Tegmen Attenuation and Dehiscence in Idiopathic Intracranial Hypertension (IIH)
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Disease Entity
Disease
Idiopathic intracranial hypertension (IIH) (i.e., pseudotumor cerebri) is a disorder characterized by signs and symptoms of elevated intracranial pressure (ICP) without a clear etiology[1] and the disorder is defined using the modified Dandy criteria (see EyeWiki on IIH).
The tegmen is the osseous plate that forms the border between the middle cranial fossa and the middle ear and mastoid cavity. The tegmen is a thin, pneumatized bone that is relatively structurally weaker than the rest of the skull base.
The tegmen can be separated into 2 parts: 1) The tegmen tympani, which is a bony plate that separates the middle ear from the middle cranial fossa 2) Tegmen mastoideum, which is a bony plate that separates the mastoid air cells from the middle cranial fossa.[2]
Tegmen attenuation is the thinning of the tegmen tympani and/or tegmen mastoideum bones.[3] Some authors theorize that the gradual thinning of the tegmen may eventually lead to dehiscence resulting in conductive hearing loss, meningoencephalocele, CSF leak, and otogenic meningitis.[3] Interestingly, elevated intracranial pressure (ICP) as in IIH can erode the thin tegmen and present with low ICP (intracranial hypotension). Thus, obesity and elevated body mass index (BMI) may be risk factors for both IIH and tegmen attenuation and dehiscence.[4]
Epidemiology
The prevalence of IIH (2003 to 2017) increased from 12/100,000 to 76/100,0004 and the incidence of IIH during the same period increased from 2.3/100,000 to 7.8/100,000.[5] Greater than 90% of patients with IIH are obese[5] (BMI > 30 kg/m2).[4] Between 1990 and 2014, Olmsted County identified 63 cases of IIH, with females constituting 92.1% of the diagnosed individuals.[6] Among these patients, 60.3% were obese and over half of that subset were morbidly obese (BMI > 40 kg/m2).[6] Among obese females aged 15-44, the incidence rate of IIH was 22/100,000 compared to 6.8/100,000 for all female patients of the same age.[6] Obesity may be a risk factor for tegmen dehiscence and IIH.[3] Handzel hypothesized that tegmen dehiscence is an acquired pathology associated with increased ICP rather than a congenital condition in patients with IIH.[3]
Etiology/Risk Factors
The precise etiology of tegmen attenuation and dehiscence remains ill defined. Transverse venous sinus stenosis, a common neuroimaging finding in IIH patients, may be an independent risk factor contributing to tegmen attenuation and spontaneous CSF leak.[7]
Pathophysiology
The presumed mechanism of tegmen dehiscence is elevated ICP related hydrostatic force at the skull base.3 Erosion of the tegmen and ultimately a dehiscence of the tegmen can lead to a CSF leak.
Diagnosis
Tegmen attenuation is typically asymptomatic until tegmen dehiscence occurs. Some cases of tegmen attenuation are discovered on routine imaging as an incidental finding (e.g., computed tomography (CT) scan of the temporal bone). When attenuation leads to dehiscence, signs and symptoms of a CSF leak may be present. Intracranial hypotension can cause blurred vision, diplopia (non-localizing sixth nerve palsy), nausea, vestibulocochlear symptoms, cognitive dysfunction, fatigue, and chronic subdural hematoma. The most common symptom is orthostatic headache (worse upon standing).[8] In cases where the tympanic membrane is perforated, CSF otorrhea may occur. CSF leak can increase the risk of otogenic meningitis.[9] The CSF leak may drain through the eustachian tube, resulting in a sensation of "post-nasal" drip.
Diagnostic Procedures
The thinning of the tegmen is typically visible on dedicated CT imaging of the internal auditory canal. CSF or brain tissue herniation may be seen on magnetic resonance imaging (MRI) in tegmen dehiscence. In cases of prior elevated ICP (e.g., IIH), the radiographic findings of IIH may be present including an empty sella turcica, optic nerve protrusion, distension of the optic nerve sheath, optic nerve tortuosity, posterior globe flattening, and transverse sinus stenosis.[10] Conversely, cranial MRI with contrast in patients with intracranial hypotension may show a full sella, subdural fluid collections, and pachymeningeal enhancement.
In the presence of a suspected CSF leak, beta-2 transferrin testing can confirm the presence of CSF rather than other fluids.[11] A CT scan showing thin or missing bone at the tegmen tympani and/or mastoideum can confirm tegmen attenuation and dehiscence and there may be an associated meningocele or meningoencephalocele on CT or MRI. A lumbar puncture can measure the ICP and also exclude meningitis in cases with symptoms or signs of increased (e.g., IIH) or decreased ICP (intracranial hypotension).
