DISC HERNIA

The intervertebral discs (IVDs) are fibrocartilage structures interposed between the vertebrae that act as shock absorbers by resisting the compressive forces to which the spine is subjected and which allow the latter to move.

The intervertebral disc is structurally distinguishable in an innermost part, represented by the pulpy nucleus, very hydrated and gelatinous, and an outer part, containing, the fibrous ring.

Degenerative phenomena affecting IVD are responsible for a pathology frequently encountered in dogs: the herniated disc, classified, in 1950, by Hansen, in type I and type II disc herniation and, recently, the new techniques of MRI identified another form of disc herniation, acute high velocity low volume disc disease (HVLV - high velocity low volume) also called Hansen 3 disc herniation; this classification is attributable to the type of degenerative phenomenon that causes the herniation.

In Hansen's hernia type 1 the nucleus pulpus is gradually replaced by hyaline cartilage (chondroid degeneration), the fibrous ring weakens until it cracks or breaks, allowing the nucleus pulposus to "extrude" in the dorsal or dorso-lateral direction with consequent compression of the spinal cord. This form of hernia is typical, although not exclusive, of the so-called “chondrodystrophic” breeds (dachshund, beagle, Pekingese, Shih Tzu) and has an acute onset.

Type II Hansen's hernia, on the other hand, is characterised by a fibroid degeneration of the pulpus nucleus which causes mostly partial fissures of the annulus, which usually remains intact in its outermost layers. In this situation, a disc protrusion is generated whose onset is slower than the previous one. This type of hernia has no predilection for breeds and occurs mainly in elderly subjects.

The clinical response varies according to the tract of the vertebral column concerned and is, in any case, dominated by pain whose etiopathogenetic mechanisms are many: medullary, radicular and vascular compression; inflammation of neighbouring structures; stimulation of disc nociceptors; muscle contractions; meningeal reaction with formation of adhesions.

A cervical disc herniation will manifest itself with intense pain in the neck, stiffness, lowered head, kyphosis, spontaneous yelping and the involvement of the cervical-thoracic tract will also cause pain in the forelimb and lameness. In severe cases, cervical disc disease can lead to paresis or paralysis.

When the thoraco-lumbar portion is affected by this pathology, which occurs more frequently, the dog will present back pain, arching of the spine (kyphosis), tremors, reluctance to move up to paraparesis, hyper-reflexia , weakness, paralysis - pain sensitivity is lost in this stage. Moreover, during the neurological examination, an increase in skin sensitivity in the area of ​​the lesion and a hyposensitivity downstream of it will be noted. Urinary incontinence with small-jet urination is also typical, called a "spastic bladder".

Mixed incontinence, on the other hand, is indicative of the involvement of the lumbo-sacral tract which will have lameness in the hind limbs, paraparesis, paraplegia, reduction or absence of reflexes as other manifestations.

Obviously these pictures can be combined in various ways in case of multifocal lesions.

The diagnostic suspicion is raised by the symptoms and the neurological examination, but must be confirmed by imaging methods, the most specific of which is Magnetic Resonance, which allows the location and extent of the hernia to be correctly identified.

Depending on the severity (five progressive severity classes have been identified), we will intervene with conservative treatment (absolute immobility, painkillers, specific diet plan to reduce the weight of the animal and then gradual resumption of motor activity) or, in the most severe and in the forms of cervical discopathy, surgical intervention will be resorted to.

The surgical technique adopted for thoraco-lumbar tract hernias is hemilaminectomy which "releases" the compressed spinal cord with the removal of the right or left lamina of the vertebral roof and with the subsequent removal of the portion of the herniated disc (today it is possible to use minimally invasive techniques of "mini-hemilaminectomy").

For the cervical region, on the other hand, the ventral slot is preferred, in which herniated disc material is removed with a ventral access to the column created in correspondence with the intervertebral disc concerned. 

Depending on the severity of the pre-operative clinical picture, the timeliness of treatment and the type of spinal cord damage that has occurred, recovery may be total, partial or, sometimes, unfortunately, absent: usually normal motor activity is reacquired over a period of time ranging from two to ten weeks.