INTRAOPERATIVE SPINAL ULTRASONOGRAPHY IN TWO DOGS WITH SPINAL DISEASE

Ultrasonography was performed during spinal surgery on two dogs that were suspected of having intramedullary lesions by myelography and magnetic resonance imaging. Ultrasonographically, the pathologic conditions of the spinal canal or cord were adequately imaged during surgery in both dogs. On the basis of ultrasonographic findings, a biopsy was obtained in Patient 1 and removal of the lesion was accomplished in Patient 2. Histopathologic diagnosis was myelomalacia in Patient 1 and spinal nephroblastoma in Patient 2. Intraoperative ultrasonography was demonstrated to be suitable for detecting intradural conditions, and, thus, is valuable for increasing the accuracy of biopsies or completeness of resections of intramedullary lesions.     

SPINAL SUBARACHNOID CYST IN A CAT

A 7-year-old neutered female domestic short hair cat was presented with hind limb ataxia. A subarachnoid cyst in the T10-T11 spinal cord region was identified by myelography as a collection of contrast medium in the subarachnoid space.     

ULTRASONOGRAPHIC ANATOMY OF THE NORMAL CANINE SPINAL CORD AND CORRELATION WITH HISTOPATHOLOGY AFTER INDUCED SPINAL CORD TRAUMA

Prior to trauma, intraoperative ultrasound of the spinal canal in 31 normal dogs was performed through a hemilaminectomy in the left pedicle of L2. A ventral compressive model of spinal cord injury was performed as part of a clinical drug trial. Maximum ultrasonographic spinal cord diameter ranged from 4.9–7.2 mm (5.7 × 0.6). Significant positive correlation (p = 0.023, r = 0.49) was found between age and spinal cord diameter. The dura mater was a separate, well-defined, echogenic horizontal line in 28 (90%) dogs, dorsally, and in 29 (94%) dogs, ventrally. Cerebrospinal fluid was anechoic. Eighteen (58%) dogs had a well-defined anechoic dorsal subarachnoid space, whereas 22 (71%) had a well-defined ventral space. Pia mater was thin but strongly echogenic and covered spinal cord. Central canal was a double hyperechoic line in 17 (55%) dogs and a single-line in 14 (45%) dogs. A difference in the ultrasonographic appearance between gray and white matter was not seen. Epidural fat and connective tissue was a lobular echogenic material in the ventral epidural space. The periosteal-vertebral body interface was seen as a bright curvilinear echo with distal acoustic shadowing. Spinal cord parenchyma could be classified subjectively into four groups based upon ultrasonographic appearance. Spinal cord parenchyma had a uniform hypoechogenicity in 8 (27%) dogs (Group 1), subtle low level echoes in 7 (23%) dogs (Group 2), multiple clusters of defined echogenic foci in 12 (37%) dogs (Group 3), and multiple sharply-defined linear echoes in 4 (13%) dogs (Group 4). There was a significant relationship between pre-trauma ultrasonographic appearance of the spinal cord and histopathology 21 days after trauma. One (13%) dog in Group 1, 4 (57%) dogs in Group 2,10 (91%) dogs in Group 3, and 3 (75%) dogs in Group 4 had malacia on histological evaluation. Therefore, dogs with echogenic spinal cords or linear echoes within cord parenchyma were significantly more likely to develop malacia rather than Wallerian degeneration after induced spinal cord trauma (p = 0.002). Spinal cord echogenicity may indicate vascularity in a segment of spinal cord and might be prognostic following spinal cord trauma. No complications were found related to intraoperative ultrasound. Hematoma or fibrous tissue formation appeared to impede percutaneous ultrasound of the spinal cord in dogs re-evaluated forty-eight hours and one week after surgery.     