Management
Surgical closure is recommended in cases of symptomatic tegmen dehiscence to avert potential infections or additional herniation of brain parenchyma. Paradoxically, closure of the tegmen dehiscence and secondary CSF leak may lead to increased ICP and recurrence of symptoms and signs of IIH in some cases.
Prognosis
After surgical treatment of the tegmen dehiscence (e.g., transmastoid, middle fossa, or combined transmastoid-middle fossa approach) there is typically resolution of the CSF leak and improvement in symptoms. One study showed that surgical repair of tegmen defects using a middle fossa craniotomy approach with temporalis fascia autografts demonstrated safety and efficacy for successful long-term closure of dural defects.[9] After an average follow-up of 252 days following middle fossa approach, there was symptomatic improvement and the reduction of potentially severe consequences.
Summary
Tegmen attenuation and dehiscence may present with a CSF leak and symptoms and signs of low ICP. Interestingly, some of these cases of acute low ICP (CSF leak) may be the result of chronic high ICP (e.g., IIH) due to erosion of the tegmen over time. Clinicians should be aware that surgical closure of the tegmen dehiscence may result in recurrence of symptoms and signs of IIH.
References
- ↑ De Simone R, Sansone M, Curcio F, et al. Recurrent reflex syncope in idiopathic intracranial hypertension patient resolved after lumbar puncture: pathogenetic implications. BMC Neurol. 2023;23(1):416. Published 2023 Nov 21. doi:10.1186/s12883-023-03451-9
- ↑ Juliano AF, Ginat DT, Moonis G. Imaging review of the temporal bone: part I. Anatomy and inflammatory and neoplastic processes. Radiology. 2013;269(1):17-33. doi:10.1148/radiol.13120733
- ↑ 3.0 3.1 3.2 3.3 Handzel O, Brenner-Ullman A, Niry D, et al. Tegmen attenuation in patients with idiopathic intracranial hypertension is progressive. Laryngoscope. 2020;130(12):E904-E910. doi:10.1002/lary.28490
- ↑ 4.0 4.1 Subramaniam S, Fletcher WA. Obesity and Weight Loss in Idiopathic Intracranial Hypertension: A Narrative Review. J Neuroophthalmol. 2017;37(2):197-205. doi:10.1097/WNO.0000000000000448
- ↑ 5.0 5.1 Miah L, Strafford H, Fonferko-Shadrach B, et al. Incidence, Prevalence and Healthcare Outcomes in Idiopathic Intracranial Hypertension: A Population Study [published online ahead of print, 2021 Jan 20]. Neurology. 2021;96(8):e1251-e1261. doi:10.1212/WNL.0000000000011463
- ↑ 6.0 6.1 6.2 Kilgore KP, Lee MS, Leavitt JA, et al. Re-evaluating the Incidence of Idiopathic Intracranial Hypertension in an Era of Increasing Obesity. Ophthalmology. 2017;124(5):697-700. doi:10.1016/j.ophtha.2017.01.006
- ↑ Hurel C, Favier V, de Bonnecaze G, et al. Transverse Venous Sinus Stenosis in Patients With Nasal Cerebrospinal Fluid Leak and Idiopathic Intracranial Hypertension. Otolaryngol Head Neck Surg. 2023;169(6):1647-1653. doi:10.1002/ohn.414
- ↑ El Rahal A, Haupt B, Fung C, et al. Surgical closure of spinal cerebrospinal fluid leaks improves symptoms in patients with superficial siderosis. Eur J Neurol. Published online November 28, 2023. doi:10.1111/ene.16122
- ↑ 9.0 9.1 Braca JA 3rd, Marzo S, Prabhu VC. Cerebrospinal Fluid Leakage from Tegmen Tympani Defects Repaired via the Middle Cranial Fossa Approach. J Neurol Surg B Skull Base. 2013;74(2):103-107. doi:10.1055/s-0033-1333616
- ↑ Barkatullah AF, Leishangthem L, Moss HE. MRI findings as markers of idiopathic intracranial hypertension. Curr Opin Neurol. 2021;34(1):75-83. doi:10.1097/WCO.0000000000000885
- ↑ Haft GF, Mendoza SA, Weinstein SL, Nyunoya T, Smoker W. Use of beta-2-transferrin to diagnose CSF leakage following spinal surgery: a case report. Iowa Orthop J. 2004;24:115-118.
