Idiopathic Intracranial Hypertension (IIH) is an elevation of intracranial pressure (ICP) without a clear etiology, diagnosed by the modified Dandy criteria. The prevalence of IIH is increasing, rising sharply from 12 to 76 per 100,000 between 2003 and 2017. The incidence has also increased from 2.3 to 7.8 per 100,000, with over 90% of patients being obese (BMI > 30 kg/m²). Women account for 92.1% of IIH cases, and a prevalence of 3.44 per 10,000 (95% CI: 2.61–5.39) has been reported among women aged 18–552).
Tegmen is a bony plate forming the boundary between the middle cranial fossa and the middle ear/mastoid cavity, consisting of two parts: the tegmen tympani and the tegmen mastoideum. Because it is a thin, pneumatized bone that is structurally fragile, prolonged exposure to hydrostatic pressure from elevated ICP leads to gradual thinning (attenuation).
Progressive thinning eventually leads to dehiscence (bone defect). The main complications resulting from dehiscence are as follows:
Handzel et al. demonstrated that tegmen tympani defects in IIH patients are not congenital but rather an acquired condition associated with elevated ICP. Obesity and high BMI are common risk factors for both IIH and tegmen thinning/defects.
When elevated ICP due to IIH erodes the tegmen tympani and creates a fissure, cerebrospinal fluid leaks into the middle ear cavity. This CSF leak itself lowers ICP, paradoxically leading to intracranial hypotension symptoms including orthostatic headache.
In the stage of tegmen tympani thinning, patients are usually asymptomatic, and symptoms appear only after a fissure develops.
Intracranial hypotension symptoms after CSF leak:
Symptoms of IIH itself (may be present before fissure formation):
The modified Dandy criteria used for the diagnosis of IIH are shown below (Cao 20251)).
| Item | Criteria |
|---|---|
| Symptoms | Signs and symptoms of elevated ICP (papilledema, headache, nausea, vomiting) |
| Neurological findings | No neurological abnormalities other than cranial nerve palsy |
| Neuroimaging | Normal brain parenchyma (no hydrocephalus, no mass) |
| Cerebrospinal fluid composition | Normal |
| Lumbar puncture opening pressure | ≥250 mm H₂O (adults), ≥280 mm H₂O (children) |
The exact etiology of tegmen tympani thinning and dehiscence is not established, but several risk factors have been identified.
Major risk factors for IIH:
Vitamin D deficiency has also been reported as a cause of secondary pseudotumor cerebri (IIH-like disease) 3).
In cases where the tegmen tympani is thinned due to IIH, it has been reported that rapid pressure changes (barotrauma) during air travel can induce acute rupture of the tegmen tympani 1). There is a case where a right tegmen tympani fissure developed after eight consecutive flights over eight months. It is recommended to consult with your doctor.
High-Resolution CT (HRCT)
Role: Gold standard for detecting tegmen tympani defects1).
Accuracy: Sensitivity 92%, specificity 93%.
Imaging conditions: Thin-slice coronal and axial scans accurately depict bone defects, meningocele herniation, and fistulas.
MRI (T2/Cisternography)
Role: Complements HRCT.
Usefulness: Useful for identifying CSF leakage and soft tissue abnormalities (meningoencephalocele). Also useful for evaluating findings supporting IIH (transverse sinus stenosis, empty sella, optic nerve sheath enlargement) 1).
MRV (MR Venography)
Role: Evaluation of transverse sinus stenosis. It is a supportive finding for IIH and contributes to determining treatment strategy 1).
Surgical closure is recommended for symptomatic tegmen tympani dehiscence (to prevent infection and brain herniation). The following three surgical approaches are available.
In Cao case 2, transmastoid approach and tympanoplasty were performed, resulting in improved hearing and complete closure of the air-bone gap postoperatively1). In contrast, for Cao case 1, observation with tympanostomy tube placement was chosen1).
Important note: After surgical closure of tegmen tympani dehiscence, ICP may increase and IIH symptoms may recur1). This is because the reduction in ICP due to CSF leakage is resolved postoperatively. Fundamental ICP management (weight control, medication) is essential.
No. Surgical closure of the tegmen tympani defect is important to prevent CSF leak, infection, and brain herniation, but it is not a treatment for IIH itself. After closure, ICP elevation may recur and IIH symptoms may worsen, so fundamental ICP management such as weight control and medication must be performed concurrently 1).
At the skull base, hydrostatic pressure associated with elevated ICP erodes the tegmen, eventually leading to dehiscence and CSF leakage. Multiple studies have shown that this process is progressive.
Handzel et al. measured the vertical distance between the middle cranial fossa floor and anatomical landmarks on serial CT scans and found a significant correlation between LP opening pressure and the degree of tegmen thinning 1).
Rabbani et al. measured the thickness of the cranial vault, zygomatic bone, and skull base on high-resolution CT and reported that intracranial hypertension is independently associated with thinning of the cranial bones 1). Patients with intracranial hypertension had significantly thinner cranial vault and skull base compared to controls.
Berkiten et al. reported that in patients with IIH, the bony roof of the superior semicircular canal was significantly thinner and the incidence of superior semicircular canal dehiscence (SSCD) was higher 1). This suggests that bone thinning occurs not only in the tegmen but throughout the skull base.
The relationship between intracranial pressure and intracranial volume is described by an S-shaped pressure-volume curve. Within a volume increase of 30 cm³, ICP changes are minimal, but when compensatory mechanisms are exhausted, ICP rises sharply. ICP elevation occurs due to space-occupying lesions, CSF pathway obstruction, venous sinus stenosis, etc., and involves disturbances in CSF dynamics regulation, metabolic, and hormonal factors. The involvement of the glial-neuro-vascular interface has also been suggested.
This is because chronic ICP elevation causes hydrostatic pressure to erode skull base bones such as the tegmen tympani. In a consecutive CT study by Handzel et al., a significant correlation was found between lumbar puncture opening pressure and the degree of tegmen tympani thinning1), confirming that this thinning is not congenital but an acquired change associated with ICP elevation.
Cao et al. (2025) reported the first two cases of barotrauma-induced tegmen tympani dehiscence in patients with IIH1). Case 1 (59-year-old female, BMI 38.3) presented with right ear fullness and ear pain after 8 consecutive flights over 8 months; CT revealed right tegmen tympani dehiscence and a small meningocele. Tympanostomy tube placement and observation were chosen (acetazolamide was declined). Case 2 (65-year-old female, BMI 32.1) presented with otorrhea, ear pain, and hearing loss after 7 months of CPAP use; CT showed left mastoid tegmen dehiscence and meningoencephalocele. Transmastoid approach and tympanoplasty improved postoperative hearing. This report highlights the importance of raising awareness of barotrauma risk and preventive counseling in IIH patients.
Fraz et al. (2025) reported the prevalence of IIH among women aged 18–55 years as 3.44 per 10,000 in a US national survey, and found a significant geographic correlation where states with higher obesity prevalence also had higher IIH prevalence 2). An increase in the number of IIH patients also means an increase in the number of cases with tegmen tympani complications.