SPINAL SUB ARACHNOID CYSTS IN 13 DOGS

Thirteen dogs, including 6 Rottweiler dogs, exhibiting clinical signs of spinal cord dysfunction and myelographically confirmed subarachnoid space enlargement were investigated. To characterize the lesions and to get a better understanding of their pathogenesis, different imaging techniques were used in association with explorative surgical procedures (12 dogs) and histopathologic techniques (5 dogs). All subjects underwent preoperative myelography, five of which were examined by computed tomography (CT) scanning and one by magnetic resonance imaging (MRI) as well as cerebrospinal fluid (CSF) flow measurement (velocimetry). Most animals were <12 months old (7/13 dogs) and Rottweilers were over-represented (6/13 dogs). The lesions were mainly located dorsally with respect to the spinal cord (10/13 dogs) and in the cranial cervical area (8/13 dogs). MRI suggested spinal cord deviation with signs of ventral leptomeningeal adhesion opposite the enlarged space. In one dog, velocimetry confirmed that the "cyst" was freely communicating with the surrounding CSF space. Surgical investigation confirmed leptomeninges-induced ventral adhesion in 4/5 dogs. Follow-up studies, carried out from 6 months to 2.5 years postoperatively, showed there was full recovery in 8/13 dogs. This study suggests that the compression of the spinal cord is possibly not caused by a cyst. Adhesion resulting from a combination of microtrauma and chronic inflammatory processes induces a secondary enlargement of the subarachnoid space and may be a significant causative factor in spinal cord compression and dysfunction. The over-representation of Rottweilers and the young age of the animals in the study suggest a possible genetic predisposition and an inherited etiology.     

IMAGING OF A SPINAL NEPHROBLASTOMA IN A DOG

An 8-month-old German Shepherd dog was presented for investigation of pelvic limb gait abnormality. Neurolocalization indicated a T3-L3 spinal cord lesion. The myelographic appearance was of an intramedullary lesion at T9/10, but upon subsequent magnetic resonance imaging it was determined that the mass was extramedullary. A diagnosis of nephroblastoma was made on histological examination. The imaging features of this rare tumor and the differentiation of intradural-extramedullary and intramedullary masses are discussed.     

THE USE OF HYPOTHERMIA IN SPINAL CORD DECOMPRESSION

In 1970 and in 1972 we reported on the use of local hypothermia as an aid in spinal surgery of the dog (Lumb and Brasmer, J.A.V.M.A., Aug. 1, 1970 and Brasmer and Lumb, Am. J. Vet. Res., March, 1972). These reports developed from a purely research project which involved extensive manipulation of the lumbar spinal cord. Preliminary studies had led us to expect a long period of postoperative paraparesis or paraplegia. We were aware of the work of Negin, Albin, White and others which indicated that hypothermia, both general and local, reduced the sensitivity of the spinal cord to trauma. In fact, their work strongly indicated that cooling even after trauma was highly desirable.     

USE OF INTRAOPERATIVE ULTRASONOGRAPHY IN CANINE SPINAL CORD LESIONS

The purpose of this retrospective study was to describe the intraoperative appearance of various spinal cord conditions, and to investigate how intraoperative ultrasonography assisted in modification of surgical and postoperative treatment plans. Intraoperative ultrasonography (B-mode, and power Doppler mode) was used in 25 dogs undergoing spinal surgery. The neurologic conditions included cervical spondylomyelopathy, intervertebral disc (IVD) protrusion, IVD extrusion, spinal tumors, nerve sheath mass, granulomatous myelitis, and discospondylitis. All of these diagnoses were supported by histopathologic and/or cytologic evaluation. It was possible to visualize the spinal cord and the abnormal spinal tissue in all of the patients. Power Doppler imaging allowed assessment of the spinal cord microcirculation, and assisted in judgment of the degree of decompression. Ultrasound imaging directly impacted the surgical and the medical treatment plans in four patients. Owing to the intraoperative imaging, two hemilaminectomies were extended cranially and caudally, and additional disc spaces were fenestrated, one hemilaminectomy site was extended dorsally to retrieve the disc material from the opposite side, and one intramedullary cervical spinal cord lesion was discovered, aspirated, and consequently diagnosed as granulomatous inflammation, which altered the long-term medication protocol in that dog. This study suggests that intraoperative sonographic spinal cord imaging is a useful and viable technique.     

