Intracranial arachnoid cyst

14 Intracranial arachnoid cyst



SIGNALMENT


A 6-month-old male Yorkshire terrier.



CASE PRESENTING SIGNS


Circling, lack of house-training.



CASE HISTORY


The pup had always circled a lot, especially when on the lead or when excited. He was not house-trained and bumped into furniture when running about the house but not when moving at a slower pace. The pup resented handling and would struggle to escape, and bite. Treatment with lactulose syrup and oral Synulox had not improved the clinical signs.



CLINICAL EXAMINATION


The pup was alert and appeared to be responsive to the environment and the owner. The dog circled to the left but did turn to the right on occasion. Slight hypermetria was seen in all limbs which was judged as normal for the breed. Hopping and placing were decreased on the right side. Cranial nerve examination found that the menace response was absent bilaterally and the symmetric pupils were small in ambient light but could dilate in darkness. PLR were normal. An open fontanelle could be felt.



NEUROANATOMICAL LOCALIZATION


The lesion was localized to the left cerebrum, due to the right postural deficits, the circling to the left, small pupils, lack of menace response, and lack of house-training.



DIFFERENTIAL DIAGNOSIS



• Cerebral malformation

• Encephalitis (distemper; necrotizing)

• Metabolic encephalopathy


CASE WORK-UP


Haematology and biochemistry were normal. Post-prandial serum bile acid measurement is a sensitive detector of liver dysfunction and disruption of enterohepatic circulation from a portosystemic shunt. The bile acid stimulation test in this dog was normal. Lack of response to treatment for a suspected portosystemic shunt (PSS) helped to rule out this disease as a probable cause of the clinical signs. The neurological deficits on examination rule out a psychological cause for the circling. Cerebral malformation or inflammation is most likely at that age.


Encephalitis was a possibility. Canine distemper may cause neurological signs in the immunocompromised (e.g. young or unvaccinated) dog several weeks after infection. This acute CNS inflammation results from direct viral injury. Those able to contain the infection and avoid acute inflammation may go on to develop neurological signs later in life. A chronic encephalitis results and is caused by an inflammatory response and subsequent demyelination. Distemper may produce acute encephalitis 1–2 weeks after immunization, with a modified live virus (MLV) vaccine. Neurological signs are variable. Myoclonus is a common sequela.


Necrotizing encephalitis in the Yorkshire terrier typically appears between 1 and 10 years of age, resulting in cerebral and brainstem signs which worsen over several months. The signs in this case appeared to be static. The dog had been vaccinated and had not travelled outside the UK.


MRI of the head found a quadrigeminal cistern arachnoid cyst and enlargement of the lateral and third ventricles. The enlarged cistern may have compressed the midbrain aqueduct, causing secondary dilation of the third and lateral ventricles. CSF cell count, cytology and total protein level were normal.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Intracranial arachnoid cyst

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