Benign lymphoepithelial cyst: This is a common cause of a firm, fixed preauricular mass, often associated with HIV infection or other immunocompromised states. The cysts are usually painless and can be single or multiple.

Parotid gland tumor (benign or malignant): Tumors of the parotid gland, such as pleomorphic adenoma or adenocarcinoma, can present as a firm, fixed preauricular mass. The parotid gland is located in the preauricular area, making it a likely source of such masses.
First branchial cleft cyst: These congenital anomalies can present as a firm, fixed mass in the preauricular area, often becoming apparent during childhood but can also be diagnosed in adults.
Preauricular sinus or cyst: A congenital anomaly that can become infected and present as a firm, fixed, and possibly painful mass in the preauricular area.

Malignant lymphoma: Although less common, lymphoma involving the lymph nodes in the preauricular area can present as a firm, fixed mass. Given its potential for serious consequences, it is crucial not to miss this diagnosis.
Metastatic disease to the parotid gland or lymph nodes: Metastasis from other primary sites can present as a firm, fixed preauricular mass, emphasizing the importance of a thorough diagnostic workup.

Warthin's tumor: A rare, benign tumor of the salivary glands, which can present in the preauricular area, especially in older males.
Kimura disease: A rare, chronic inflammatory disorder that can cause lymphadenopathy and the formation of subcutaneous nodules, potentially in the preauricular area.
Sarcoidosis: Although rare, sarcoidosis can involve the lymph nodes and salivary glands, potentially presenting as a firm, fixed preauricular mass.