Case presentation:
A four month old male German Shepherd puppy presented with a history of frequent generalised seizures for about 3 weeks, with some odd episodes of standing still and crouching, and some salivation. Neurological examination was unremarkable.

Question. What is your neurolocalistion?
Question. What are your most likely differentials?

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Investigations
Routine haematology and biochemistry, faecal examination by Baermann's technique for lungworm, dynamic bile acids and serology for Toxoplasma/Neospora  were all normal.

Imaging
MRI showed  a severe left sided brain malformation with the caudal left hemisphere replaced by CSF. See figs 1 and 2 below.

Fig 1. (above) T1 weighted parasagittal MRI of the brain, showing CSF in the region where the caudal cerebral hemisphere should be.

Fig 2. Transvese T1-weighted MRI showing CSF in place of cerebral tissue on the left.

Treatment
Levetiracetam was chosen as an initial treatment for its quick onset of activity. The prognosis was suspected to be poor.

Outcome
No further seizure activity was observed for 7 days. The puppy was  unfortunately found dead one morning, soon after this.

Post mortem examination
A small defect in the calvarium was noted, which was covered in meninges (fig 3). The gross post mortem findings were as expected from the MRIs, with the caudal third of the the left cerebral hemisphere missing, replaced with CSF (fig 4). Histology of the brain also showed evidence of acute meningitis.

Fig 3. Post mortem examination of the puppy. The scissors are pointing to a defect in the calvarium covered by meninges.

Fig 4. Post mortem examination showing the small left cerebral hemisphere (on the right of this picture)

Final diagnosis
Porencephaly, with acute meningitis

Discussion
Porencephaly is a rare developmental condition in which a cavity is found in the skull in place of part of the cerebral hemispheres. In this case, the main signs were seizures, which are a common manifestation of forebrain lesions. Some behavioural abnormalities in this case could also be attributed to the forebrain disease. There is no specific treatment. Intracranial pressure is not elevated, so ventriculoperitoneal shunting is not indicated. Management of the condition is aimed at control of clinical signs. The prognosis is poor however. This case was further complicated by the surprising post-mortem discovery of acute meningitis. The cause and significance of this is not known. A CSF tap was not performed, because of initial fears regarding possible raised intracranial pressure making the procedure more dangerous. Whether treatment of the meningitis would have led to a better long term outcome in this case is debatable.

First published Thu, Mar 10 2011