These lesions are congenital cholesteatomas of the CPA.The main MRI feature is diffusion restriction. These lesions severely restrict diffusion and do not enhance (Fig.5.17). Except for diffusion restriction, they show similar signal characteristics with CSF as arachnoid cysts [40].

Glomus tumors arising from the paraganglionic cells present as vascular lesions within the jugular foramen or ME.Temporal glomus tumors arise from the paragan­glia of Jacobson’s nerve, glossopharyngeal nerve (tympanic branch), or the Arnold’s nerve which is the branch of the vagus nerve. Glomus tympanicum tumors refers to those conned to the tympanic cavity (arising from Jacobson’s nerve) and those involving the jugular glomus, jugular bulb, and skull base (arising from Jacobson’s or Arnold’s nerve). The glomus jugulotympanicum has components in both the typanicum cavity and the jugular foramen. A blue reex behind the TM is an impor­tant clue for diagnosis. Patients usually complain of hearing loss and pulsatile tin­nitus [5]. CT scans show a highly vascular mass with a “salt-and-pepper” appearance due to intralesional calcications. MRI is invaluable in dening tumor extent, vas­cular supply, and relationship with critical structures. Dynamic contrast-enhanced MRI highlights the vascularity of the tumor (Fig.5.18). A glomus tumor should be

Squamous cell carcinoma (SCC), adenoid cystic carcinoma, basal cell carcinoma, and malignant melanoma may be seen in this region of the temporal bone. SCC of the external auditory canal is usually seen in senile patients, and radiologic ndings may resemble those of necrotizing external otitis (Fig.5.19). A differential diagno­sis can be made clinically with external otitis, with clinical noise and slow develop­ment of SCC [42].

Nonspecic symptoms common to infectious and inammatory diseases, such as facial paralysis and hearing loss, are seen in temporal bone tumors, making imaging extremely important. Although rare, temporal bone tumors require comprehensive radiologic evaluation for accurate diagnosis and optimal patient management. CT and MRI provide insights into the location, extent, vascularity, and tissue character­istics of these tumors, guiding therapeutic decisions and improving patient out­comes. With continued advances in imaging technology and collaboration between radiologists and clinical specialists, accurate identication and characterization of temporal bone tumors will continue to improve, enhancing our ability to provide tailored treatment approaches.

Congenital ME anomalies are usually sporadic and less common than external audi­tory canal dysplasia. Patients present with nonprogressive conductive hearing loss. CT must be used to evaluate the ossicles and facial nerves (Fig.5.22).

This is the most severe form of inner ear malformation in which the cochlea, vesti­bule, and SCCs are not formed. The cochlear and VAs are also absent. The outer and middle ear may be completely normal [46].

CT and MRI show a single cavity encompassing the cochlea and vestibule, often accompanied by a short cochlear nerve. Audiologic and imaging evaluations guide the management strategy, including consideration of cochlear implantation. The cochlea, vestibule, and SCC structures are indistinguishable (Fig.5.24) [46].

Otospongiosis/otosclerosis, is a common cause of mixed hearing loss and has a radiologic differential diagnosis with many diseases. It is benecial to share the patient’s clinical information with the radiology department so that the patient can receive an accurate diagnosis. Thin-slice HRCT is essential for both otosclerosis and pathologic third window. One should be aware of subtle radiographic ndings in otosclerosis and remember that there is a reason for pathologic third window.

Otosclerosis is a disease that progresses with abnormal bone remodeling [15,

52–54]. While demineralization is seen around the oval window in the early stages

In otosclerosis, imaging is used to conrm the clinical diagnosis and/or exclude diseases with similar clinical features. HRCT is a rst-line imaging modality. The thinnest technically possible axial slices should be obtained (0.5 or 0.625), and cor­onal and sagittal oblique reconstructions should be performed; this imaging tech­nique allows detection of subtle demineralization [1, 52, 55]. In addition, image quality should allow evaluation of the oval window, stapes footplate, and round window niche.

The current most widely used method for CT grading was proposed by Marshall etal. [56], and the grading system has excellent intra- and interobserver agreement [57]. Grade 1 is fenestral involvement only, and the involvement may be sclerotic or spongiotic. Grade 2 involves the cochlea, 2A involves the basal turn, and 2B involves the cochlea outside the basal turn. If the entire cochlea is involved, the lesion is grade 2C. Lesions have a patchy hyperdense appearance. In grade 2, cochlear involvement may or may not be associated with fenestral involvement. Grade 3 is