Third Window Lesions

Beyond Tympanomastoidectomy: A Review of Less Common Postoperative Temporal Bone CT Findings

“…More commonly, the transmastoid approach is used, in which a canal wall-up mastoidectomy is performed, the 3 semicircular canals are exenterated, and the vestibule is cleaned of neuroepithelium. 12,13 Surgical labyrinthectomy for any indication may lead to labyrinthitis ossificans and, much less commonly, CSF leak or facial nerve injury. In patients with surgical labyrinthectomy, air in the labyrinth is considered an expected finding; therefore, these cases should not be mistaken for traumatic or other acquired causes of perilymph fistula or pneumolabyrinth (Fig 4).…”

“…Clinically, a third window phenomenon is characterized by various signs such autophony (ie, prominently hearing one's own voice in the affected ear), sound-or pressure-induced vertigo and/or nystagmus (Tullio phenomenon and the Hennerbert sign, respectively), pulsatile tinnitus, and low-frequency conductive hearing loss with negative bone-conduction thresholds. 13,14 The diagnosis of SSCD can be suggested on heavily T2-weighted MR images but is best made on high-resolution axial and oblique reformatted CT views. On the Pöschl view (ie, images reformatted perpendicular to the long axis of petrous bone), SSCD is characterized by an absent or thinned-out osseous covering overlying the superior semicircular canal (SSC).…”

“…Defects in the LSC are more likely due to erosion secondary to infectious, inflammatory, or neoplastic conditions. 13 Very rarely, a radiologist may encounter a patient who underwent a remote LSC fenestration for otosclerosis. In LSC fenestration, an opening is made in the lateral semicircular canal through the mastoid; imaging findings can be mistaken for lateral semicircular canal dehiscence or LSC fistula if one is not aware of this procedure (Fig 7).…”

“…Raised intracranial pressure can also lead to CSF leaks. 13 Surgical approaches for skull base dehiscence repairs include transmastoid and MCF approaches. The transmastoid approach is preferred for smaller defects and defects within the tegmen mastoideum, while the MCF approach is used for defects that are larger, multiple, or in the tegmen epitympanum or petrous apex.…”

The Forgotten Second Window: A Pictorial Review of Round Window Pathologies

“…Third-window lesions refer to any range of pathology that creates an abnormal connection between the inner ear and either the middle ear or the intracranial cavity. 51 Acoustic energy is lost through these windows, often causing a so-called "pseudoconductive" hearing loss, which manifests as increased bone and decreased air conduction. 3,52 There are many such connections: vestibular aqueduct enlargement, semicircular canal dehiscence, and any other type of osseous thinning between the inner ear and adjacent vascular or nervous channels.…”