Journal of the New Zealand Medical Association, 07-August-2009, Vol 122 No 1300
Bilateral trochlear nerve palsies following dorsal midbrain haemorrhage
Sumu Simon, Avninder Sandhu, Dinesh Selva, John L Crompton
Acquired BSO palsy is extremely rare and constitutes 0.48% of nerve palsies affecting the oculomotor, trochlear and abducens nerves.1 One of the authors (JLC), in 30 years of clinical practice has seen 34 patients with acquired BSO palsies. The commonest cause of acquired BSOP is closed head trauma.2 Dorsal midbrain haemorrhage with resultant bilateral SOP is usually associated with other neuro- ophthalmic and neurological manifestations with only 5% of fourth nerve palsies being truly isolated.3
A 37-year-old man had a sudden onset of generalised weakness, double vision, tinnitus, deafness, numbness over the right cheek and tingling over his right arm. He had a history of alcohol abuse. On examination he was found to be alert. Best corrected visual acuity was 6/6 bilaterally. There was no significant head tilt. Cover test revealed slight right hypertropia in primary gaze. Bielshowsky was positive to both sides.
Ocular motility examination revealed limitation of depression in adduction in both the eyes (-2 in the right eye (RE) and -1 in the left eye (LE)) and a V pattern esotropia. There was mild inferior oblique over action in both eyes. He had vertical and torsional diplopia which worsened on down gaze. Double Maddox rod examination demonstrated an excyclotorsion of 15 degrees. He had normal saccades and there was no papilloedema.
Visual field testing was normal. Systemic examination revealed mild nuchal rigidity, bilateral sensorineural deafness, decreased sensation in the maxillary division of the right trigeminal nerve to pain and to light touch and tingling in the right arm. Blood pressure was normal and there were no signs of chronic liver failure.
Computerised tomography showed a non-enhancing 15 mm hyperdense mass in the region of the tectum, obliterating the aqueduct which was consistent with acute haemorrhage. There was also early dilatation of the lateral and third ventricle (Figure 1).
Figure 1. Axial section CT scan showing a well circumscribed hyperdense lesion in the dorsal midbrain (arrow) suggestive of acute haemorrhage.
Magnetic resonance imaging confirmed the presence of acute haemorrhage in the midbrain with perilesional oedema and obstructive hydrocephalus. An audiogram revealed a mild high tone sensory neural loss with the right side hearing slightly worse than the left. Routine blood investigations were normal (platelet count 366x10 9/L). He had an altered lipid profile (total triglycerides 4.1mmol/L, total cholestrol 8.4 mmol/L, HDL 1.1 mmol/L, LDL 5.4 mmol/L).
The liver function tests were normal except for elevated levels of gamma glutamyl transpeptidase (116U/L). He was started on dexamethasone 2 mg twice a day which was tapered over the next three days. His diplopia resolved over five weeks. The facial numbness and upper limb tingling improved over a week. The deafness and tinnitus resolved six months later. He was followed up periodically with MRI over two years (Figure 2) which showed near total resolution of the haemorrhage with no evidence of an underlying lesion.
Figure 2. MRI scan at 2 years follow up. An axial T1-weighted image shows near total resorption of the haemorrhage in the dorsal midbrain (arrow) with normalisation of the ventricles
Spontaneous bilateral SOP from midbrain stroke with no other associated ocular signs has been reported only once before,4 and we are unaware of any other detailed clinical description in the English literature. The cause of spontaneous midbrain haemorrhage is often unclear; the commonest cause being vascular malformation.5 The cause for the haemorrhage in our patient may have been due to a bleed from a cavernous haemangioma or cryptic arteriovenous malformation.
The bilateral sensorineural loss was probably due to the involvement of the inferior colliculi.6 Although no cause for the other neurological deficits was detected on imaging, a plausible explanation is that the bleed and resultant perilesional oedema could have caused a restricted sensory syndrome. The diagnostic dilemma in this case would be an alternating skew deviation but the arguments in favour of double fourth nerve palsy are the impaired ductions in the domain of the superior oblique, V pattern esotropia and significant excyclotorsion. The other reported non traumatic causes of isolated double fourth nerve palsy include intracranial inflammations, arachnoid cysts, neoplasms, post infectious neuritis, mononeuritis multiplex, hydrocephalus and multiple sclerosis.7–13
Both CT and MRI are accurate and non invasive investigations, with CT being more useful to diagnose an acute haemorrhage while MRI is the preferred investigation to monitor the evolution. Management is usually conservative. Exploration and shunting can be done in patients with progressive deterioration and hydrocephalus respectively.5
In conclusion, non-traumatic isolated bilateral SOP are indicative of pathology in the midbrain, specifically a dorsal midbrain lesion. Appropriate imaging with CT and/ or MRI should be performed on a semiurgent basis in order to make an accurate diagnosis and to lead to appropriate advice and treatment.
Author information: Sumu Simon1; Avninder Sandhu2; Dinesh Selva1;
John L Crompton1
South Australian Institute of Ophthalmology and Discipline of Ophthalmology and Visual Sciences1 & Department of Radiology2
Royal Adelaide Hospital, Adelaide, Australia
Correspondence: Sumu Simon, South Australian Institute of Ophthalmology, Level 8, Royal Adelaide Hospital, North Terrace, Adelaide-5000, Australia. Email: firstname.lastname@example.org
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