6
Radiographic interpretation
• Stiffness, inactivity and/or reluctance to move
• Urine incontinence/scald
• Caecotroph accumulation
• Failure to groom, acariasis, myiasis
• Otitis externa (resulting from inability to groom the ears using the hindlimbs)
• Gastrointestinal stasis.
Positioning for radiography
Whole body survey radiographs are helpful to iden-tify concomitant underlying conditions, e.g. lung metastases or urolithiasis, that might otherwise go undetected. However, they should not replace tar-geted, well collimated radiographs of specific areas of interest localized by a thorough and systematic physical and neurological examination.
General anaesthesia is usually required to obtain accurate, diagnostic radiographs of the spine and is mandatory for myelography. Manual restraint and immobilization techniques may not provide the accu-rate positioning required for diagnosis, could cause artefacts and may result in further injury and stress to the patient (see Chapter 3 and Appendix 4).
Lateral view
For the lateral view it is essential that the spine is parallel to the cassette; the patient is placed in right or left lateral recumbency with the hindlimbs and forelimbs extended. Full extension should be main-tained only for the duration of exposure of the film, to avoid respiratory compromise. The limbs should be kept parallel to the cassette with the use of cotton wool or small foam wedges and should be secured to the X-ray table or cassette using tape; sandbags and rope ties are generally too bulky. For the cervical spine the skull should be positioned with the nares and pinnae in perfect vertical alignment; the nose may need to be ele-vated slightly with the use of a foam wedge. Foam supports may be positioned under the neck and lumbar spine to ensure that the spine does not kink, depending on the conformation of the rabbit.
Gentle traction on the skull and spine may be utilized with care to reduce rotation and other pos-itioning artefacts. Correctly positioned views should demonstrate superimposition of the osseous bullae, wings of the atlas, transverse processes, ribs and wings of the ilia (Figures 6.1 and 6.2).
(a,b) Normal lateral view of the cervical and thoracic spine of a 3-year-old entire male dwarf rabbit. Early signs of dental disease were an incidental finding. The alignment of the tympanic bullae (black asterisks), ribs (white squares), wings of atlas (red circles) and mandibles (yellow circles) denote correct positioning. (continues)
6.1
(a)
(b)
(continued) (c,d) ormal fle ed neck lateral view of the cervical and thoracic spine of a 3-year-old entire male dwarf rabbit. Early signs of dental disease were an incidental finding. The alignment of the tympanic bullae (black asterisks), ribs (white squares), wings of atlas (red circles) and mandibles (yellow circles) denote correct positioning.
6.1
(c)
(d)
(a) Normal lateral view of the lumbar spine of a 2-year-old neutered male Dwarf Lop rabbit presented with gastrointestinal stasis. (b) The alignment of the lumbar transverse processes (black circles), ribs (white squares) and wings of the ilia (red circles) denote correct positioning.
6.2
(a)
(b)
Ventrodorsal view
For the ventrodorsal (VD) view the patient is placed in dorsal recumbency, preferably supported by radio -lucent foam wedges or a plastic trough. The limbs may be held in a relaxed position or can be held with equal extension and slight inward rotation with the
use of adhesive tape fixed to the cassette or X-ray table. As before, gentle traction on the skull and spine may be utilized with care to reduce rotation and other positioning artefacts. Correctly positioned views should be symmetrical, with centrally posi-tioned spinous processes (Figure 6.3).
(a) Normal VD view of the lumbar spine of a 2-year-old neutered male Dwarf Lop rabbit presented with gastrointestinal stasis. (b) The symmetry and centrally positioned spinous processes (red circles) denote correct positioning.
6.3
(a) (b)
Myelography
Myelography is generally used to determine whether a bone or disc lesion identified on plain radiographs is causing spinal cord compression, or to identify spinal lesions not identifiable on plain radiographs such as neoplasia, abscesses and degenerative disc disease. The procedure for myelography is described in Technique 3.1.
As with other techniques, familiarity with normal myelographic anatomy is essential in order to interpret a myelogram effectively. The three main locations for pathological abnormalities that may be identified on a myelogram are intramedullary, intra-dural–extramedullary and extradural. Additionally, contrast medium may enter the spinal cord paren-chyma in cases of spinal cord malacia.
