Head and Neck Imaging

Parotid gland

1. Anatomy

the largest salivary gland, situated below the external auditory canal and behind the ascending ramus of the mandible, reaching to the jaw angle. It is divided into a superficial and deep lobe by the branches of the facial nerve. The deep lobe reaches the prestyloid part of the parapharyngeal space. The parotid lobe drains through Stensens duct into the oral cavity. Also, see parotid gland.

Accessory parotid gland tissue is commonly seen along the course of Stensen's duct (anatomical variant).

2. Pathology

Congenital anomalies

  • agenesis of the parotid glands is very rare; it may be associated with other facial abnormalities.

  • a cyst arising from the first branchial cleft may be located within the parotid gland: see branchial apparatus.

    Inflammation

    Acute inflammation is commonly caused by sialolithiasis. Mumps is the most frequent acute infection of the parotid glands. Bacterial infection may lead to intraparotid abscess formation (Fig.1). Chronic inflammation may have an obstructive or nonobstructive aetiology. Also, see sialadenitis.

    Trauma

    Trauma to the parotid gland or duct may cause ductal stricture, leading to sialadenitis or formation of a sialocele. Ductal laceration may result in the development of a fistula, communicating with the skin or oral cavity.

    Tumour

  • The most common tumour is pleomorphic adenoma, usually appearing as a well circumscribed mass lesion in the superficial part of the parotid gland (Fig.2). Lesions arising from the deep lobe develop primarily within the parapharyngeal space and present late with symptoms related to pharyngeal compression (see parapharyngeal space (VI:2), Fig. 2). Also, see hemifacial spasm.

  • Warthins tumour is the second most common benign tumour of the parotid gland. Several other, but rare, benign tumours may be encountered in the parotid gland.

  • The most common malignant parotid tumour is mucoepidermoid carcinoma. Other malignant parotid tumours include adenoid cystic carcinoma, acinic cell carcinoma, adenocarcinoma head and neck and malignant pleomorphic adenoma. The parotid gland may be secondarily invaded by malignant tumours, for example arising from the external auditory canal, or by extranodal tumour spread from metastatic squamous cell carcinoma head and neck (Fig.3).

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    Fig.3

    Axial T2-weighted (a) and gadolinium-enhanced T1-weighted spin-echo images (b 1 cm caudal to c) of a patient with a history of left facial nerve paralysis for several months. Ill-defined soft tissue mass in the left parotid gland (asterisk); by perineural tumour spread along the auriculotemporal nerve (arrowhead, b-c), the neoplasm reaches the main stem of the mandibular nerve, causing denervation muscle atrophy of the masticator muscles (compare masseter muscles (arrows) and lateral pterygoid muscles (arrowheads, a).
    Parotid gland, Fig.1
    Parotid gland, Fig.2
    Parotid gland, Fig.3 (a)
    Parotid gland, Fig.3 (b)
    Parotid gland, Fig.3 (c)