Forebrain lesion in the cat: absent menace and circling
13-year-old domestic shorthair cat with progressive behavioural change over 2 months: it walks in wide circles to the right and presses its head against the wall. It walks without ataxia and with normal strength.
| Parameter | Result | Reference |
|---|---|---|
| Menace response | OD normal; OS absent | Present in both eyes |
| Direct and consensual PLR | Normal in both eyes | Normal |
| Palpebral reflex | Normal bilaterally | Normal |
| Postural reactions | Delayed in left limbs | Normal |
Where is the lesion located?
chevron_right Show answer and explanation
A. Right forebrain
Correct. Behavioural change, head pressing and wide circling towards the side of the lesion are forebrain signs. Most optic fibres cross at the chiasm, as do the proprioceptive pathways, so the deficits are contralateral. The pupillary light reflex leaves the visual pathway before the geniculate body, so it is preserved in cortical blindness.
B. Left optic nerve
An optic nerve lesion abolishes the direct pupillary light reflex in the left eye and the consensual response when it is illuminated. Here both are normal, and it would not explain the behaviour or the postural deficits.
C. Left facial nerve
With facial paralysis the cat sees the threat but cannot close the eyelid, and the palpebral reflex would also be absent. Here the palpebral reflex is normal.
D. Left cerebellar hemisphere
The cerebellum can abolish the ipsilateral menace response with normal vision, but it causes cerebellar ataxia (hypermetria, intention tremor), not behavioural change or head pressing.
lightbulb Key takeaway
Forebrain lesion: near-normal gait, wide circling towards the side of the lesion and contralateral deficits (menace, postural reactions, nasal septum sensation). In older cats, meningioma is the most common primary intracranial tumour: MRI is indicated.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.