Idiopathic intracranial hypertension (IIH) is a disease of unknown aetiology, which is associated with increased intracranial pressure. It predominantly affects obese women of childbearing age. There is increased intracranial pressure without hydrocephalus or mass lesion, with normal cerebrospinal fluid composition. The common presenting symptom is headache caused by intracranial hypertension. It is a diagnosis of exclusion in a pregnant woman presenting with headache. This article aims to provide an overview of the current issues associated with idiopathic intracranial hypertension in pregnancy.
In 1893 Heinrich Quincke reported the first recorded cases of intracranial hypertension of unknown cause and described them as ‘meningitis serosa’. Subsequently in 1904 Nonne coined the term ‘pseudo tumour cerebri’ and described this condition with symptoms associated with intracranial tumours but with an unusual course of remission. In 1955, Foley termed this condition ‘benign intracranial hypertension’. In view of the serious consequence of visual loss, the term benign intracranial hypertension was changed to idiopathic intracranial hypertension.
Incidence of idiopathic intracranial hypertension
IIH has a female to male ratio of 8:1. The incidence of IIH in women of childbearing age is about 0.9/100 000, which increases to 19.3/100 000 in obese women. The prevalence of obesity in pregnancy increased from 9–10% in the early 1990s to 16–19% in 2000. With increasing prevalence of obesity in pregnancy, the incidence of IIH in pregnancy is also likely to rise.
Pathogenesis and clinical features of idiopathic intracranial hypertension
The pathogenesis of IIH remains unclear. It is thought to be caused by disordered cerebrospinal fluid (CSF) dynamics. It is unclear from the evidence as to whether it results from enhanced CSF production at the choroid plexus or restricted CSF drainage at the arachnoid granulation tissue.
Common symptoms include headache and transient visual obscuration. The headache can occur daily and is typically a throbbing, retrobulbar headache that can worsen with eye movements. It may be associated with nausea, vomiting and photophobia. Visual obscuration can last for a few seconds and may be partial or complete. Other visual symptoms include visual blurring, visual loss and double vision. This condition may aggravate pre-existent migraine. Patients with IIH can also present to the ENT surgeon with tinnitus, vertigo and, rarely, spontaneous CSF otorrhoea or rhinorrhoea.
Common signs of IIH include papilloedema (optic disc swelling that is caused by increased intracranial pressure), visual field defect with enlarged blind spot, reduced visual acuity, reduced colour vision and sixth nerve palsy. Sixth nerve palsy is a false localising sign and occurs as a result of stretching of the nerve in its long intracranial course. This has been noted in more than 10% of patients with IIH. There is no direct correlation between visual symptoms and the severity of papilloedema.
Diagnosis of idiopathic intracranial hypertension
The diagnostic characteristics of IIH were first postulated by Dandy in 1937. These were later formulated into a set of diagnostic criteria (Box 1) by Smith in 1985.[2, 13]
Box 1. Modified Dandy criteria
Signs and symptoms of increased intracranial pressure: headaches, nausea, vomiting, transient obscurations of vision, papilloedema
No localising neurologic signs otherwise, with the single exception being unilateral or bilateral sixth nerve paresis
Cerebrospinal fluid can show increased pressure, but no cytologic or chemical abnormalities otherwise
Normal to small symmetric ventricles must be demonstrated (originally required ventriculography, but now demonstrated by computed tomography scan)
The lumbar CSF opening pressure should be greater than 250 mmH2O measured with the patient in the lateral decubitus position to diagnose IIH. The CSF opening pressure measurements and constituent assay are vital to confirm the diagnosis of IIH.
Neuroimaging in the diagnosis of IIH
Neuroimaging is essential to exclude other causes such as hydrocephalus, mass or structural lesion. A report on diagnostic criteria for IIH suggested that a computed tomography (CT) scan is adequate to exclude hydrocephalus and mass lesions. However, other causes of intracranial hypertension such as venous sinus thrombosis are not detected on an unenhanced CT scan. Further imaging with magnetic resonance imaging may be required in such conditions. A prospective study evaluated the use of magnetic resonance venography in women with IIH and concluded that magnetic resonance venography may be useful in atypical cases of IIH.
Idiopathic intracranial hypertension and visual function
The ophthalmic finding of raised intracranial pressure is papilloedema. Raised CSF pressure is transmitted through the optic canal into the intraorbital optic nerve sheath. This results in papilloedema (nerve fibre swelling at the nerve head), which can be asymmetrical. Papilloedema is usually assessed by fundoscopy or disc imaging techniques.
Severe visual loss may complicate IIH between 10% and 20%. Quantitative serial perimetry is mandatory for monitoring clinical progress to assess the visual field.
