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Case Report: Surgical Management of Sub-Arachnoid Cyst in a Yorkshire Terrier

A 2.2kg, twelve-month-old, male, entire Yorkshire Terrier was presented for assessment of generalised ataxia.  Signs were first noted by the owner four months previously, as excoriation of the claws of both thoracic limbs, particularly at slower gait speeds. Survey spinal radiology was performed by the referring veterinary surgeon, but no abnormalities – such as atlantoaxial instability – were detected.

Examination revealed ataxia of all four limbs.  Claws on all limbs appeared scuffed.  There was reduced conscious proprioception of the thoracic limbs and brisk spinal reflexes in all limbs.  Mentation and cranial nerve testing were considered normal, consistent with a spinal cord lesion in the C1-5 segments. 

ALT levels were found to be elevated 429 (0-110)U/l, but resting/ post-prandial bile acids and albumin were found to be within the normal range.  Ultrasound examination of the abdomen, including the liver and associated vessels revealed no structural abnormalities or shunting vessels.  Ultrasound-guided, fine needle aspirates of the liver were normal, with no evidence of microvascular dysplasia.  A haematocrit of 31(37-55)% and cytology of fresh smears were consistent with mild, non-regenerative anaemia.  Coagulation testing was within normal limits.

fig.1 - preoperative, transverse T1W slice at level of subarachnoid cyst, showing right, lateralised fluid-filled space (dark grey) extending ventrally into cord parenchyma

MR-scans of the cervical spine revealed a widening of the cerebrospinal fluids space bordering the right dorsolateral limit of the spinal cord at the level of the Ce2 vertebral body, extending ventrally to compress the cord parenchyma (see fig. 1).  In addition, there was evidence of central canal dilatation/ syringomyelia further caudally consistent with chronic obstruction to the normal flow of CSF.

Treatment

S-Adenosylmethionine (Hepatosyl) was started q24h P.O. to manage non-specific hepatitis.  Repeat biochemistry one week later revealed improvement in ALT levels.  Six weeks later, marsupialisation was performed to drain the cyst;

A right, lateral pediculectomy at C2 was used to access the dura over the cyst.  Durotomy was performed to raise a flap of tissue, which was sutured to the surrounding tissues in an attempt to create a permanent drainage route.  The wound was closed routinely, and the patient made an unremarkable recovery from anaesthesia.  The patient was ambulatory a few hours after surgery and he remained bright and comfortable.

Follow up

Ataxia appeared slightly worse over the following few days.  However, five weeks after surgery, re-examination revealed no further scuffing of the claws and normal thoracic limb proprioception.  There were persistent, mild deficits in the right pelvic limb. 

fig. 2 - five-week post-operative, transverse, T1W slice at level of pediculectomy, showing reduction in size of cyst and increased cross-sectional area of the remaining cord parenchyma as compared to fig. 1

Repeat MR-scans (see fig.2), at the level of the pediculectomy revealed an increase in the cross-sectional area of the cord parenchyma, suggesting surgery was successful in decompressing the cord.

Discussion

The most frequent location for sub-arachnoid cysts is within the limits of the C2 vertebra.   Familial patterns suggest a genetic component so owners should be advised not to breed from affected animals. 

If cysts result in signs early in life, they will often progress over time to compromise the patient significantly as they age.  Corticosteroids at anti-inflammatory doses may be used to slow down the rate of progression but the condition may be managed surgically with the aim of establishing permanent drainage.  However, scarring may limit the long-term effectiveness of surgery and recurrence of signs is possible.

The liver disease present in this case was not thought to be related to the patient’s neurological condition, but nevertheless the patient’s liver biochemistry remains under review.