Andy Shores1 and Allison Mooney2 1 Mississippi State, MS, USA 2 Boise, ID, USA Patients with cervical IVD protrusions often present with a history of sudden crying out in pain, neck guarding, and muscle fasciculations about the head and neck. The signs may occur spontaneously or in response to exercise or may be apparent when the animal is petted about the head. The history may include a decrease in activity, since any sudden movement elicits excruciating pain, or it may indicate intermittent episodes with varying degrees of pain. Others are presented with variable signs of severe tetraparesis, either ambulatory or non‐ambulatory, from an acute disk extrusion [1]. Cervical IVD protrusion is most common in the chondrodystrophic breeds. Non‐chondrodystrophic breeds can also be affected with the cervical vertebral instability (“wobbler”) syndrome appear to have a higher incidence of cervical IVD protrusions than other non‐chondrodystrophic breeds (Figure 5.1). Figure 5.1 Sagittal and transverse CT images of an IVD extrusion that produced acute, severe tetraparesis in a 6‐year‐old male Doberman Pinscher. The clinical signs of cervical IVD protrusion are related to the dynamic force of compression and the mechanical displacement of the spinal cord and cervical nerve roots by the extruded disk material. The signs can include hyperesthesia of the neck and forelimbs, painful spasms of the neck muscles, ataxia, or tetraparesis. Most cervical IVD protrusions, even when massive, are manifested by pain only (Figure 5.2). Pain is the hallmark of cervical IVD protrusion and may be constant or intermittent. Most of the pain is of radicular (nerve root) origin; some may be associated with meningeal initiation or “diskogenic” pain [1, 2]. Figure 5.2 A Beagle presented for severe, persistent neck pain that was exhibited at any time the dog tried to move. Diagnostics revealed a C3–C4 IVD extrusion in this chondrodystrophic dog. Neurologic deficits are usually mild when present in cervical IVD disease (e.g., reflex alterations, proprioceptive deficits) and are often associated with progression of the disease. The acute type I protrusion can produce sudden and severe neurologic deficits (e.g., ambulatory or non‐ambulatory tetraparesis), can appear clinically indistinguishable from meningitis, or can be manifested by pain only. The type II protrusion has a much slower onset but may have very similar clinical signs with progression of the protrusion [3, 4]. The radiographic signs of cervical IVD protrusion are narrowing of the IVD space, narrowing of the intervertebral foramen, increased density (“cloudiness”) in the intervertebral foramen, and the presence of a mineralized mass within the spinal canal above the IVD space (Figure 5.3). One or more of these signs may be present. Clinically, the C2–C3 and C3–C4 intervertebral disks have the highest incidence of protrusion. Figure 5.3 A lateral radiograph demonstrating narrowing of the IVD space at C4–C5, narrowing of the intervertebral foramen, increased density (“cloudiness”) in the intervertebral foramen. Myelography is also helpful in delineating the lesion (Figure 5.4). Often, for suspected cervical IVD disease, a non‐ionic contrast material approved for intrathecal use is injected into the sub‐arachnoid space of the anesthetized patient and is used to outline deviation in the spinal cord that would indicate an extramedullary/extradural mass (compression). Myelography is easy to perform and generally carries a minimal risk; however, it is not as detailed as cross‐sectional imaging techniques (magnetic resonance imaging – MRI; computed tomography – CT). Figure 5.4 A lateral view of a myelogram study demonstrating an extramedullary/extradural mass effect over the C6–C7 IVD space, later confirmed at surgery to be an IVD extrusion. CT is often performed in sedated patients and in chondrodystrophic dogs often provides a diagnosis without the use of contrast as these disks often contain a high mineral content (Figure 5.5). At other times, especially in non‐chondrodystrophic patients, CT is combined with myelography in the anesthetized patient to provide a very definitive diagnosis of spinal cord compression (Figure 5.6). Figure 5.5 CT images of an IVD extrusion at C5–C6 in a chondrodystrophic dog. (a) Reconstructed sagittal view; (b) transverse bone window; (c) transverse soft‐tissue window. The patient only required sedation for these images and did not require contrast administration for this diagnosis. Figure 5.6 A CT‐myelogram transverse view demonstrating an IVD extrusion causing severe compression of the cervical spinal cord. MRI is very useful in the diagnosis of IVD disease (Figure 5.6). Its high level of tissue contrast often gives the neurosurgeon a very definitive view of the herniated material in the spinal canal; however, because of its sensitivity, some subtle or non‐clinical lesions may also be identified – hence the need for a very through clinical examination and localization of the offending lesion. Surgical management of cervical IVD syndrome is often warranted. Mild pain and muscle spasms can be amenable to conservative therapy. The merits of medical versus surgical therapy and the incidence of recurrence should be discussed with the owner; however, advanced imaging early in the course of the disease may dictate earlier surgical intervention with CT or MRI findings of an especially large extrusion that is unlikely to respond to medical management long term (Figure 5.3). Proper medical management may be of particular importance when there are financial considerations. Surgical candidates should be carefully evaluated through examination procedures and presurgical laboratory profiles and thoracic radiographs in patients over 5 years of age or with cardiac disease. Thorough knowledge of the anatomy and surgical approaches to the cervical vertebrae is essential in performing the described procedures (Figure 5.7). The indications for surgical management of cervical IVD syndrome are persistent pain, muscle spasms, or paresis, and certainly after prolonged failed conservative therapy and marked neurologic deficits (proprioceptive deficits, ataxia, tetraparesis); and pain with imaging showing evidence of extruded disk material in the cervical spinal canal. Surgical management consists of decompression of the cervical spinal cord. Fenestration of other cervical disks (C2–C3 through C5–C6) is often performed as a prophylactic procedure in chondrodystrophic dogs. Decompression is performed to remove IVD material from the spinal canal and to relieve pressure on the spinal cord [1]. Figure 5.7 Sagittal and transverse T2‐weighted MRI sequences of a C6–C7 IVD compression of the cervical spinal cord at that site.
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Cervical Ventral Slot Decompression
Cervical IVD Syndrome
History
Clinical Signs
Radiographic Signs
Advanced Imaging
Indications for Surgery
Ventral Approach to the Cervical Spine
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