Temporal Encephalocele: Causes, Epilepsy, and Surgery

A temporal encephalocele is a herniation of brain tissue, with or without its surrounding membranes, through a defect in the bone that forms the floor of the middle cranial fossa. The temporal bone sits just above the ear, and when it develops a gap or thins enough to give way, brain tissue can push through into the middle ear space or the mastoid bone behind it. This condition can cause cerebrospinal fluid leaks, hearing loss, seizures, and in serious cases, life-threatening meningitis. Despite those risks, temporal encephaloceles are frequently missed or mistaken for common ear problems, sometimes for years before the real diagnosis emerges.

What Causes a Temporal Encephalocele

Temporal encephaloceles fall into two broad categories: congenital and acquired. Congenital cases involve skull base defects present from birth, while acquired cases develop later in life from trauma, prior ear surgery, chronic ear disease, or, increasingly recognized, elevated pressure inside the skull. Reporting of both cerebrospinal fluid (CSF) leaks and temporal encephaloceles has risen over the past decade, partly because imaging has improved and partly because clinicians are more aware of the condition.¹

One factor that keeps coming up in the literature is idiopathic intracranial hypertension (IIH), a condition in which the pressure of the fluid surrounding the brain is chronically elevated for no obvious structural reason. A study measuring intracranial pressure in patients with spontaneous encephaloceles and CSF leaks found that roughly two-thirds had elevated pressure, while only about a third had normal readings. The researchers noted that the rate of elevated intracranial pressure in these patients far exceeded its rate in the general population and recommended that everyone presenting with a spontaneous encephalocele be evaluated for it.² A separate institutional review from the University of Pennsylvania reinforced this connection, describing spontaneous temporal encephaloceles as an increasingly recognized consequence of IIH and noting that elevated intracranial pressure complicates surgical management and raises the risk of recurrence.³

Prior ear surgery is another well-known trigger. A canal wall down mastoidectomy, a procedure used to treat cholesteatoma (an abnormal skin growth in the middle ear), can weaken the bony floor of the middle cranial fossa enough that brain tissue eventually herniates through it.⁴ Trauma, including head injuries that fracture the temporal bone, rounds out the list of acquired causes.

How Temporal Encephaloceles Present

The symptoms depend on where and how far the brain tissue has pushed through. The most common presentations revolve around the ear: fluid draining from the ear canal (CSF otorrhea), hearing loss, and a persistent sense of ear fullness. In a case series of 34 patients with temporal encephaloceles and CSF leaks, CSF otorrhea was present in about 56% of cases, and nearly 15% of patients had already experienced meningitis before surgery.⁵ Another review noted that at the time of diagnosis, confirmed CSF leak was present in most patients, with hearing loss and ear fullness being additional common complaints. More serious complications included meningitis and, in one case, neurological deficits from a venous infarction.⁶

The hearing loss is usually conductive, meaning it results from the encephalocele physically obstructing sound transmission through the middle ear rather than from nerve damage. In a series of eight patients with CSF leaks and middle cranial fossa encephaloceles, all had defects in the tegmen tympani (the thin bony plate forming the roof of the middle ear), and conductive hearing loss was a shared finding.⁷

Bilateral cases are uncommon but do occur. One report described a 54-year-old man with spontaneous tegmen defects on both sides who presented with severe meningitis, underscoring that the condition can be more extensive than a single defect on one side.⁸

Temporal Encephaloceles and Epilepsy

Beyond the ear-related symptoms, temporal encephaloceles have become an increasingly recognized cause of drug-resistant epilepsy. The herniated brain tissue can become a seizure focus, and because the encephalocele itself is often subtle on imaging, the connection to epilepsy can go unrecognized for years. A review of imaging in temporal lobe encephalocele-associated epilepsy noted that these herniations are frequently underdiagnosed in epilepsy patients due to their subtle appearance and their location in the middle cranial fossa.⁹

Case reports illustrate just how elusive the diagnosis can be. Two adult patients with epilepsy linked to temporal encephaloceles were described: a 28-year-old woman whose right temporal encephalocele was missed on initial neuroimaging, and a 43-year-old woman whose left temporal encephalocele was only discovered during surgery after being misdiagnosed as a tumor.¹⁰

The good news is that when the encephalocele is identified and surgically treated, seizure outcomes are often favorable. A systematic review and meta-analysis pooling data from 13 studies found that about 65% of patients with drug-resistant epilepsy achieved seizure freedom after resection, and roughly 78% had a favorable seizure outcome overall.¹¹ A single-center case series showed even more striking results: among patients who underwent resection of the anterior temporal pole, the seizure freedom rate was about 88%, while none of the patients managed without surgery achieved seizure freedom.¹² That contrast highlights why finding the encephalocele matters so much: it can be the difference between a surgically curable seizure disorder and years of ineffective medication changes.

