Congenital cholesteatoma

• Well-defined round or oval soft-tissue mass in the anterosuperior middle ear near the tensor tympani, behind an intact tympanic membrane
• Marked hyperintensity on high-b-value non-EPI diffusion-weighted imaging with corresponding low ADC, distinguishing cholesteatoma from simple fluid
• Bone erosion involving the long process of incus or stapes, or extension into epitympanum, facial recess, sinus tympani, or mastoid

• On high-resolution CT: small, relatively well-defined round or oval soft-tissue mass; larger lesions may be irregular; assess ossicular contact or erosion, particularly the long process of incus and stapes; evaluate epitympanic, facial recess, sinus tympani, and mastoid extension; petrous lesions appear as sharply defined lytic lesions with soft-tissue density.
• On MRI T1/T2: usually low-to-intermediate T1 signal and relatively high T2 signal; the lesion itself generally does not enhance; T2 signal may be lower than adjacent fluid or inflammatory change.
• Non-EPI diffusion-weighted imaging is the preferred sequence for characterization: typically conspicuously bright on high-b-value DWI with corresponding low ADC; lesions around 2 mm can sometimes be detected; non-EPI DWI is less susceptible to temporal-bone distortion than conventional EPI DWI.
• Location: characteristically begins in the anterosuperior middle ear near the tensor tympani tendon, then may extend posteriorly toward the incudostapedial joint, superiorly into the epitympanum, and eventually into the mastoid.
• Critical imaging distinction from acquired cholesteatoma: congenital disease presents with an intact tympanic membrane and no history of perforation or prior otologic surgery; pars flaccida acquired disease shows retraction pocket and Prussak's space involvement, while pars tensa acquired disease typically arises posteriorly in sinus tympani/facial recess.
• Petrous bone lesions (less common) may present later with mixed hearing loss or facial nerve dysfunction and present as sharply defined lytic lesions; warrant particular attention to cochlear and semicircular-canal erosion.
• The absence of bone erosion on CT does not exclude early congenital cholesteatoma, as small lesions may not yet cause osseous changes.
• Preoperative reporting must specify compartment and quadrant, maximal size, ossicular integrity, and involvement of epitympanum, facial recess, sinus tympani, mastoid, facial canal, labyrinth, tegmen, IAC, carotid canal, or jugular bulb.

• Acquired cholesteatoma: distinguished by history of perforation, prior surgery, or otoscopic findings of retraction pocket; pars flaccida type centers on Prussak's space with scutum blunting and early lateral ossicular involvement; pars tensa type arises posteriorly in sinus tympani/facial recess.
• Effusion, inflammatory tissue, or granulation: opacification without a discrete expansile mass or characteristic DWI hyperintensity favors inflammatory disease; granulation tissue enhances with contrast.
• Middle ear adenoma: soft-tissue mass that generally lacks characteristic diffusion restriction; often a diagnosis of exclusion on imaging.
• Tympanic paraganglioma: avidly enhancing vascular mass centered on the cochlear promontory, in contrast to the nonenhancing keratin lesion of cholesteatoma.
• Facial nerve schwannoma or venous vascular lesion: lesion tracks the facial nerve canal or enlarges the geniculate fossa with enhancement; venous lesions may show honeycomb-like osseous changes.
• Aberrant internal carotid artery or other vascular lesions: establish vascular course on imaging before any intervention to avoid surgical complication.
• Petrous apex cholesterol granuloma: bright on both T1 and T2 without the characteristic diffusion restriction of cholesteatoma; other petrous apex entities (cephalocele, mucocele, neoplasm) distinguished by anatomy, signal, enhancement, and diffusion properties.

For a characteristic preoperative case, report: "Discrete [location] middle ear mass measuring [size], demonstrating marked signal on non-EPI DWI, consistent with cholesteatoma. [Describe ossicular erosion and compartmental extension.] In the setting of an intact tympanic membrane and no relevant prior surgery or perforation, the location favors congenital cholesteatoma." This phrasing separates the imaging diagnosis from the clinical determination of origin.

• Assuming that absence of bone erosion on CT excludes congenital cholesteatoma: early-stage disease may not yet cause osseous changes despite being a true cholesteatoma, so small lesions with characteristic DWI signal should still raise suspicion.
• Confusing congenital and acquired cholesteatoma based on imaging alone: clinical history (intact tympanic membrane, no prior perforation or surgery) and otoscopy are mandatory to establish congenital origin; large lesions can be difficult to classify radiologically.
• Using conventional EPI diffusion-weighted imaging for temporal-bone evaluation: non-EPI DWI is strongly preferred as it is less susceptible to metal artifact and distortion, particularly for small lesions in the middle ear.
• Misinterpreting a vascular lesion (aberrant carotid artery, paraganglioma, facial nerve schwannoma) as cholesteatoma: careful evaluation of enhancement pattern, location, and vascular relationships on CT and MRI is essential before surgical planning.
• Relying solely on CT attenuation to characterize middle ear soft-tissue disease: DWI characteristics are necessary to distinguish cholesteatoma from effusion, granulation, or other inflammatory entities that may have similar density on CT.