Eight-and-a-half syndrome: An unusual presentation of pontine infarct

56-year-old gentleman presented to the Emergency Department with sudden onset of slurred speech, left sided facial weakness, double vision and dizziness. Clinical examination revealed left lower motor neuron facial nerve palsy, left eye horizontal gaze palsy, adduction paralysis and horizontal nystagmus on abduction of right eye.

Urgent Non-Enhanced Computed Tomography (NECT) brain showed hypodensities at left centrum semiovale, bilateral corona radiata, right lentiform nucleus, and right external capsule suggestive of multifocal multiages cerebral infarcts. No acute infarct seen in the midbrain or pons region.

Subsequent Magnetic Resonance Imaging (MRI) brain done showed T2W/FLAIR high signal intensity with restricted diffusion at left pontine tegmentum in keeping with acute pontine tegmentum infarct. T2W/FLAIR high signal intensity with no restricted diffusion are seen at right corona radiata, right middle cerebellar peduncle and left cerebellar hemisphere suggestive of chronic infarcts.

Eight-and-a-half syndrome is a combination of one-and-a-half syndrome plus ipsilateral
lower motor neurone facial 7th nerve palsy [1]. Clinically one-and-a-half syndrome is characterised by ipsilateral conjugate horizontal gaze palsy (the ‘one’) and an ipsilateral internuclear ophthalmoplegia (the ‘half’) [2]. Internuclear ophthalmoplegia (INO) is recognised by impaired adduction in one eye with dissociated horizontal nystagmus of the contralateral abducting eye secondary to a lesion in the medial longitudinal fasciculus ipsilateral to the eye unable to adduct [3].

Eight-and-a-half syndrome results from lesion in the dorsal tegmentum of caudal pons involving the paramedian pontine reticular formation (PPRF), abducens nucleus, the medial longitudinal fascicles and the facial nerve fascicle on one side [4]. The aetiologies include infarction, demyelination, haemorrhage and tumour [5].

Eight-and-a-half syndrome is largely a clinical diagnosis; however, CT/MRI brain can aid in detecting and differentiating the various underlying aetiologies involving the pons. Computed tomography (CT) remains the first imaging modality requested by clinicians to rule out intracranial pathologies such as infarct, intracranial haemorrhage and tumour.

However, this modality has its limitation in diagnosing hyperacute infarct as seen in our case. MRI is much superior to CT in detecting hyperacute infarcts where infarcted area will demonstrate restricted diffusion on DWI/ADC [6,7]. MRI is also useful in determining other aetiologies causing this syndrome such as demyelinating disease or tumour and appropriate management can be undertaken.

In conclusion, it is of utmost importance to recognise the clinical signs of eight-and-a-half syndrome to be able to initiate proper diagnostic examination, localise the lesion and treat the patient accordingly.

All patient data have been completely anonymised throughout the entire manuscript and related files.