A number of significant side effects have been associated with myelography following injection of the contrast agent, including apnoea, seizures, hypotension and paresis/paralysis. In cats, keta-mine has been shown to raise intracranial pressure and increase the risk of brain herniation following withdrawal of cerebrospinal fluid (CSF). This may not be the case in rabbits, but it may be wise
to avoid ketamine in sedative/anaesthetic combina-tions during myelography in this species (Chitty, 2007). General anaesthesia is considered essen-tial, and intubation and intravenous access are recommended to reduce and/or treat potential complications that might occur.
A number of different techniques have been described in detail by Whittington and Bennett (2011) and Chitty (2007) and are described further in Chapter 3. Capello et al. (2008) commented that, anecdotally, injection of contrast medium into the cerebellomedullary cistern has resulted in the death of rabbit patients and suggested that there may be an apparent anatomical and/or physical contraindication to this procedure in this species.
However, other practitioners have successfully per-formed this procedure several times without com-plications (John Chitty, personal communication).
With more advanced imaging techniques such as computed tomography (CT) and magnetic reso-nance imaging (MRI) becoming more readily avail-able, myelography may become less useful or indeed desirable given the potential side effects associated with the procedure. However, myelo-graphy is readily achievable with minimal equip-ment, expense and experience and still has merit, especially in cases where speed of diagnosis is required, finances are limited, or the owner is unable to travel but still desires a more accurate diagnosis, e.g. cases of suspected spinal cord compression causing hindlimb paresis. In such circumstances a decision on prognosis and treat-ment may be made promptly with minimal stress to the patient, without the need for extra travel and an additional anaesthetic.
Approach to the paralysed or paretic rabbit
Generally a holistic medical approach to the rabbit patient is advised. Unfortunately poor rabbit
hus-andr is still c n is c pled it t e ra it’s tendency to hide illness, means that many rabbits presented to the veterinary surgeon will have more than one significant condition requiring attention, e.g. dental disease and degenerative joint disease, spinal disease and urine scald. Furthermore, the stress and/or pain of many conditions often mean that gastro intestinal stasis and/or ulceration are com-mon complications that need to be addressed if a successful outcome is to be expected.
The paralysed or paretic rabbit is typical of these cases. In the early stages of disease rabbits will have, or be at risk of, urine scald, gastro in test inal stasis and pododermatitis. With increasing severity and time, myiasis, urinary tract infections and pro-gression of pododermatitis to osteomye litis are increasingly common. Systemic diseases such as chronic renal failure, dental disease, malnu trition and hepatic lipidosis may be additional complications.
A suggested diagnostic approach to the para-lysed/paretic rabbit is summarized in Figure 6.4. It
Paralysis/paresis
Obtain complete history;
perform physical examination and neurological assessment
Localize lesion to one of four spinal cord segments or the
brain (see table below)
Brain/ear
Skull/bulla radiographs
CT/MRI Blood lead and serum E. cuniculi
antibody titres
Multifocal disease
Blood lead and serum Encephalitozoon cuniculi antibody titres; cerebrospinal
fluid analysis
Spine
Plain spinal radiographs
Cerebrospinal fluid analysis and
myelography or CT/MRI
Blood, urine or direct lesion culture if suspect discospondylitis
Assess haematology, serum biochemistry and urinalysis;
obtain survey thoracic and abdominal radiographs
Further investigation and treatment of any systemic
abnormalities identified
Brain Spinal cord division
Cranial cervical (C1–C5) Cervical enlargement (C6–T2) Thoracolumbar (T3–L3) Lumbosacral (L4–Cd) UMN signs in all four
limbs or fore- and hindlimb on single side; ± cranial nerve de cits altered ental state; seizures
UMN signs in both
forelimb(s) and hindlimb(s) LMN signs in thoracic limb(s);
UMN signs in pelvic limb(s);
reduced or absent ipsilateral c tane s tr nci re e i 1 segment involved
Normal thoracic limbs;
UMN signs in pelvic limb(s); reduced or absent c tane s tr nci re e caudal to the level of the last intact dermatome
Normal thoracic limbs;
LMN signs in pelvic limb(s); urinary incontinence; faecal incontinence
Suggested diagnostic approach to the paralysed/paretic rabbit. LMN = lower motor neuron signs; UMN = upper motor neuron signs.
