Abstract
A 15-month-old cat presented for evaluation of worsening generalized proprioceptive ataxia. Computed tomography of the cervical spine revealed the presence of a compressive extradural bony mass involving the dorsal aspect of C1. Surgical exploration and debulking of the mass was performed. Histological evaluation of the mass revealed fibrovascular tissue consistent with a vascular hamartoma. This mass was deemed to be originating from the soft tissue associated with the C1 vertebra with subsequent bony proliferation. Surgical debulking of the mass resulted in complete resolution of clinical signs with no evidence of recurrence 2 years after surgery.
A 15-month-old, 3.9 kg female spayed domestic shorthair cat was referred to the Iowa State University Veterinary Teaching Hospital (ISU-VTH) soft tissue surgery service for evaluation of a suspected nasopharyngeal polyp. The cat had been adopted 3 months prior to presentation from a local shelter. At the time of adoption, the cat had been fully vaccinated and tested negative for both feline leukemia virus and feline immunodeficiency virus. The cat first presented to the local veterinarian 1 month prior to referral for an owner complaint of a progressively worsening gait disturbance. The cat was started on a treatment protocol for suspected otitis media/interna. Despite therapy, the cat's abnormal gait continued to worsen and it was referred for further evaluation.
On presentation, the cat was quiet, but responsive and a general physical examination, including a fundic examination, was normal. On neurological evaluation, mentation, level of consciousness and cranial nerve examination were within normal limits. All four limbs were held in rigid extension and no postural reactions could be demonstrated. The cat had severe tetraparesis, equal in all limbs, and was unable to walk or stand without assistance. Spinal reflexes were normal. Palpation revealed significant pain of the cranial cervical spine. Based on these findings, the lesion was localized to the C1–C5 spinal cord segments. Differential diagnoses for a cat of this age with C1–C5 spinal cord signs include a developmental abnormality (subarachnoid cyst, syringomyelia, vertebral canal stenosis), infectious/inflammatory disease (feline infectious peritonitis, granuloma or focal myelitis), degenerative condition (lysosomal storage diseases, demyelinating diseases), or neoplasia.
The cat was transferred to the neurology service for further evaluation. A complete blood count and serum biochemistry were performed. The findings were unremarkable except for an increased serum alanine aminotransferase (ALT) (170 IU/l; reference range 20–125 IU/l), that was not pursued at this time due to owner's request. Urine collected by cystocentesis had a specific gravity of 1.010 (obtained post intravenous fluid support) with no other abnormalities noted. Thoracic radiographs were within normal limits.
The cat was anesthetized for computed tomography (CT) of the cervical spine, cerebrospinal fluid (CSF) collection and bilateral otoscopic examination (due to the history of previous otitis). The CT study of the cervical spine consisted of 2 mm contiguous axial acquisitions, pre- and post intravenous contrast (Omnipaque 240; GE Healthcare) administration. No mass lesions or areas of contrast enhancement were evident in the visible brain tissue and both tympanic bullae were air filled with thin, smooth walls. The images of the cranial cervical spine revealed substantial bone proliferation associated with the first cervical vertebra (C1). A second post-contrast series of 1 mm contiguous axial acquisitions was undertaken and revealed pronounced thickening of the right dorsal and lateral portions of the arch of the first cervical vertebra. The thickening measured 6 mm cranially, tapered to 2 mm caudally, compared to a 2–3 mm thickness on the left side. The outer border was well defined, the inner border was mildly irregular, and the intervening bone was less attenuating. The thickened bone reduced the spinal canal diameter by approximately 30%, compressing the spinal cord into the left ventral canal. No extraskeletal soft tissue changes were evident ( Fig 1 ). No significant contrast enhancement was noted. An otoscopic examination was normal. CSF was collected from the L5-6 subarachnoid space due to the structural abnormality noted at C1. Only a small amount could be obtained and cytological examination was consistent with peripheral blood contamination. The C1 compression was deemed to be the cause of the clinical signs. Differential diagnoses for this abnormality included neoplasia, proliferation resulting from a previous traumatic event, infection or a developmental abnormality. The cat was recovered from anesthesia so the owners could consider exploratory surgery in order to debulk the abnormal tissue and obtain a sample for histopathology.
Axial images of the thickened dorsal and right half of the arch of C1 at the level of the rostral end of the odontoid process. Both images are 1 mm slice thickness, the left depicted in a bone window, the right in a soft tissue window to demonstrate the compression of the spinal cord.