Typically, central vision is preserved and perimetry shows enlargement of the blind spot. Peripheral field and central acuity are at risk in many cases. Central acuity may be preserved with marked peripheral field constriction, which may be overlooked. A high index of suspicion should be maintained in monitoring these patients.
Effects of idiopathic intracranial hypertension on pregnancy
A case review in 1972 commented that termination of pregnancy must be considered in worsening visual impairment or with exacerbation of IIH in previous pregnancy. This has since been disputed with the newer modalities of treatment. Termination of pregnancy is not warranted in IIH as it does not alter the course of pregnancy. There is no increased incidence of obstetric complications in women with IIH.
Mode of delivery
There is insufficient evidence regarding the safe mode of delivery in women with IIH. A case series of idiopathic intracranial hypertension in pregnancy has reported more than 50% incidence of term vaginal deliveries. The increase in intracranial pressure that occurs during labour is transient and is not harmful to the mother or baby. A caesarean section is not routinely required. The mode of delivery needs to be determined by obstetric factors only.
Effects of pregnancy on idiopathic intracranial hypertension
There have been isolated case reports that implicate pregnancy as a risk factor. A controlled study by Digre et al. has confirmed that pregnancy is not an aetiologic factor. Pre-existing IIH tends to worsen in pregnancy, probably as a result of the weight gain.
Visual outcome for pregnant women with IIH is similar to that for non-pregnant women. Subsequent pregnancy is not implicated as a risk factor for recurrence of IIH.
Clinical features and safety of diagnostic procedures in pregnancy
IIH tends to present in the first half of pregnancy but cases of IIH have been reported in the third trimester as well. The prevalence of pregnancy in IIH women ranges from 2% to 12%. Women with IIH in pregnancy usually present with severe headache. The diagnosis of IIH is confirmed using modified Dandy criteria (Box 1).
CSF evaluations by lumbar puncture can be performed safely and interpreted easily during pregnancy. It is safe to have CT evaluation in pregnancy as the fetal dose of ionising radiation during a head CT scan is significantly low (<0.005 mGy), while an accepted background cumulative dose of ionising radiation during pregnancy is 50 mGy. However, gadolinium-based contrast media that are used in magnetic resonance imaging can cross the placenta and are proven to be teratogenic at higher doses in animal studies. The European Society of Radiology guidelines state that gadolinium can be used in pregnant women. Therefore the risks and benefits of enhanced magnetic resonance imaging examination should be discussed with the woman before imaging.
Headache in pregnancy
The headache caused by IIH in pregnancy must be differentiated from other causes. The International Classification of Headache Disorders divides headache into three categories (Box 2). The symptom of headache in a pregnant woman must be considered seriously and a systematic approach is essential (Figure 1). Detailed history with regard to the site and severity of headache will help to identify the cause. Symptoms of visual disturbances, vomiting and neck stiffness may indicate significant neurological causes. Past psychiatric and drug history (caffeine, opioid, cannabis and cocaine) indicate secondary headaches. Life-threatening complications such as eclampsia, cerebral venous thrombosis and meningitis need to be excluded. Examination of the eyes, ears, nose, throat and neck is important to rule out secondary causes of headaches. Imaging techniques are necessary to exclude intracranial tumours and thrombotic events. Figure 1 summarises the assessment process when pregnant women present with headache.
Box 2. Three categories of headache
Primary headaches: migraine or tension headaches – these are the common causes of headaches in pregnant women
Cranial neuralgias, central and primary facial pain and other headaches
Treatment of idiopathic intracranial hypertension in pregnancy
The treatment of IIH in pregnancy is the same as in the non-pregnant state. Care must be multidisciplinary and should involve the neurologist, obstetrician, anaesthetist and ophthalmologist. The main goals of treatment are symptom control and preservation of vision.
Medical treatment options comprise analgesics for headache, diuretics to reduce CSF production and dietary modification to aid weight loss. Surgical treatment options include repeated lumbar punctures, optic nerve sheath fenestration and CSF diversion procedures.
Diet and weight control
Marked weight gain may be a predictor of visual function deterioration and papilloedema. It is ideal for women with IIH to restrict their weight gain to 20 lb during the pregnancy. In a series of 12 pregnant women with IIH, weight control using a non-ketotic diet with moderate salt and caloric restriction improved visual symptoms and visual field loss in three patients.
Simple analgesics such as paracetamol are safe to use in pregnancy. A risk–benefit analysis must be considered with opioids because they can cross the placenta. Regular use during pregnancy may cause physical dependence in the fetus, leading to withdrawal symptoms in the neonate. The use of non-steroidal anti-inflammatory drugs in later pregnancy is associated with premature closure of the fetal ductus arteriosus and oligohydramnios, therefore they should be avoided during the third trimester.
