Spontaneous Intracranial Hypotension Causing A Partial Third Cranial Nerve Palsy: A Novel Observation

Introduction

Spontaneous intracranial hypotension (SIH) has been recognized for over half a century (1) and associated cranial nerve palsies have been frequently described (2–5). However, there has as yet been no unequivocal report of an isolated third nerve lesion due to SIH. The following account is the first report of such a case.

Case report

A previously fit 26-year-old male presented with a sudden severe occipital headache preceded by a sensation described as ice-cream running onto the back of his neck for a few seconds. The headache was exacerbated by sitting or leaning forward and was relieved by lying flat. The next day his colleagues noticed that he had a dilated right pupil and ipsilateral partial ptosis, although the headache had improved a little. He denied diplopia but had mild problems of ‘visual perception’ that interfered with reading. There had been some dizziness and vomiting. When examined, external ocular movements were all completely normal. However, the right pupil was slightly dilated but reactive to light, both directly and consensually.

With a working diagnosis of possible subarachnoid haemorrhage he proceeded to a computed tomography of the head which was normal. A lumbar puncture was performed in the left lateral position. Cerebrospinal fluid (CSF) was obtained at the second pass with an opening pressure of 2 cm water. Subarachnoid haemorrhage was excluded on the basis of a sequential reduction in the red cell count from 339/mm³ in the first sample to 13/mm³ in the third. No samples had any white cells and CSF glucose was normal. Unfortunately, CSF protein analysis was omitted. He was discharged home.

The pupil diameter continued to fluctuate with ‘blurring of vision’, although the headache remained quiescent. He returned 10 days after the initial ictus following a second sudden onset of severe biparietal headache, again described as a crushing pressure. Although its clinical features were similar to the first, the postural nature of the headache was less obvious. Clinical findings remained the same.

There was clinical concern for an unruptured aneurysm and despite a subsequent normal magnetic resonance imaging (MRI) brain scan and magnetic resonance angiography of the circle of Willis, it was felt necessary to proceed to a definitive right carotid angiogram. Again this was normal. Even on subsequent later review, including real-time recordings of the angiography, all imaging was unremarkable.

In the following month the headache remained mild and gradually disappeared. However, he complained of general tiredness and shortly after discharge had four episodes of prolonged periods of sleep (lasting 36 h). There were bouts of nausea and vertigo and on two or three occasions this woke the subject from sleep but settled after 1 h. This perception of the environment spinning was made worse by an upright posture. Two months after the initial event the patient became aware of reduced hearing on the left side with an intermittent whistle in that ear. This persisted for approximately 1 month. It was only at this stage, 3 months after the onset, that the fluctuating pupillary dilation and associated blurring ceased.

Such was the distraction from all of these symptoms, it precluded his return to work and resulted in a profound change in his temperament requiring treatment with fluoxetine.

In retrospect he was aware of four episodes in the last 4 years of an odd gush of sticky liquid from one nostril, lasting 10 min on each occasion, but not blood. The last such episode had been at least 1 year earlier with no such event preceding the headaches. However, repeat MRI of the brain with gadolinium enhancement failed to reveal any sites of CSF leakage.

Discussion

Having first described the condition in 1938 as ‘spontaneous aliquorrhea’, Schaltenbrand (1) gave a summary of SIH including the clinical presentation and the pathological consequences from which imaging changes could be predicted. Christoforidis et al. (6) reviewed 40 cases in the literature, listing the most frequent clinical, laboratory and imaging findings. Although imaging abnormalities, CSF pleocytosis and raised CSF protein have been described in SIH (7), their absence in this case does not preclude the diagnosis and its clinical characteristics are in keeping with SIH. Symptomatic intracranial hypotension has been described without the presence of meningeal enhancement on MRI (8, 9), and the finding of a lumbar opening pressure <50 mm H₂O in this case strengthens the diagnosis. The headache, initially aggravated by an upright posture progressing to a lingering chronic daily headache (10), was also typical, as was the trouble focusing vision and difficulty reading, and auditory and vestibular symptoms. Importantly, alternative causes for acute severe headache with cranial nerve palsy such as subarachnoid haemorrhage were excluded.

Abducens nerve palsies have been frequently observed in SIH (2–5), as has sudden deafness (4). Ferrante et al. (11) reported a 55-year-old woman with a mild paresis of the right 3rd and 6th cranial nerves as well as severe paresis of the left 6th nerve. However, the case was complicated by possible alternative causes including diabetes and previous cerebral infarction. Further, despite transient MRI features the definitive diagnostic test of CSF opening pressure was obscured by the fact that the lumbar puncture was performed in a sitting position and the opening pressure was 10 cm H₂O, later rising to 34 cm H₂O. Without a low CSF pressure on the initial lumbar puncture, the ‘diagnosis is difficult to make with confidence’ (2). It is possible that the pressure measured in the current case was falsely low following an initial failed attempt, which could have resulted in an extradural pooling or reservoir of CSF. However, this is unlikely.

Apte et al. (3) proposed that descent of the brain may secondarily cause stretching of the abducens nerve along its complicated intracranial course and manifest as a sixth nerve paresis with diplopia on ipsilateral gaze. It must be assumed the third nerve palsy here represents a further false localizing sign relating to pressure gradients within the central nervous system and resultant downward movement of intracranial contents. Silberstein explained the absence of diffuse meningeal enhancement on MRI in SIH as occurring only when there is a CSF leak and not when low pressure is due to other mechanisms (12). In the current case a CSF leak was unlikely and hence an absence of acute imaging abnormalities.

The absence of imaging and CSF abnormalities is an important finding in this case, underlining that the diagnosis of SIH must rely upon clinical features and measurement of lumbar puncture opening pressure. SIH may well be under-reported and overlooked. The presence of 3rd or 6th cranial nerve palsies in combination with sudden onset headache should make the clinician suspicious of the diagnosis and it should be considered after acute severe headache once aneurysmal subarachnoid haemorrhage has been excluded.