Acoustic neuroma presenting as a hypnic headache

Abstract

Hypnic headache (HH) is a rare, primary headache syndrome that invariably occurs during sleep and wakes the patient. Acoustic neuroma (AN) is a benign tumour that uncommonly presents with isolated headache. Here, we describe a patient with AN that presented with an HH-like syndrome. A 40-year-old woman presented with 4 months of generalised, throbbing, nocturnal headaches that woke her from sleep. Neurological examination was unremarkable. Retrospectively, she reported a 4-year history of mild, bilateral tinnitus. Neuroimaging demonstrated a large, left-sided AN in the cerebellopontine angle without obstructive hydrocephalus. Gamma knife radiosurgery controlled tumour growth. One year after radiosurgery, she became nocturnal headache-free. AN has not previously been described as presenting with an HH-like syndrome. There are four previous reports of an HH-like syndrome secondary to intracranial masses. In all cases, patients became headache-free following surgery. This advocates for neuroimaging to exclude structural causes.

Background

Hypnic headache (HH) is a rare, primary headache disorder that has been described in case reports and series since 1981.¹ It is considered idiopathic and few cases have described it in association with structural lesions. Here, we describe the case of a 40-year-old woman presenting with the features of probable HH secondary to an acoustic neuroma (AN).

Case presentation

A 40-year-old woman presented to neurology clinic with a 4-month history of headaches that woke her from sleep. These occurred stereotypically 2 hours after falling asleep. They were described as severe, holocranial headaches that were throbbing in character. They were associated with mild nausea, neck pain and stiffness. They were relieved by activity and subsided after 30 min. However, on falling asleep again, they would recur, leading to a disrupted sleep pattern and daytime somnolence. At their most frequent, she was having up to three attacks per night on 4 days per week.

She had a history of migraines that were always unilateral, throbbing in character and of moderate intensity. They typically lasted 1–2 days, were associated with nausea and were exacerbated by activity. Her migraines could occur in the morning after waking but never woke her from sleep. These occurred 6–8 times per month and were more frequent at the time of menstruation. She also had a history of motion sickness, especially on water. Prior to seeing a neurologist, she had been to a physiotherapist and a cervicogenic cause had been excluded. She was otherwise well with no other significant medical or family history. Her neurological examination was unremarkable.

Her headaches were treated symptomatically with magnesium and acupuncture. She was encouraged to avoid conventional analgesics to avoid medication overuse headache. Given the history of new-onset headache that was characteristically different from her migraines, she was referred for neuroimaging.

Investigations

She underwent a contrast-enhanced MRI scan which showed a large, left-sided cerebellopontine angle mass, consistent with AN. She was, therefore, referred to neurosurgery. On further questioning after its discovery, she retrospectively reported a 4-year history of occasional, mild, non-progressive and bilateral tinnitus. This had had negligible impact on her daily life and had been hardly noticed by the patient. Her bedside hearing assessment, including free field and tuning fork tests, was normal so no formal audiology assessment was undertaken.

The lesion was characterised as a 31 ×27×23 mm AN extending into the pons with a small gap between the distal tumour and modiolus of the cochlea (figure 1). The total volume of the tumour was calculated as 9.86 cm³.

Figure 1.

T1 axial (A), coronal (B), sagittal (C) with contrast and T2 axial (D) MRI sequences, showing a 31× 27 mm acoustic neuroma in the left cerebellopontine angle, with no obstructive hydrocephalus.

Treatment

The options of watching and waiting, surgery or gamma knife radiosurgery were discussed with the patient. Given the size of the lesion, the neurosurgeon did not feel it appropriate to watch and wait. However, given that her hearing was intact, it was felt that on the balance of risk versus benefit, radiosurgery would be the safest approach in attempting to preserve her hearing and facial nerve function. Immediately following radiosurgery, she experienced some non-specific weakness and balance disturbance in her lower limbs, but without functional limitation and with a normal neurological examination. These symptoms resolved by her next follow-up.

Outcome and follow-up

The radiosurgery was successful in controlling the growth of the tumour. Her 6-month follow-up MRI showed stable tumour size with typical loss of contrast enhancement and cystic changes postradiosurgery, and her 18-month scan was consistent with control of tumour growth following radiosurgery (figure 2).

Figure 2.

T1 post-contrast (A–C) and T2 MRI (D–F) sequences showing tumour size at presentation (A, D), with control of growth and typical post-radiosurgery changes at 6 months (B, E) and 18 months follow-up (C, F).

In the months following radiosurgery, she reported a gradual reduction in the frequency and severity of her nocturnal headaches. At her neurological follow-up 6 months after radiosurgery, she was completely nocturnal headache-free and discharged herself from further review. She remained under follow-up of her neurosurgeon and at 18 months she remained nocturnal headache-free.

Discussion

HH is a rare headache disorder with only several hundred reports since its first description in 1988.¹ It presents with a mean onset of 60 years and a slight female preponderance.² Up to 70% of patients have a history of migraine.³

The diagnosis of HH according to the International Classification of Headache Disorders third Edition (ICHD-3) requires it to be a primary headache that is dull in nature, develops only during sleep and wakes the patient up, occurs at least 10 times per month for more than 3 months with each episode lasting at least 15 min, and has no autonomic features or restlessness.⁴ As a primary headache disorder, by definition other causes such as hypertension, obstructive sleep apnoea, hypoglycaemia and intracranial disorders must be ruled out. Were it not for the finding of the AN, the features of this case would meet the ICHD-3 criteria for probable HH. This highlights the importance of neuroimaging to exclude structural causes that may mimic HH.

