‘Surgical’ causes of benign intracranial hypertension

Summary

Benign intracranial hypertension is a clinical diagnosis linked to a number of medical and surgical disorders. A common aetiology has not yet been established. It would seem, however, that many, if not all, of these cases can be related to some degree of cerebral venous outflow obstruction. We present here a series of patients with extraluminal compression of the cerebral venous sinuses that has been amenable to surgical resection. These ‘surgical’ causes of BIH illustrate an important subset of the disease and inform us about the possible pathophysiological principles underlying the disorder.

Introduction

Benign intracranial hypertension (BIH) is a clinical syndrome consisting of raised intracranial pressure without any gross structural cerebral abnormality. Persistently elevated intracranial pressure usually leads to chronic headache, and although labelled ‘benign’ the condition may cause papilloedema and eventual blindness. Imaging rules out any intracranial lesion that would cause significant mass effect; there is no hydrocephalus (in fact, ventricular size is frequently small); and examination of the composition of the cerebrospinal fluid is normal.

BIH is therefore a diagnosis of exclusion. It may, however, be associated with a range of medical and surgical conditions (Tables 1 and 2), including obesity, pregnancy, obstruction of cerebral venous outflow, endocrine or metabolic dysfunction, drugs and systemic disease.¹

Table 1.

‘Medical’ causes of BIH (Adapted from Youman's Neurological Surgery¹)

Venous sinus thrombosis	Thrombophilias (antiphospholipid antibody syndrome, antithrombin III deficiency, factor V Leiden deficiency, etc.) Systemic conditions associated with thrombophilia (pregnancy, malignancy, systemic lupus erythmatosus, etc.)
Obesity
Endocrine and metabolic disease	Addison's disease Hypoparathyroidism Hypo/hyperthyroidism Menarche
Drugs	Antibiotics (nalidixic acid, penicillin, tetracyclines) Carbidopa, levodopa Corticosteroids Danazol Growth hormone Indomethacin Ketoprofen Lead Lithium carbonate Oral contraceptives Oxytocin (intranasal) Phenytoin Vitamin A
Systemic illnesses	Anaemia Chronic respiratory insufficiency Familial Mediterranean fever Hypertension Multiple sclerosis Polyangiitis overlap syndrome Psittacosis Renal disease Reye's syndrome Systemic lupus erythmatosus Thrombocytopenic purpurac

Table 2.

‘Surgical’ causes of BIH (Adapted from Owler et al.²)

Primary tumours	Meningioma Plasmacytoma Ewing's sarcoma Dermoid Eosinophilic granuloma
Secondary tumours	Ca prostate metastasis
Trauma	Depressed skull fracture
Infection	Mastoiditis
Vascular malformations	AVM

Although there is no consensus on the precise mechanism of the condition there is increasing interest in the cerebral venous outflow as the common site of abnormality. In support of this concept we present three cases of extrinsic lesions obstructing cerebral venous outflow in patients presenting with features of BIH.

Cases

Case 1

A 21-year-old man presented following a road traffic accident in which he struck the back of his head against a metal pole. He was fully conscious and oriented throughout, with no neurological deficit. A clean occipital laceration was sutured. Within hours of admission he started complaining of headache and blurred vision. This worsened until the third day at which point he could only finger count.

Imaging demonstrated a fracture overlying the torcula with a filling defect on CT venography. The depressed fragment was elevated uneventfully. His headache and visual acuity improved before discharge.

Case 2

A 16-year-old boy presented with a one-month history of worsening headache and vomiting for six days. There were no focal neurological deficits. Fundoscopy revealed bilateral blurring of the disc margins. CT showed erosion of the inner table of the occipital bone near the torcula with filling defect on CT venography. Lumbar puncture demonstrated an opening pressure of 41 cm of water with normal cerebrospinal fluid composition. At craniotomy an extradural mass was excised.

Histopathology demonstrated eosinophilic granuloma. At review two months later the patient was asymptomatic. Follow up imaging confirmed good decompression of the torcula.

Case 3

A 57-year-old man with carcinoma of the ethmoidal sinus was found to have an incidental torcular menigioma. He was asymptomatic at the time of presentation, but some months later developed persistent headache and papilloedema. Further imaging revealed that the tumour had grown and surgery was advised. Via a supratentorial approach the tumour was debulked. Unfortunately a complete resection was not possible as the tumour was adherent to the straight, transverse and sagittal sinuses. Despite this, he made a good postoperative recovery, with resolution of his symptoms.

Discussion

Blood flow through the intracranial venous sinuses may be impeded by a variety of lesions that cause extraluminal compression. This is most vulnerable at the torcula where the superior sagittal, straight and transverse sinuses are confluent. Compression of a single transverse or sigmoid sinus may also prove symptomatic as there is usually dominance of flow to one side, generally the right.

Areas of skull overlying these sinuses can be affected by primary or secondary tumours. Those that have been previously associated with BIH include Ewing's sarcoma, plasmacytoma, metastatic prostatic tumours, epidermoid cysts² and eosinophilic granuloma.³ Depressed skull fractures overlie a venous sinus in 11–18% of cases,⁴ with a proportion going on to develop BIH. This may be immediate or take several months to develop.

The dura mater encloses the venous sinuses. Dural lesions, most commonly meningiomas, can therefore affect venous outflow. When there is significant involvement of a sinus full surgical resection can be extremely difficult. Although the anterior third of the superior sagittal sinus may be safely ligated, posterior to this there is a significant risk of venous infarction and tumour may have to be left or at best diathermized to avoid venous damage.

Infection in the region of the mastoid air sinuses can impair venous flow in the adjacent transverse and sigmoid sinuses. This can either be due to extrinsic

Figure 1.

Case 1. Sagittal CT venogram showing fracture site and filling defect

Figure 3.

Case 3. Sagittal T1 weighted MRI demonstrating supra- and infra- tentorial meningioma compressing the torcula

Figure 2.

Case 2. Axial T2 weighted MRI with contrast showing occipital eosinophilic granuloma

compression by pus or indirectly by inducing venous thrombosis. The first recognized cases of BIH were in patients with chronic suppurative otitis media and mastoiditis that caused widespread morbidity before the antibiotic age.⁵

Conclusion

We present a series of patients with small intracranial lesions insufficient in themselves to cause raised intracranial pressure. Their crucial location directly over the venous outflow channels, however, has given rise to extraluminal compression and consequent intracranial hypertension. These cases clearly illustrate an important link between venous sinus obstruction and BIH.

We have labelled this subset of BIH ‘surgical’ as removal of the compressive lesion has the potential to completely reverse the clinical features. Of course many patients with ‘medical’ causes of BIH end up having surgery in the form of cerebrospinal fluid diversion procedures but this is generally only if initial medical therapies fail.

Footnotes

DECLARATIONS —

Competing interests None declared

Funding None

Ethical approval All patients consented to case publication

Guarantor PAB

Contributorship All authors contributed equally