Topographic Approach to Differential Diagnosis: Approach to External Ear Pathologies
摘要
The pinna is easily examined clinically, so imaging has a limited role, but CT and MRI are useful for evaluating the extent of lesions and associated abnormalities of the middle ear, skull base, or mastoid. High-resolution CT of the temporal bone with additional soft tissue and 3D reconstructions is the primary imaging modality, while MRI is used as a problem-solving tool in selected cases. Conditions affecting the pinna include congenital anomalies such as microtia and anotia, which are frequently associated with external auditory canal (EAC) and middle ear abnormalities and may occur as part of syndromic conditions. Preauricular sinus arises from incomplete fusion of auricular hillocks and is usually a benign entity, although infection may occur, with ultrasound being most useful for evaluation. First branchial cleft anomalies are rare and may present as cysts, sinuses, or fistulas near the EAC, often closely related to the parotid gland and facial nerve. Mass lesions of the pinna are most commonly benign skin or adnexal lesions, though malignant tumors such as squamous cell carcinoma and basal cell carcinoma can also occur. Calcification of the elastic cartilage of the pinna may be seen in systemic conditions such as diabetes mellitus, gout, relapsing polychondritis, or following trauma. Pathologies affecting the EAC include congenital or acquired stenosis, diffuse inflammatory wall thickening, and infections such as otitis externa, necrotizing otitis externa, and herpes zoster oticus. Focal soft tissue masses in the EAC have a broad differential diagnosis including cerumen, medial canal fibrosis, cholesteatoma, keratosis obturans, cholesterol granuloma, benign tumors, and malignancy, with HRCT and MRI providing important diagnostic clues. Other EAC conditions include foreign bodies, commonly seen in children, and fractures due to trauma, which are best evaluated using dedicated CT reconstructions.