Acetazolamide inhibits carbonic anhydrase enzyme in the central nervous system, which delays abnormal and excessive discharge of CSF from the choroid plexus. It is a category C drug (animal studies have shown adverse fetal effects and there are no well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks). Observational case series[26, 27] reported no adverse effects when acetazolamide was used in pregnancy including the first trimester. Loop diuretics act by inhibiting cerebrospinal fluid production. There are no adverse fetal effects associated with loop diuretics when used for a short period of time. Thiazide diuretics such as hydrochlorothiazide should be avoided due to risks of fetal growth restriction.
Corticosteroids are used occasionally in the treatment of IIH, but their mechanism of action is not clear. It is recommended that corticosteroids be used only in an acute clinical presentation to minimise any potential side effects.
Current surgical treatment options include optic nerve sheath fenestration, and CSF shunting via the lumboperitoneal or ventriculoperitoneal route. These are indicated if there is worsening of visual function in spite of medical treatment. Optic nerve sheath fenestration is indicated in acute deterioration of optic nerve function resistant to CSF diversion. It is safe in pregnancy.
There is little evidence for stenting of the transverse intracerebral venous sinus. It has been undertaken in the rare event of cortical venous hypertension. Other neurosurgical procedures such as subtemporal decompression of the optic nerve can be considered in complex cases.
A Cochrane systematic review on interventions for IIH highlighted the lack of randomised controlled trials on the treatment modalities. It concluded that there is insufficient information to generate an evidence-based management strategy for idiopathic intracranial hypertension.
Repeated lumbar puncture is safe and can be done at any time during the pregnancy to reduce the CSF opening pressure. Repeated lumbar puncture has been proven to improve visual symptoms and headache. The frequency of lumbar puncture depends on the severity of IIH. In the acute stage, it can be done daily if required. However, it can be technically challenging in an obese pregnant woman.
Shunts and pregnancy outcome
There are limited data available on pregnancy outcome in women with neurosurgical shunts. Landwehr et al.reviewed 25 pregnancies with a shunt in place and commented on the mode of delivery. There were 13 pregnant women with IIH who had a lumboperitoneal shunt. There were five term vaginal deliveries in this group without any anaesthetic complications. It is recommended to consider continuing neurological symptoms and patient preference to decide on mode of delivery in these women.
Anaesthetic implications in idiopathic intracranial hypertension
Spinal anaesthesia is safe for women with IIH. Epidural anaesthesia carries a potential risk of increasing intracranial pressure with a large volume of drugs in the epidural space. Particular attention must be paid to women with a lumboperitoneal shunt who need regional anaesthesia. There is a potential risk of shunt damage. Prior imaging is recommended because there is a risk of shunt entanglement. General anaesthesia carries a risk of increasing intracranial pressure with rapid sequence induction.
Monitoring pregnant women with idiopathic intracranial hypertension
Women with IIH must be monitored closely throughout the pregnancy jointly by the multidisciplinary team. Neurology and ophthalmology reviews must be undertaken regularly in pregnancy. Review in an obstetric anaesthetic clinic is recommended to discuss the implications of analgesia in labour. Growth scans are required for obstetric indication alone. The frequency of visual field testing depends on the symptoms. If the patient's visual symptoms are stable, visual field testing may be done every 2–3 months. However, any change in vision should be brought to immediate medical attention.
Postpartum implications of idiopathic intracranial hypertension
Acetazolamide can be continued during breastfeeding. A review on analgesics and breastfeeding stated that paracetamol and short-term use of NSAIDs are safe to use. Ibuprofen is the drug of choice if long-term use is contemplated.
Women with IIH must be adequately counselled about the benefits and risks of hormonal contraception. There are case reports associating IIH and progestogen-only contraceptives. The recommendation is to liaise with neurologist and ophthalmologist regarding progestogen only contraception.[31, 32]
The course of IIH is variable in pregnancy. Women with IIH who are planning pregnancy will benefit from prepregnancy counselling. Review of medication and weight loss will help to reduce complications in pregnancy. Multidisciplinary care is essential in managing pregnant women with IIH. The investigation and treatment modalities are safe in pregnancy. IIH is not associated with adverse pregnancy outcome and vaginal delivery is possible in women with the condition.
Disclosure of interests
None to declare.
Contribution to authorship
LT and KR contributed to the literature search; writing up the article based on the available evidence; submitting the article online; making amendments as per the comments from referees; writing the CPD questions.
TH provided expert opinion on the medical problem and contributed to the literature search and writing up of the article based on the available evidence.