Carcinoid in the lung of a hooded seal (Cystophora cristata)

The dog was regularly re-examined during the six months after surgery. Its condition improved both clinically and neurologically, and it lived a normal, active life from about four months after surgery. The differential diagnoses of a T3-L3 lesion with acute onset should include thoracolumbar disc herniation, fibrocartilaginous embolism (FCE), trauma, neoplasia, haemorrhage, and inflammatory diseases such as discospondylitis or meningomyelitis. Analysis of the CSF in this case showed a non-specific elevation of the protein level, judged to be a result of blood-brain barrier leakage, which could be the result of any one of the differential diagnoses. Survey radiographs did not indicate primary bone neoplasia, discospondylitis or skeletal trauma as the cause of the neurological signs. The myelographic finding of an extradural space-occupying lesion excluded FCE and meningitis/myelitis. Although soft tissue neoplasia might have this appearance, this was considered less likely because of the history and the location of the lesion over the T3-T4 disc space. The tentative diagnosis was a chronic disc prolapse. Additional traumatic injuries of the soft tissues ventrally in the vertebral canal at the site of the prolapse could not be excluded. Secondary soft tissue changes, consisting of inflammatory reactions, haemorrhage and thickening of the ligamentous structures, could have further amplified the mass effect of the extradural lesion. Trauma was considered to have been a factor in this case. The traumatic episode one week before the onset of clinical signs was thought likely to have been the initiating event, although the trauma per se did not cause any neurological signs. When the dog slipped and fell, cranial, caudal or adducting forces to the involved ribs might have created a traumatic overextension and tearing ofthe topical intercapital ligament, thus predisposing degenerated disc material to herniate into the vertebral canal through the weakened intercapital ligament at a later time. Histopathology of the tissue fragment indicated a fragmentation of the annulus fibrosus and the vertebral epiphysis. It is reasonable to assume that this was induced by the initial trauma. However, no fragmentation of the vertebral epiphysis was seen on plain radiographs, nor was the aberrant fragment of the annulus fibrosus detected by myelography. This could be due to the small size of the tissue fragment, in conjunction with overlapping anatomical structures, which would have obscured the object. Given the delay of about one month between myelography and surgery, the fragmentation might have occurred later in the course of the disease, but the presurgical clinical history contradicted this possibility. The myelographic finding of an extradural lesion at the T3-T4 disc space, in conjunction with the surgical finding of disc material dorsolaterally on the dura mater, and the dog's neurological history before and after surgery, strongly indicated a T3-T4 disc herniation. The occurrence of a disc prolapse at this site was probably preceded by an injury to the intercapital ligament; the external trauma from a violent fall one week before the onset of neurological signs is suspected to have caused this injury. This conclusion was drawn without the disc having been inspected in situ, since the spinal cord covering the disc is a vulnerable tissue and care was taken not to displace the spinal cord during the dorsal laminectomy. This is, to the authors' knowledge, the first reported case of a disc prolapse in the cranial thoracic spinal region of a dog.