Sacrococcygeal injuries in the cat, by Jean Louis Trouillet. ECVS, DESV chirurgie, Jan.24.2010

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Tail traumas in the cat lead to sacrum or vertebral tail fractures or to luxation between sacrum and tail vertebrae. These lesions are often associated with neurologic dysfunction of micturition and defecation which is not function of the localisation of the lesion. This dysfunction is associated with lesion of the sacral segments, of the cauda equina or of the nerves.

Anatomy

Nervous roots of sacrococcygeal canal give rise to the pelvic, pudendal and coccygeal nerves.
Cellular bodies of pelvic and pudendal nerves are in the sacral segments between the 5° and 6° lumbar vertebra. Cellular bodies of coccygeal nerves are between the 6° and 7° lumbar vertebra.
Lesions can reach nerves, cauda equina, sacral segments.

Functions of pelvic, pudendal, coccygeal nerves

• Pelvic nerve is a nerve of the parasympathic system; it is made of nervous roots of the 2° and 3° sacral segments (+ 1° sacral segment in many cats). It provides innervation to the terminal colon, the detrusor muscle and the smooth muscles of the genitalia.
• Pudendal nerve is composed of branches from the 3 sacral segments; it is the motor innervation of the urethralis muscle, of the anal striated muscle, of striated muscle of the genitalia. Sensory pathways of perineal region, clitoris or penis run in this nerve.
• Coccygeal nerve provide sensory and motor innervation to the tail.

Lesions

3 nerves lesion:
It is associated with atonic bladder, atonic anal and urethral sphincters; the tail is flaccid with no sensibility; anal and perineal zones loose their sensibility.
Pelvic nerves lesion:
Micturition and defecation problems are serious; cats cannot defecate; detrusor muscle cannot contract and bladder cannot empty. Informations about bladder pressure are not transmitted and micturition reflex cannot occur.
Pudendal nerves lesion:
Anal and urethral sphincters are hypotonic and ineffective; voluntary defecation is lost; sensibility of anal sphincter, perineal region, genital system is lost.
Motricity of anal external sphincter is absent and voluntary miction control is lost. But internal urethral sphincter and muscle organisation of the bladder neck allow continence maintenance;
Coccygeal nerves lesions:
Tail is flaccid and analgesic.

Clinical exam

Neurologic exam must study motricity, sensibility, muscle tone and reflexes:
  • Motricity of the tail, of the anal sphincter.
  • Sensibility of anal and perineal zone.
  • Anal and urethral tone.
  • Bulbocavenous and perineal reflex.
Miction teaches about pelvic nerve function. Residual volume after miction is under 2 ml in the cat.

Classification of cats with sacrococcygeal lesions

Group I
Cats in this group show the following:
Hypotonic tail, without sensibility
• Reflexes, anal tone, perineal pain are normal
• Only coccygeal nerves are injured.
The prognosis for a normal life is excellent in these cats.
Group II
The cats of this group exhibit:
• Flaccid analgesic tails.
• Anal tone, perineal reflex, bulbourethral reflex and perineal pain sensation are normal.
• Although they posture and strain to urinate, they are unable to void urine. Transabdominal attempts to express urine from the bladder are unsuccesful.
These cats begin to urinate after one or two weeks.
In this group, pudendal nerves are functional. The lack of urination is due to an inadequate detrusor contraction coupled with an inadequate urethral relaxation. This disorder of micturition is termed detrusor-sphincter dyssynergia (DSD). It is due to impaired pelvic nerve function.
Group III
• Flaccid and analgesic tail is associated with a depressed anal tone, without a dilated and open anus.
• Perineal pain and anus is absent.
• Perineal and bulbocavernous reflexes are absent or depressed.
• Manual expression of urine is impossible.
For 1 to 4 weeks, the cat does not attempt to urinate. After this time, the cat begins to posture and strain to urinate but the urine is not voided. Four to eight weeks after injury, most cats are able to void and manual expression is easier. They have residual urine volumes of 20 to 50 ml after urinating. Pelvic, caudal and pudendal nerves have been damaged. The pudendal innervation of the striated sphincter remains intact and produces excessive urethral resistance. Prognosis for complete recovery is poor
Group IV
In these group, the cats lost motricity , sensibility and reflexes of the tail and the perineal area. Anus is dilated. Urinary incontinence is present and the cat’s bladder is easyly expressed with abdominal pressure. Group 4 cats have complete interruption of the pelvic, pudendal and caudal nerves. Prognosis is poor.

Therapy

Supportive care is the most important aspect of the treatment. The bladder must be kept empty.
Catheterization is necessary for cats of the groups II and III.
Antibiotics should only be used if bacterial infection is documented.
Drugs to enhance detrusor contractions (bethanechol) could be effective in group II cats.
Drugs to decrease urethral tone (phenoxybenzamine) are disappointing.
Dantrolene has been of some value in cats with excessive urethral tone.

Complications

They include cystitis, pyelonephritis, hydronephrosis. They are caused by a bad management of residual function.