Three days later, a dorsal laminectomy at C1–C2 was performed using a standard approach. 1 The cranial portion of the C2 spinous process was removed using rongeurs, to gain better access to the caudal portion of the first cervical vertebrae. The right dorsolateral aspect of C1 was removed, using rongeurs and a high speed pneumatic drill, down to the level of the wing of C1. This bone was noted to be abnormal in arrangement and numerous pockets of soft, necrotic material were encountered. A compressive soft tissue mass, grey in color, measuring approximately 1 cm×1 cm, was encountered within the spinal canal following bone removal. During mass removal, considerable hemorrhage, followed by a decrease in systolic blood pressure was encountered. The hemorrhage appeared to be originating from the soft tissue mass itself, although a definitive source could not be identified. Packed red blood cell and fresh frozen plasma transfusions were administered, followed by a combined dopamine/dobutamine constant rate infusion (CRI) (10 μg/kg/min), a 15 ml bolus of 6% hetastarch and a 20 ml bolus of bovine hemoglobin (Oxyglobin Solution; Biopure). At this time, it was deemed unsafe to continue with additional removal of the mass. The surgical site was lavaged with sterile saline and closed routinely.
Following anesthetic recovery, the cat was placed in the intensive care unit (ICU) and continued to remain in critical condition for the next 5 days. During this time she was treated with 6% hetastarch in 0.9% sodium chloride solution intravenously, received one whole blood transfusion of 60 ml and was placed in an oxygen cage with a fraction of inspired oxygen (FiO2) of 40% in order to maintain a SpO2 above 98% (the first 2 days only). On day 2 postoperatively, she became more responsive and began to eat a canned critical care diet (a/d Canine/Feline Diet; Hill's Pet Nutrition) when offered. On day 5 postoperatively, her appetite increased and she began to drink water when offered. Intravenous fluid supplementation was discontinued. The following day, she was alert and responsive and showed signs of voluntary motor activity in all limbs. Due to financial concerns, the cat was discharged to her owners for continued care 8 days after surgery. At the time of discharge, she was weakly ambulatory in all limbs, bright, alert and her appetite continued to improve.
Four weeks postoperatively, the cat returned for a re-evaluation. Although tetraparetic, she displayed voluntary motor activity in all four limbs and was ambulatory without support. Postural reactions were normal. No pain was noted on head or spinal palpation and she appeared comfortable at home according to the owners. A follow-up examination was performed by the local veterinarian 2 years postoperatively. At that time, a complete physical and neurological examination revealed normal results.
Histopathology revealed the soft tissue mass was composed of numerous small arterioles and a few capillaries separated and surrounded by abundant pale basophilic extracellular matrix and fibrous tissue. There was no evidence of significant inflammation or invasive neoplasia ( Fig 2 ). The histopathological diagnosis was fibrovascular tissue consistent with a vascular hamartoma. The associated osseous tissue samples contained multiple pieces of trabecular bone, with some necrotic portions. These samples were bordered by fibrovascular tissue, which contained a few macrophages and lymphocytes. Other pieces of bone appeared to be proliferative and were bordered by fibrovascular tissue.
Numerous small arteriolar structures (black arrows) separated by basophilic extracellular matrix (M) (400× magnification photomicrograph, hematoxylin and eosin stain, bar=50 μm).
Vascular hamartomas are rare malformations of vascular tissue that are considered to be non-neoplastic and congenital. 2 In veterinary patients, vascular hamartomas have been described in many different organs or tissues including the lung, ovary, muscle, brain, spinal cord, subcutis, gingival mucosa, and liver. 3–13 This report describes a case of a vascular hamartoma arising from the cervical spine of a cat and to the authors' knowledge this is the first report of this rare malformation originating from this area in a feline.
Most clinical cases of vascular hamartomas are diagnosed early in life, before the onset of skeletal maturity, however, a delayed onset of signs has been reported.3,4,8,9 In this case report, the cat developed clinical signs of spinal cord compression within the first 16 months of life. This would be consistent with the continued development of a congenital lesion as is most commonly described in the literature. Previous medical history for this cat was unavailable, so the possibility of a previous trauma leading to a vascular overgrowth cannot be ruled out.
As hamartomas are considered to be histologically benign, the clinical signs most commonly associated with these anomalies are due to their space occupying or compressive nature and tendency to hemorrhage. 2–14 This space occupying and compressive nature was clearly demonstrated in this cat. Substantial spinal cord compression was seen with CT and was confirmed surgically. It was this compression that was subsequently deemed to be the cause of the patient's clinical signs.
In this case, removal of the hamartoma lead to excessive intra-operative hemorrhage which should be considered as a potential complication when attempting surgical removal of these lesions. In human spinal surgery, controlled hypotensive anesthesia is commonly used during procedures where considerable hemorrhage is expected. 15 In experienced hands, this could be a viable option to help reduce intra-operative blood loss and maintain essential visibility of the surgical field. Although the cat in this case survived the initial blood loss, significant morbidity was encountered and the extent of the blood loss made it unsafe to continue exploration of the area to ensure complete mass removal and surgical margins were poorly delineated. Fortunately, the possibility of significant regrowth is considered unlikely, as hamartomas contain well differentiated tissue and their growth is often finite.2,16 Follow-up imaging was not performed on this patient, but there has been no recurrence of clinical signs 2 years after surgical removal.
Although this diagnosis is expected to be rare, surgical removal can be considered a viable option for treatment of vascular hamartomas involving the spine.