6.4
is ideal to investigate the potential for underlying systemic diseases as thoroughly as possible.
Standard nursing protocols should include the provision of warm dry bedding with access to hay ad libitum. Great attention should be paid to the removal of oculonasal discharges and soiled/
matted fur. Administration of fluids, analgesics, prokinetics and antacids should be routine in most cases.
Normal radiographic anatomy
The vertebral formula of the rabbit is C7–T12–L7–
S4–Cd15–Cd16, although variations are relatively common. In a study by Greenaway et al. (2001) that evaluated 64 New Zealand White rabbits, 43.8% had 12 thoracic and 7 lumbar vertebrae, 32.8% had 13 thoracic and 6 lumbar vertebrae, and 23.4% had 13 thoracic and 7 lumbar vertebrae.
The lumbar vertebrae of rabbits have several differences from those of other domestic mammals.
The first three lumbar vertebrae have a ventral crest. All the lumbar vertebrae have a prominent mammillary process of the cranial articular process, where the powerful lumbar musculature attaches to the vertebral column. Unlike those of other domestic mammals, the dorsal aspect of the lumbar vertebral mammillary process is level with, or slightly ventral to, the spinous process. The first three vertebrae of the sacrum are fused, while the 4th sacral vertebra is fused variably.
Features that can be diagnosed using radiography
Vertebral deformities
Kyphosis (Figure 6.5), lordosis, scoliosis and hemivertebrae are common in pet rabbits. These deformities are often incidental findings but may also be associated with significant disease. Pain and/or reduced mobility secondary to these lesions may result in urine scald, perineal soiling with caeco -trophs and reduced ability to groom, which in turn increases the risk of myiasis and acariasis.
Kyphosis of the mid-thoracic spine in a 2-year-old neutered female Dwarf Lop rabbit with chronic perineal soiling. Reduced mobility resulting from the kyphosis resulted in caecotroph accumulation around the perineum. The problem was managed by regular shaving of the fur around the perineum, which reduced the accumulation of caecotrophs and allowed easier cleaning by the owner.
6.5
Deformities may be congenital but may also occur secondary to poor husbandry and diet. Diets that are low in calcium predispose the rabbit to reduced verte-bral bone density. Breeding does kept in small cages that restrict normal movement have been shown to have an increased prevalence of spinal deformity (Drescher and Loeffler, 1996); the increased demand for calcium due to gestation and lactation results in reduced vertebral bone density. Similarly, young growing rabbits fed on cereal mixes may develop nutritional secondary hyperparathyroidism, resulting in generalized demineralization of the skeleton.
Spondylosis
Spondylosis (Figure 6.6) is common in middle-aged and older rabbits and may occur anywhere along
Lumbar vertebral spondylosis in a Dwarf Lop rabbit with a history of reluctance to e ercise and obesity. There were no neurological deficits and there was no evidence of spinal pain. A calorie-controlled diet was advised, consisting of predominantly hay with an eggcupful of pellet diet daily. ree e ercise and foraging were encouraged.
6.6
the length of the spinal column. Clinical signs, if pre-sent, result from reduced flexibility of the spine and/or discomfort and are similar to those described for vertebral abnormalities.
Discospondylitis
In dogs, discospondylitis is thought to occur most commonly secondary to haematogenous spread of bacteria or fungi; sources of infection include migrating foreign bodies (grass awns), bacterial endocarditis, and dental and urinary tract infections (LeCouteur and Grandy, 2000). Given the apparent relatively high incidence of dental and urinary tract infections in rabbits, and their access to hay which often contains awns, it is perhaps surprising that discospondylitis appears to be rare in rabbits. This may simply reflect under-diagnosis, again due to the ra it’s tendenc t as pain and t e di ic lt in obtaining a definitive diagnosis of the condition.
In dogs, typical radiographic signs are destruc-tion of the bone endplates adjacent to an infected disc, collapse of the intervertebral disc and varying degrees of new bone formation; similar signs would be expected in affected rabbits (Figure 6.7).
