Diagnosis: Intracranial Hypertension
We have discussed various causes of pulsatile tinnitus in a few Clinical Consultation articles in the past. The importance of discussing this condition is related to understanding its workup and recognizing uncommon but potentially problematic causes. Generally, the first step is to obtain an MRI of the internal auditory canal (IAC) with and without gadolinium to rule out glomus jugulare or other tumors around the temporal bone. If the MRI is normal, the next step is magnetic resonance venography (MRV), which images the venous system intracranially. Most patients with pulsatile tinnitus report that they can suppress the sound by placing gentle pressure on their neck or by turning their head to one direction. This indicates a venous origin of the sound. Pulsatile tinnitus of arterial origin is uncommon, but when present, is usually not affected by maneuvers that suppress venous pulsatile tinnitus.
In this patient, the MRI of the IAC showed some interesting findings. First, the patient had an expanded empty sella (Fig. 2). The sella is a portion of the sphenoid bone that houses the pituitary gland. When there is an increase in intracranial pressure, the pituitary gland is squeezed to the bottom or posterior of the sella, creating an appearance that the sella does not contain the pituitary gland. Chronically increased pressure causes the sella to expand. The second finding on the MRI was the bilateral expansion of the patient's Meckel's cave (Fig. 3). Meckel's cave is an intradural space at the apex of the temporal bone that acts as a conduit for the trigeminal nerve between the pons and the cavernous sinus, and houses the trigeminal ganglion and the rootlets of the trigeminal nerve. Expansion of Meckel's cave occurs because of intracranial hypertension, and gradually erodes the temporal bone and petrous apex.
The patient had a normal MRI, but the MRV showed a sigmoid sinus diverticulum as well (Fig. 4). The CT of temporal bones showed a suspected meningocele (outpouching of the dura into the temporal bone) above the malleus (Fig. 5). All imaging findings pointed to intracranial hypertension (IH).
IH, previously called pseudotumor cerebri or benign intra-cranial hypertension, indicates an increased cerebrospinal fluid (CSF) pressure inside the skull. The term “benign” should not be used to refer to this condition since it can cause permanent problems for the patient and requires treatment. Most common symptoms are severe headaches (worse in the morning or with coughing or bending), pulsatile tinnitus, and visual disturbances. The mechanism for increased CSF pressure is not always clear, but it may be any combination of increased CSF production, decreased CSF drainage or absorption, or increased volume of brain tissue.
IH can be either primary or secondary. Primary IH, also called idiopathic IH (IIH), is IH without any known cause or inciting factor. It is most commonly seen in young, overweight women (a 9:1 female to male ratio) between 20 and 45 years old. In the United States, the incidence of primary IH is about 0.9 per 100,000 individuals (about 3.5 per 100,000 for women), increasing with higher obesity rates. Primary IH does affect men and children; however, it is much rarer and usually not associated with obesity.
Secondary IH has an identifiable cause such as head trauma, stroke, medications, infections, autoimmune conditions, sleep apnea, or liver or kidney failure. Because IH can be related to decreased drainage of CSF or increased brain tissue mass, it is critical to rule out mass-occupying lesions in the skull via MRI or CT in patients who present with symptoms suggestive of IH.
The increased intracranial pressure may compress the cranial nerves and cause optic nerve swelling, also known as papilledema. Compression of the cranial nerves may result in vision problems (due to compression of the third, fourth, and sixth cranial nerves) or facial numbness (due to compression of the fifth cranial nerve). Papilledema (edema of the retina around the optic nerve) may also cause visual disturbances, but not all patients exhibit symptoms. Long-standing papilledema can eventually cause optic nerve atrophy and permanent vision loss.
Many patients with IIH develop pulsatile tinnitus, usually described as a whooshing noise in the ears that is synchronous with the pulse. It may occur more on one side. It is important to ask patients what the tinnitus sounds like and whether it is synchronous with their pulse. An examination via auscultation of the neck and mastoid can help evaluate for carotid stenosis. Other symptoms experienced by IIH patients include pain in the neck or shoulder area, pain behind the eyes, and problems with moving or talking.
A full neurological exam is important for identifying the signs these patients may present with. If you suspect IH based on a patient's medical history or exam, a lumbar puncture or neuroimaging can be done to diagnose the condition. In cases of IIH, neuroimaging, including MRI, may have normal results or show subtle changes such as an empty sella, Meckel's cave diverticula, small ventricles, venous sinus stenosis, meningoceles protruding into the temporal bone or sinuses, cerebellar tonsillar ectopia (mimicking Chiari malformation), globe flattening, and optic nerve head protrusion. Certain causes of secondary IH may also be visible on MRI or be elucidated through abnormal lab results. Because imaging can sometimes appear normal, a lumbar puncture can also be used to identify increased CSF pressure (>25cm H2O).
Secondary causes include head trauma, stroke, dural venous thrombosis, and medications or substances (e.g., vitamin A, tetracyclines, isotretinoin, amiodarone, nitrofurantoin, lithium, and hormonal contraceptives). Some infections such as meningitis, HIV, Lyme disease, poliomyelitis, malaria, and syphilis, as well as systemic illnesses, (e.g., lupus, Behçet's disease, Addison's disease, sleep apnea, liver failure, and kidney failure) can also cause IH.
For treatment, all patients with obesity are advised to lose weight. For patients who are symptomatic but without immediate threat to vision, medications such as acetazolamide, which block the production of CSF, are often used.
For patients with imminent threat to vision (declining visual function within four weeks of diagnosis), surgical management such as optic nerve sheath fenestration, neurovascular stenting, or a CSF shunt is recommended.
BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS
Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.
- Video 1. Axial (horizontal) CISS showing the full extent of the Meckel's cave diverticula.
- Video 2. Axial (horizontal) T2 showing small ventricles, indicating that the patient is likely suffering from intracranial hypertension.
- Video 3. Sagittal (parallel to auricle) T2 FLAIR MRI showing an empty sella.
- Video 4. Four-vessel MRA showing no aneurysm.
- Video 5. MRV showing the left sigmoid sinus diverticulum and no other venous sinus stenosis.
- Video 6. Axial CT of the left temporal bone showing the soft tissue and fluid in the middle ear and mastoid.
Watch the patient videos online at thehearingjournal.com https://journals.lww.com/thehearingjournal/Pages/collectiondetails.aspx?TopicalCollectionId=23.Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.