Why the Diagnosis Is So Often Delayed

One of the most frustrating aspects of temporal encephaloceles is how long patients can go without a correct diagnosis. The symptoms overlap heavily with common middle ear conditions, and CSF draining into the ear can easily be mistaken for the fluid buildup seen in serous otitis media (fluid behind the eardrum) or chronic ear infections. A study of the clinical spectrum of spontaneous encephaloceles found that all but two patients in the series had initially been misdiagnosed with serous or chronic otitis media, with the average delay before correct diagnosis running about 1.6 years and the longest delay stretching to a full decade.¹³

Part of the problem is that standard treatments for middle ear fluid, like placing ear tubes (myringotomy with tympanostomy tubes), can actually make things worse if the underlying problem is a CSF leak. In one series, over 40% of patients had already undergone tube placement before the encephalocele was identified.¹⁴ Creating a hole in the eardrum when the fluid behind it is spinal fluid opens a direct path from the brain to the outside world, raising the risk of meningitis. This is one reason clinicians who evaluate persistent, unexplained middle ear effusions in adults are increasingly urged to consider temporal bone defects with CSF leak in their thinking.

Imaging and Diagnosis

Diagnosing a temporal encephalocele relies on imaging, but the choice of modality matters a great deal. High-resolution CT of the temporal bones is the go-to first step and excels at showing bony defects in the tegmen, the thin plate of bone separating the middle ear and mastoid from the brain. However, CT alone can miss encephaloceles that have not yet caused a visible bony gap, or small herniations that do not clearly stand out against surrounding soft tissue. A study directly comparing the two main modalities found that CT had a sensitivity of only about 17% for detecting temporal bone encephaloceles, while MRI reached roughly 58%. Both had perfect specificity, meaning that when either scan showed an encephalocele, it was truly there, but CT missed the majority of cases.¹⁵

In practice, most specialists now recommend combining the two: CT to assess the integrity of the bony skull base and MRI to look for the soft-tissue herniation itself. For patients with a history of cholesteatoma, where the concern is distinguishing a recurrent cholesteatoma from an encephalocele, a combination of high-resolution temporal bone CT and specialized diffusion-weighted MRI has been recommended.¹⁶ The bottom line is that relying on CT alone will miss many cases; MRI adds meaningful diagnostic value, especially in the setting of epilepsy or when CSF leak is suspected but CT looks normal.

Surgical Approaches

Once a temporal encephalocele is confirmed and symptomatic, surgery is the standard treatment. The goal is to reduce the herniated brain tissue back into the cranial cavity, repair the dural defect (the hole in the membrane lining the brain), and reconstruct the bony floor to prevent recurrence. Three main surgical routes exist, and the choice depends on the size and location of the defect, the number of defects, and the surgeon’s experience.

The transmastoid approach goes through the bone behind the ear. It avoids the need to lift or retract the brain and is generally considered less invasive. For appropriately selected patients, this approach provides stable repair without the risks associated with brain retraction.¹⁷ A review of 31 consecutive cases using this route found that the defect involved the middle fossa floor in 90% of cases, and multiple defects were present in about a fifth of patients.¹⁸

The middle cranial fossa (MCF) approach involves a craniotomy, providing direct visualization of the skull base floor from above. This is often preferred for large defects, defects in locations that are hard to reach from below, or cases with multiple holes. A combined mastoid-middle fossa approach merges the two, and a large series found it was used in about 64% of operations. When the repair used a multilayer technique with the patient’s own tissue (autologous grafts), the success rate was high: over 96% of patients had neither recurrent CSF leak nor meningitis at follow-up after excluding cases where titanium mesh was used.¹⁹

Cost is a practical consideration, too. A comparison of billing costs and outcomes found that the transmastoid approach is an effective and less expensive alternative to the MCF approach for well-selected patients with otogenic CSF leaks and encephaloceles.²⁰ The decision is not one-size-fits-all: smaller, single-site defects are often good candidates for the transmastoid route, while larger or multifocal defects tend to steer surgeons toward the MCF or combined approach.

