomatosis.
Medetomidine was reversed at the end of surgery with 0.0025 mg of atipamezole (Antisedan; Pfizer, New York USA). Postoperatively the cat was slow to recover from anesthesia with an uneventful extubation period. Three hours after surgery the cat experienced cardiorespiratory arrest. Cardiac function was re-established. After 2 h of manual ventilation, the cat did not regain spontaneous ventilation; the owners elected euthanasia without pursuing necropsy.
Several studies and case reports of specific disease processes affecting the spinal cord of cats have been published, including feline infectious peritonitis (FIP), lymphoma, intervertebral disk disease and vertebral column neoplasia as well as ischemia or infarct and trauma. 1–6 A large retrospective study of neurological diseases in cats using archived central nervous tissue identified inflammatory disease as the most common cause, mainly due to FIP. 7 This is in accordance with a retrospective study looking at the occurrence of spinal cord disease in cats identified on post-mortem examination and identified FIP, lymphoma, and neoplasia of the vertebral column secondarily affecting the spinal cord as the most common causes. 3 However, a more recent retrospective study investigating cats with clinical spinal disease where magnetic resonance imaging (MRI) was performed showed neoplastic disease to be the most common cause of spinal cord diseases. 8 Another report states that neoplasia is the second most common cause of extradural, extramedullary compression and often affects the vertebral body in cats. 9,10 Extradural lymphoma would be the most likely possibility in young animals and is often associated with feline leukemia virus, but it is still rare and often is characterized by bone lysis as opposed to new bone growth. 4,6,10 Osteosarcoma is the most common primary vertebral bone tumor in cats but is rare at a young age. 11 Diagnosis of spinal cord disease is made based on physical and neurological examination, clinical signs as well as spinal radiography, myelography, CT and MRI. 5 Cerebrospinal fluid analysis can be useful in determining if infection is present, but the results are often non-specific with non-infectious spinal cord disease. 2,5 In the cat in this report, where physical and laboratory examinations were inconclusive, diagnostic imaging was critical to the diagnosis of spinal cord compression.
Vertebral angiomatosis has also been reported with clinical and radiographic signs very similar to this patient in one case report. 12 Vertebral angiomatosis is considered a rare vascular malformation, characterized by the formation of multiple angiomas which are non-neoplastic tumors that form blood vessels. Histologically these lesions are benign proliferations of blood vessels of undetermined origin with well-differentiated vascular walls. 13
Three descriptions are available in the literature, describing the radiographic and histologic appearance of the disease in four cats 12,13 and the radiographic and CT finding in one cat. Each of the reported cats was between 1 and 2 years old, had a history of pain, paraparesis and ataxia. In all reported cases, the lesions were localized to the thoracic vertebral spine. Of the four previously reported cases, two underwent surgical decompression with no reported clinical signs a few months after surgery. Unfortunately, the cat in this case report died a few hours after surgery and necropsy was declined by the owners. However, the authors believe that the death was unrelated to the vertebral angiomatosis. To the author's knowledge, this is the second case report describing the CT findings in a cat with vertebral angiomatosis.
Other causes of new bone formation include bone abscess or infection, migrating foreign body, or congenital defect. 9,10
In young cats presented with back pain and paraparesis and new bone formation in the thoracic spine, the list of differential diagnoses should include benign but invasive diseases such as vertebral angiomatosis. Previously published reports describe a favorable prognosis after surgical management.