Supporting evidence for discospondylitis may include increases in CSF white cell counts and protein levels, and/or positive urine, blood or
Discospondylitis in a 7-year-old neutered male rabbit with a recent history of sudden-onset severe depression lethargy and anore ia. hysical e amination revealed hindlimb paresis lumbar pain and a doughy abdomen. Abnormalities on the radiograph include collapse of the intervertebral disc spaces and osteosclerosis of the vertebral endplates from T T through to . alcified disc material is visible in the
intervertebral foramen. There is also gas dilation of the gastrointestinal tract. The owner declined further investigation and elected for euthanasia.
6.7
CSF cultures. The use of CT/MRI and surgical explor ation to obtain samples for culture and cyto-logy may be required in selected cases to obtain a definitive diagnosis.
Intervertebral disc disease
In the laboratory rabbit, intervertebral disc disease (IVDD) would appear to be relatively common;
Green et al. (1984) performed post-mortem exam-inations of the spines of 35 laboratory rabbits rang-ing in age from 3 months to 8.5 years. They observed degenerative changes of the intervertebral disc (IVD) in individuals as young as 3 months and vertebral spondylosis in animals from 24 months of age, which suggests that at least subclinical disc disease may occur frequently in pet rabbits.
Clinical reports of IVDD are rare in the rabbit, though this may reflect under-diagnosis. Smith Baxter (1975) described two cases of disc pro-trusion and expro-trusion of nuclear material in pet rabbits, associated with posterior paralysis and urinary and faecal incontinence. Both cases ap-peared to result from hyperflexion of the spine and resulted in compression of the spinal cord. Both rabbits were euthanased after failing to respond to corticosteroids.
Clinically, IVDD may be demonstrated by radio-pacity of the intervertebral disc space (IVDS) with or without the presence of mineral opacities in the intervertebral foramen and/or narrowing of the IVDS (see Figure 6.7). Spinal cord compression may be confirmed by myelography (Figure 6.8), CT or MRI.
ateral myelographic view of an e tradural compression on the ventral aspect of the spinal cord at the intervertebral disc interspace of a rabbit that had sustained a fracture of the vertebral endplate of the th lumbar vertebra. ourtesy of rances Harcourt Brown)
6.8
Forelimb neuropathy
Forelimb neuropathy in a rabbit was attributed to lat-eralized intervertebral disc protrusion (John Chitty, personal communication). The affected individual presented with an abducted forelimb and triceps muscle wastage associated with spondylitic lesions at T1–T2 and T3–T4 (Figure 6.9).
Muscle wastage and cutaneous sensitivity can be used to localize the lesion. It appears that the order of nerve emergence from the brachial and
Radiograph of a 6-year-old giant-breed rabbit presenting with the right forelimb e tended laterally at a degree angle from the body. astage of the triceps musculature was noted; the left forelimb was also affected but to a much lesser e tent. There is spondylosis evident at T T and T T . ohn hitty
6.9
lumbosacral plexuses and the muscles innervated are similar to those in dogs. Survey spinal radio-graphs in such cases may demonstrate IVDD, enlarged intervertebral foramina in cases of periph-eral nerve sheath tumours, or lytic changes indica-tive of other neoplasms or infection.
Fractures and luxations
The most common site of vertebral fracture or luxa-tion is in the lumbosacral region (L6–L7). Injuries are most frequently caused by improper restraint (Figure 6.10). In some cases the injury may occur when a rabbit is not being handled but is attempting to flee a perceived or actual danger. Such cases may be presented having been found by the owner with acute hindlimb paresis or paralysis with no history of trauma or handling.
Sublu ation of the rd lumbar vertebra in a year old crossbreed neutered female rabbit with a history of hindlimb paresis following a recent fall from its hutch. The clinical signs improved following treatment with oral melo icam.
6.10
Spinal injuries resulting from dog (Figure 6.11) or fox bites, falls and entrapment under furniture, and/or being trodden on by owners, are also rela-tively common in pet rabbits, whilst gunshot in-juries and road traffic collisions are common in wild or stray rabbits.