Reconstruction Materials

What surgeons use to patch the defect matters almost as much as the approach. The traditional technique layers the patient’s own tissue, typically fascia (the tough connective tissue covering muscle), sometimes combined with cartilage or bone grafts. One case report detailed an intracranial repair using temporalis fascia, nasal septum cartilage, and an artificial dural graft arranged in layers from inside the brain cavity outward.²¹

Newer synthetic and semi-synthetic materials have entered the picture. A study evaluating a fibrin glue-coated collagen patch for dural repair during temporal bone CSF leak and encephalocele surgery found that it produced results comparable to other materials, including autologous fascia and other commercially available collagen products, while potentially being more cost-effective.²² The general takeaway from the surgical literature is that multilayer repair, whether using autologous tissue, synthetic grafts, or a combination, produces durable results. The specific materials matter less than the principle of creating a robust, watertight seal across the defect.

Recurrence and the Role of Intracranial Pressure

Even after a technically successful repair, temporal encephaloceles can come back. The recurrence rate across large series hovers in the single digits, but it is not zero, and certain patients are at substantially higher risk. The most important predictor of recurrence is untreated elevated intracranial pressure. If the same force that pushed brain tissue through the skull base in the first place is still present after surgery, the repair is working against ongoing hydraulic pressure from above.

This is why many surgical teams now routinely measure intracranial pressure in patients with spontaneous temporal encephaloceles. In cases where pressure is elevated, some patients undergo placement of a ventriculoperitoneal (VP) shunt, which diverts excess cerebrospinal fluid to the abdominal cavity and relieves the pressure on the repair.²³ Weight management is also part of the conversation, since obesity is a known risk factor for IIH. Addressing intracranial pressure is not optional follow-up care; it is an essential component of preventing the whole problem from recurring.

Temporal Encephaloceles in Children

Most of the literature on temporal encephaloceles involves adults, but the condition does occur in children and has its own distinct features. A study evaluating childhood-onset drug-resistant temporal lobe epilepsy due to encephaloceles included 11 children with a median age of epilepsy onset of 11 years. Strikingly, none had a history of head trauma, which is a commonly cited risk factor in adults. About a third had a body mass index above the 85th percentile for their age and sex, suggesting that the link between elevated weight and intracranial pressure may be relevant even in young patients. No child in that series had bilateral encephaloceles.²⁴

The diagnostic delay was notable here as well: the median time between epilepsy diagnosis and detection of the encephalocele was three years, with the longest gap stretching to 13 years. In over a third of cases, the encephalocele was only identified when imaging was re-reviewed at an epilepsy surgery conference. All the herniations in these children were “contained” defects without visible bone gaps, which helps explain why they were so easy to miss on standard imaging. For any child with unexplained drug-resistant temporal lobe epilepsy and no clear cause on initial scans, a careful second look for subtle encephaloceles is warranted.

What Happens to the Herniated Brain Tissue

A reasonable question for anyone learning about temporal encephaloceles is whether the brain tissue that has pushed through the skull base is still functional. In most cases, the herniated tissue has been chronically compressed and distorted enough that it is no longer contributing meaningfully to normal brain function. Surgical reports generally note that removing or reducing the herniated tissue does not cause new neurological deficits.²⁵ In the context of epilepsy surgery, the herniated tissue is often the seizure focus itself, so resecting it serves the dual purpose of sealing the defect and eliminating the source of seizures. This is part of why surgical outcomes for encephalocele-associated epilepsy tend to be better than many other forms of drug-resistant epilepsy: when you remove the abnormal tissue and repair the structural problem, you are addressing the root cause rather than managing downstream symptoms.

For patients whose encephalocele presents primarily with CSF leak or hearing problems rather than seizures, the surgical priority shifts to sealing the defect and preventing meningitis. The herniated tissue is reduced back into the cranial cavity when possible, and the bony and dural layers are reconstructed. Hearing outcomes after repair vary: conductive hearing loss caused by the mass in the middle ear often improves, but the degree of recovery depends on how much damage the middle ear structures sustained before surgery and whether the repair itself alters the anatomy of the sound-conducting chain.