MAGNETIC RESONANCE IMAGING FEATURES OF CERVICAL SPINAL CORD MENINGIOMAS

The records of four dogs with cervical spinal cord meningiomas were retrospectively reviewed. Signalment, history, laboratory findings, neurological examination, and histopathological findings were evaluated. Magnetic resonance imaging (MRI) was performed using a 1.0-T superconducting magnet and T2-weighted (W) and noncontrast and postcontrast T1-W spin echo pulse sequences. Meningiomas were located at the level of the second, third, and fifth cervical vertebrae and the C2-3 intervertebral space. All meningiomas appeared as focal masses that were hyperintense to the spinal cord on T2-W images and iso- to hypointense on the T1-W images. They could be identified as intradural and extramedullary in origin based on a broad-based dural margin seen on at least one of the imaging planes and a gradual expansion of the subarachnoid space cranial and caudal to the mass, best noted on the transverse and dorsal plane images. On dorsal plane T2-W images in three dogs, expansion of the subarachnoid space adjacent to the mass appeared similar to the myelographic "golf tee" sign. All meningiomas exhibited moderate, well-defined contrast enhancement with dural tails seen in three of the four dogs. One dog had extension into the intervertebral foramen along the nerve and ipsilateral atrophy of the muscles of the neck. By differentiating the meningiomas from intramedullary tumors and by clearly depicting the extent of the masses, MRI provided valuable information about treatment options and prognosis.     

POSTOPERATIVE IRRADIATION OF SPINAL CORD TUMORS IN 9 DOGS

Between 1985 and 1993, nine dogs with spinal cord tumors were treated postoperatively with cobaltradiation at North Carolina State University-Veterinary Teaching Hospital. Total doses ranged between 33.3–48.0 Gy given in 10–12 fractions of 3–4 Gy over a four week period. Five dogs were euthanized due to recurrence of the tumor or neurologic signs and two dogs were euthanized due tounrelated problems. Two dogs were alive but lost to follow-up at 12 and 25 months. Survival time ranged from 6.5–70.0 months. Median survival time (95% confidence interval) was 17 (12–70) months. Results of this study suggest decompressive surgery followed by irradiation can be an effective treatment for dogs with spinal cord tumors.     

IMAGING DIAGNOSIS—SPINAL CORD HEMANGIOMA IN TWO DOGS

Intramedullary masses are a dilemma due to the limited access for a nonsurgical biopsy, thus, accurate imaging characterization is crucial. Magnetic resonance imaging findings of two confirmed canine thoracic intramedullary hemangiomas are described. A capillary hemangioma was of mixed intensity but predominantly T2‐hyperintense and mildly T1‐hyperintense to spinal cord with strong contrast enhancement. A cavernous hemangioma had a target‐like appearance in both T1‐weighted (T1w) and T2‐weighted (T2w) images. In T2w images there was a small isointense center surrounded by a relatively large hyperintense area. In T1w images, there was a large isointense centre with a relatively small hyperintense periphery. Such characteristics should prioritize hemangioma as a consideration in a progressive myelopathy due to an intramedullary mass.     

IMAGING DIAGNOSIS—SPINAL EPIDURAL HEMANGIOSARCOMA IN A DOG

An 8‐year‐old, male Boxer was examined for an acute onset of ambulatory paraparesis. Neurologic examination was consistent with a T3‐L3 myelopathy. Myelography revealed an extradural spinal cord compression in the region of the T10‐T13 vertebrae. On magnetic resonance (MR) imaging, a well‐defined epidural mass lesion was detected. The mass was mildly hyperintense on T1‐weighted, hyperintense on T2‐weighted and STIR images compared to normal spinal cord and enhanced strongly and homogenously. Postmortem examination confirmed a primary epidural hemangiosarcoma. Findings indicated that the MRI characteristics of spinal epidural hemangiosarcoma may mimic other lesions including meningioma and epidural hemorrhages/hematomas of non‐neoplastic etiology.