Injuries are usually readily identified on plain sur-vey radiographs but some cases are subtle, and myelography or more advanced imaging such as CT/MRI may be required to identify lesions and, more importantly, to assess spinal cord trauma.
Luxation may be transient following a traumatic event and radiographic signs may be subtle despite significant injury and spinal cord trauma.
Excess mineralization
Chronic renal failure in rabbits can lead to hyper-calcaemia as a result of impaired excretion of cal-cium by the kidney in the face of continued calcal-cium absorption from the intestine (Harcourt-Brown, 2007). Excess calcium may subsequently be depos-ited in the skeleton (osteosclerosis) and soft tissue, resulting in excess mineralization of these structures which is readily appreciable on radiographs (Figure 6.12). Nephroliths and aortic calcification may be identifiable on survey spinal radiographs. This is in contrast to dogs and cats, in which chronic renal failure is more likely to cause mineral loss from the axial skeleton as a result of renal secondary hyperparathyroidism. Hyper vitaminosis D may cause identi -cal lesions.
Owing to the generalized nature of the skeletal changes, and particularly in the early stages of disease, excess mineralization is easily overlooked.
Reference to a normal rabbit radiograph is invalu-able for comparison and, ideally, a prepared bone or bones may be placed alongside the patient during radiography for comparison. This helps to minimize the effect of inadequate exposure and/or faults in developing the film.
Neoplasia
Primary neoplasia of the spinal column appears to be rare; however, with the increasing age of the pet rabbit population and owners seeking more pro active veterinary investigations and treatment, it would seem likely that more cases of spinal neoplasia will be reported in the future. Published cases include osteosarcoma (Weiss and Müller, 2011) and lym-phoma (Reed et al., 2009). Metastatic neoplasia is possible and is most likely to be associated with uter-ine adenocarcinoma.
References and further reading
Capello V, Lennox AM and Widmer WR (2008) The basics of radiology (contrast radiography). In: Clinical Radiology of Exotic Companion Mammals, ed. WR Widmer, pp. 40–42. Wiley-Blackwell, Ames, IA Chitty J (2007) Clinical techniques: the subarachnoid space, its clinical
relevance in rabbits. Journal of Exotic Pet Medicine 16, 179–182 resc er and e er 1 c li sis l rd sis and p sis in
breeding rabbits. Tierärztliche Praxis 24, 292–300
Green PW, Fox RR and Sokoloff L (1984) Spontaneous degenerative spinal disease in the laboratory rabbit. Journal of Orthopaedic Research 2, 161–168
Greenaway J, Partlow G, Gonsholt N et al. (2001) Anatomy of the lumbosacral spinal cord in rabbits. Journal of the American Animal Hospital Association 37, 27–34
Harcourt-Brown FM (2007) Radiographic signs of renal disease in rabbits. Veterinary Record 160, 787–794
LeCouteur RA and Grandy JL (2000) Diseases of the spinal cord. In:
Textbook of Veterinary Internal Medicine, 5th edn, ed. SJ Ettinger, pp. 608–656. WB Saunders, Philadelphia
Reed SD, Shaw S and Evans DE (2009) Spinal lymphoma and p l nar lariasis in a pet d estic ra it Oryctolagus cuniculus domesticus). Journal of Veterinary Diagnostic Investigation 21, 253–256
Smith Baxter J (1975) Posterior paralysis in the rabbit. Journal of Small Animal Practice 16, 267–271
Weiss ATA and Müller K (2011) Spinal osteolytic osteosarcoma in a pet rabbit. Veterinary Record 168, 266
Whittington JK and Bennett RA (2011) Clinical technique: myelography in rabbits. Journal of Exotic Pet Medicine 20, 217–221
ertebral body fracture in a year old entire female Dutch rabbit with a recent history of dog attack. The rabbit presented with acute onset hindlimb paralysis with no deep pain sensation. The rabbit was euthanased.
6.11
arked generali ed osteosclerosis of the a ial and appendicular skeleton of a 6-year-old entire male Dwarf op rabbit with chronic renal failure. The rabbit was presented because of forelimb pain and polydipsia. ote also the calcified aorta which is a common feature in chronic renal failure.
6.12