There are few reports of an HH-like syndrome in association with structural lesions. There have been two previous reports in association with pituitary adenomas,^{5 6} one report of cerebellar haemangioma⁷ and one posterior fossa meningioma.⁸ This is the first report of HH-like syndrome in association with AN.

The pathophysiology of HH is unclear, but functional neuroimaging suggests involvement of pain processing areas and the hypothalamus. Electroencephalography shows occurrence in both rapid eye movement (REM) and non-REM sleep.⁹ One might speculate that tumours in the pituitary might have a disruptive effect on sleep by either direct compression of the hypothalamus or secretion of hormones that may disrupt circadian rhythms.

The predominance of posterior fossa tumours in two previous report, as well as our own, might suggest an obstructive effect with possible raised intracranial pressure (ICP). This would explain a nocturnal headache that worsens on lying down and is relieved by waking and getting up. However, in only one of these cases was there evidence of slight ventricular dilatation.⁸ There was no clinical evidence of raised ICP, for example papilloedema, nor radiological evidence of obstructive hydrocephalus in our case.

AN is a slow-growing, benign neoplasm that most commonly arises from Schwann cells of the superior vestibular nerve. It accounts for 80% of cerebellopontine angle tumours, with the remainder being meningioma, facial nerve neuromas and others. Its reported incidence is 1 in 100 000 but post-mortems suggest that it is under diagnosed. Ninety-five per cent of cases are sporadic, with the remainder secondary to inherited genetic disorders such as neurofibromatosis type 2.¹⁰

AN most frequently presents with unilateral hearing loss (80%), tinnitus (63%), ataxia (4%) or vertigo (3%). Uncommonly, AN can present with a generalised headache (2%).¹¹ Headache also appears to be a discriminating factor for large tumours (greater than 30×20 mm).¹² However, where headache is present, it is usually an associated rather than an isolated presenting symptom.¹³ There are no previous reports of a nocturnal headache, making this case a novel presentation of AN.

One could argue that perhaps the onset of subtle tinnitus 4 years preceding the headache may have heralded the beginning of growth of the tumour, and as it grew larger it led to the development of a new headache. Against this would be that these symptoms were bilateral, occasional, non-progressive and subtle enough that they were only mentioned on specific enquiry after discovery of the tumour, which makes them of unclear significance. The widespread prevalence of mild tinnitus in the general population (up to 18%)¹⁰ makes it difficult to specifically associate the symptoms with the emergence of this patient’s lesion. Pulsatile tinnitus can also be a feature of raised ICP. However, in this case, the tinnitus was not pulsatile and there was no clinical nor radiological evidence of raised ICP. The motion sickness in her history is a common finding in migraineurs. Additionally, the presence of vestibular symptoms in migraineurs is common, occurring without headache in 30% of episodes.¹⁴

Management of AN may involve watchful waiting with serial yearly MRI to monitor growth, surgery or stereotactic radiosurgery via gamma knife, which delivers highly localised radiotherapy to the lesion. In the four previous reports of HH-like syndromes secondary to an intracranial mass, all patients were noted to become headache-free following surgery (table 1).^5–8 This is consistent with our case, whereby the patient’s nocturnal headaches improved in both severity and frequency, and by 6 months after radiosurgery she was nocturnal headache-free.

Table 1.

HH-like syndromes associated with structural causes, management and outcomes

Report	Lesion	Management	Outcome
Garza and Oas 20095	Non-functioning pituitary adenoma	Transphenoidal resection	Asymptomatic at 6 months
Valentinis et al 20096	Growth hormone-secreting pituitary adenoma	Transphenoidal resection	Asymptomatic at 1 year
Mullally and Hall 20107	Cerebellar haemangioma	Craniotomy and resection	Asymptomatic at 1 year
Peatfield and Mendoza 20038	Posterior fossa meningioma	Craniectomy and resection	Asymptomatic at 3 years
Present study	Acoustic neuroma	Gamma knife surgery	Asymptomatic at 6 months

HH, hypnic headache.

Large intracranial tumours may give rise to headaches through local vascular congestion or meningeal irritation through stretching. Radiosurgery is capable of reducing tumour and non-tumour local vascularity,¹⁵ as well as controlling meningeal stretching through growth control. It is possible then that the resolution of headaches following radiosurgery in our case was through this mechanism.

It is possible that the AN in this case could have been an incidental finding on neuroimaging, that is, an ‘incidentaloma’. However, this would not explain why the patient became nocturnal headache-free after radiosurgery, which suggests a more causal relationship. Indeed, this syndrome would satisfy the ICHD-3 criteria for headache secondary to intracranial neoplasm, in that it is a ‘headache that has developed in temporal relation to the neoplasm, or led to its discovery’ and that the ‘headache has significantly improved in temporal relation to successful treatment of the neoplasm’. [4%5D Furthermore, incidence data of truly asymptomatic, ‘incidental’ ANs suggest they are rare (0.02%).¹⁶ Taken together, these arguments suggest that it is more likely that the AN was causally related to the development of our patient’s new headaches.

Conclusion

Although HH is a primary headache disorder, as many as 1% of HH-like syndromes will have a structural cause. We advocate for the use of neuroimaging to rule out a structural lesion, as operative management of the underlying lesion may lead to complete symptom resolution.

Learning points.

• Hypnic headache (HH) is a dull, generalised and throbbing headache that invariably wakens the patient from sleep.

• It is a primary headache disorder but as many as 1% of HH-like syndromes will have an underlying structural cause.

• Acoustic neuroma uncommonly presents as headache syndrome and the presence of headache suggests a larger tumour.

• Careful evaluation may reveal the presence of subtle audiovestibular symptoms such as tinnitus that may precede the headache by years.

• Neuroimaging should be performed to exclude a structural cause of nocturnal headaches, as treatment of the underlying cause may lead to complete symptom resolution.