LESIONS

A Guide to Localisation in Neurology

Case 3. Numb face

What is the lesion?

This depends on the location, but a few lesions are worth considering.

Trigeminal gangliopathy could be due to Sjogren’s - an autoimmunoe condition. Facial and oral numbness can be seen. This patient lacks the typical symptoms (dry eyes and mouth, i.e. sicca symptoms ) - but they aren’t always present.

Ganglionopathy can also be caused by paraneoplastic syndromes though not usually in isolation – a much broader pattern of sensory loss is usually seen, accompanied by profound, disabling sensory ataxia and often pain.

Varicella Zoster (shingles) can also affect the trigeminal ganglion, but the more common pattern in shingles is to affect a single branch, especially V3. The features are sensory alteration, pain, and usually a rash, although sometimes there is no rash (i.e. zoster sine herpeticum ).

Isolated trigeminal neuropathy is often idiopathic, with no cause found on investigation. Identifiable causes include compression (e.g. by tumour or blood vessel). Some infections can affect the nerve, such as Lyme disease. In endemic nations, leprosy can affect the nerve.

As discussed, compression by tumour, cyst or blood vessel anomaly at the CPA could affect the trigeminal nerve as it enters the pons. A trigeminal nerve tumour growing here could also cause this (typically a Schwannoma).

However, all of these would usually be slow-growing, so this acute presentation seems unlikely for a root entry zone lesion

A range of brainstem lesions could present with acute hemifacial sensory loss. The most important are below.

Inflammatory demyelination is an important consideration, the commonest cause being multiple sclerosis (MS), and hemifacial sensory loss is a well-known presentation of MS. There are other causes of inflammation in the brainstem such as sarcoidosis, neuromyelitis optica and Behcet’s disease. The tempo of onset – evolving over days – could fit inflammation.

Vascular disease can also affect the brainstem, sometimes causing hemifacial numbness, and sometimes with other features (e.g. gaze palsy). This includes infarction or a small haemorrhage. It’d be unusual for these to affect the components involved in facial sensation and spare other structures (e.g. the cerebellar peduncle in the pons). A brainstem lesion such as a cavernoma, producing a small haemorrhage, could also present in this way.

Mass lesions can produce hemifacial disturbance but the presentation has been short, so only a very aggressive, rapidly growing mass might do this, or alternatively an abscess (but there are no supportive features of this such as fever).

As covered earlier, it seems less likely a lesion here would produce isolated facial/oral numbness - likewise the thalamus and its projections to the brain. Virtually every type of lesion is possible here but important acute causes include vascular and inflammatory lesions.

Again, these are not likely, but vascular or demyelinating lesions are not impossible here, nor is a mass lesion.