Head and Neck Imaging

Parapharyngeal space

1. Anatomy

The parapharyngeal space is a deep space in the neck in the shape of an inverted pyramid with its base attaching to the skull base and the apex reaching the level of the hyoid bone. It is bordered on its medial side by the naso- and oropharynx, on its anterolateral side by the masticator space, on its posterolateral side by the deep lobe of the parotid gland, and on its posteromedial side by the retropharyngeal space. Some authors limit the parapharyngeal space to the fatty space anterior to the carotid space, while others consider the suprahyoid part of the carotid space to be part of the parapharyngeal space. Another approach is to divide the parapharyngeal space into two compartments, using the tensor veli-styloid fascia as separating layer. This fascial layer runs between the tensor veli palatini muscle, styloid process and styloid musculature; the prestyloid compartment is anterolateral, and the retrostyloid compartment is posteromedial to this fascial layer and includes the carotid space.

2. Pathology

Intrinsic parapharyngeal space pathology

  • Retrostyloid compartment

    Apart from vascular pathology, such as internal carotid aneurysm, dissection or thrombosis and internal jugular vein thrombosis, tumoral pathology arising either from the lower cranial nerves (see neurogenic tumour head and neck) or from the glomus bodies (glomus tumour) may be seen in the retrostyloid compartment. Mass lesions in this location typically displace the internal carotid artery anteromedially and the internal jugular vein posterolaterally (Fig.1); carotid space (VI:2), Fig. 1.

  • Prestyloid compartment

    Lesions in the prestyloid compartment lie anterior to the internal carotid artery and internal jugular vein. Solid mass lesions are usually of accessory salivary gland origin. Anomalies from the branchial apparatus may be encountered.

    Extrinsic parapharyngeal space pathology

    The parapharyngeal space can be displaced or invaded by pathology arising from the surrounding spaces. The loose fatty parapharyngeal tissue may be used as a 'lift shaft' by pathological conditions originating from neighbouring structures.

  • parotid space: tumours arising from the deep lobe of the parotid gland commonly extend into the prestyloid compartment. Differentiation from a primary prestyloid lesion may be difficult. The most reliable sign of a primary parapharyngeal tumour is the presence of a fat layer separating the tumour from the deep lobe of the gland; a more or less dumbbell-shaped mass widening of the stylomandibular tunnel, combined with anteromedial displacement of the parapharyngeal fat, suggests a primary parotid lesion (Fig.2).

    Parapharyngeal cellulitis may be seen secondary to parotitis (parotid gland (VI:2), Fig. 1).

  • pharynx: pharyngitis may cause parapharyngeal cellulitis; malignant tumours from the oro- or nasopharynx may extend into the pre- and/or retrostyloid compartment (see oropharynx cancer (VI:2), Fig. 3). Such an extension pattern is particularly common in nasopharyngeal cancer (see nasopharynx cancer).

  • masticator space: mass lesions from the masticator space may displace the parapharyngeal fat posteromedially.

  • retropharyngeal space: large retropharyngeal adenopathies displace the parapharyngeal fat anterolaterally.

  • mass lesions arising from the submandibular space [HN]  or skull base may extend into the parapharyngeal space.

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    Fig.1

    Axial T1-weighted spin-echo image in a patient with known neurofibromatosis. A large enhancing soft tissue mass is seen in the retrostyloid compartment of the parapharyngeal space, displacing the internal carotid artery (arrow) anteromedially (the internal jugular vein cannot be identified on this image). The fat of the prestyloid compartment is displaced anteriorly (arrowhead).
    Parapharyngeal space, Fig.1
    Parapharyngeal space, Fig.2 (a)
    Parapharyngeal space, Fig.2 (b)
    Parapharyngeal space, Fig.2 (c)