The subzygomatic approach is ideally suited for the biopsy of lesions in different parts of the masticator space. This approach can also be used for sampling lesions in the parapharyngeal, pharyngeal mucosal, and retropharyngeal spaces and for the prevertebral portion of the perivertebral space. Lesions in the suprazygomatic portion (temporal fossa) of the masticator space and skull base, including the pterygopalatine fossa region, can also be accessed using this approach.

In the subzygomatic approach, the needle is inserted below the zygomatic arch and advanced through the intercondylar (mandibular) notch between the coronoid process anteriorly, the mandibular condyle posteriorly, and the superior border of the mandibular ramus inferiorly (Fig. 9.2). The needle can be angulated in various (anterior, posterior, cranial, or caudal) directions, allowing access to multiple target sites (Figs. 9.3 and 9.4). The needle traverses the masticator and the parapharyngeal spaces during biopsies of lesions located in the pharyngeal mucosal, retropharyngeal, and prevertebral spaces and skull base.

Cranial needle angulation allows the subzygomatic approach to be used for accessing lesions in the skull base and the suprazygomatic portion of the masticator space. Using a triangulation method, the physician estimates the needle angle from contiguous axial CT scans obtained from the level of the planned skin entry site to the level of the target lesion. The needle is inserted below the level of the zygomatic arch and advanced cranially and medially in small increments; axial CT scans are obtained to check the needle tip position and angulation (Fig. 9.5). Alternatively, a change in the degree of neck flexion can bring the target lesion and the skin entry site into the same axial plane, allowing visualization of the entire needle length in a single axial CT image.

It has been suggested that having the patient keep his or her mouth open, preferably with a bite block, can help open up the space between the mandible and the zygomatic arch, thus facilitating needle insertion; however, in our experience, as in that of others [2], this is rarely necessary.

With the sybzygomatic approach, there is a theoretical risk of injury to the mandibular branch of the trigeminal nerve, the internal maxillary artery and its branches (including the middle meningeal artery), and the pterygoid venous plexus. The maxillary artery arises posterior to the neck of the mandible and is embedded in the parotid gland. The mandibular part runs horizontally forward along the medial surface of the ramus and passes between the neck of the mandible and the sphenomandibular ligament. The pterygoid part ascends obliquely forward and medially, either superficially or deep to the lateral pterygoid muscle, to enter the pterygopalatine fossa through the pterygomaxillary fissure. The middle meningeal artery arises from the mandibular part of the internal maxillary artery and ascends in the posterior part of the sigmoid notch deep to the lateral pterygoid muscle to enter the foramen spinosum. The mandibular nerve exits the cranial cavity through the foramen ovale and descends in the posterior part of the intercondylar notch; the mandibular nerve runs downward medially to the lateral pterygoid muscle and a little anteriorly to the neck of the mandible to enter the inner surface of the mandibular ramus. The pterygoid venous plexus of veins is located partly between the temporalis and lateral pterygoid and partly between the two pterygoid muscles. However, as mentioned earlier, the risk of major injury to the vessels or the nerves is extremely low. A needle inserted posteriorly close to the mandibular condyle and directed anteriorly may occasionally pass through a small anterior portion of the parotid gland, but this usually does not cause problems (Fig. 9.2b).

Lesions in the deep parotid space, parapharyngeal space, pharyngeal mucosal space, and lower part of the retropharyngeal space are amenable to biopsy with a retromandibular approach. This approach can also be used for sampling lesions in the carotid sheath if the vessels are displaced medially by the mass.

With the patient in the supine position and his or her head turned to the contralateral side, the needle is inserted posterior to the mandible and anterior to the mastoid process and advanced through the parotid gland (which is located behind the mandible, extending from the external auditory canal to the level of the mandibular angle) toward the target lesion (Fig. 9.6). Care should be taken to identify and avoid the external carotid artery and the retromandibular vein, which are both located within the parotid gland immediately posterior to the mandibular ramus (Fig. 9.6). The external carotid artery is medial of the two vessels. Approximately midway between the tip of the mastoid process and the angle of the mandible, the external carotid artery turns laterally from the carotid sheath and passes anterior to the posterior belly of the digastric muscle to reach the posteromedial surface of the parotid gland. Within the substance of the parotid gland, the external carotid artery ascends behind the condyle and divides into its terminal branches, the superficial temporal and maxillary arteries. The seventh cranial nerve passes just lateral to the retromandibular vein (Fig. 9.1d). The styloid process serves as a useful bony landmark; keeping the needle anterior to the styloid process avoids injury to the internal carotid artery, which is located in a plane posterior to the styloid process (Fig. 9.7). Occasionally, however, medial displacement of the carotid vessels by mass lesions may allow the needle to be advanced posterior to the styloid process.

The presence of surrounding structures, such as the styloid process, internal carotid artery, mastoid process, and mandible, does not allow much room for needle angulation. Thus, it is difficult to access the skull base, the prevertebral space, the cervical spine, and portions of the retropharyngeal space with this approach (Fig. 9.8). The potential risk of injury to the facial nerve, which courses through the parotid gland, limits the size of the biopsy needle that can be used with this approach. The use of thin needles precludes the option of obtaining a core specimen. For a biopsy of deeper lesions, the needle passes through the parapharyngeal space, and there is a potential risk of injury to the mandibular nerve branches and branches of the internal maxillary artery, such as the middle meningeal and ascending pharyngeal arteries. Yousem et al. [20] pointed out that a transparotid biopsy may occasionally yield salivary gland tissue, which may be confused with a salivary gland neoplasm of the parapharyngeal space. However, we have not encountered this problem in any of our patients.

The paramaxillary approach offers safe access to lesions in the infrazygomatic portion of the masticator space, the posterior portions of the parapharyngeal and pharyngeal mucosal spaces, the carotid sheath space, and the deep portion of the parotid space [21, 22]. This approach is particularly useful for lesions in the lateral part of the retropharyngeal (e.g., lateral retropharyngeal node of Rouviere) space and prevertebral portion of the perivertebral space because these lesions are difficult to access by other approaches. The paramaxillary approach can also be used for sampling lesions involving the anterior arch of the first cervical vertebra (C1) and the odontoid and body of the second (C2). In addition, this approach can be used to access the foramen ovale and other skull base lesions by using a cranial needle angulation [23].

For the transfacial paramaxillary approach, the patient is placed in the supine position with his or her head turned to the contralateral side, and the needle is inserted through the buccal space inferior to the zygomatic process of the maxilla and advanced posteriorly between the maxilla (alveolar ridge or sinus) and mandible (Fig. 9.9). It is important to avoid the facial artery, which is easy to identify as it courses in the buccal space (Fig. 9.9). For biopsy of lesions in the masticator and parapharyngeal spaces, the needle passes through the buccinator muscle or anterior portion of the masseter muscle or between them (Fig. 9.10). The needle is advanced through the lateral and medial pterygoid muscles and the parapharyngeal space to biopsy lesions in the retropharyngeal (Fig. 9.11) and carotid space (Fig. 9.12) and C1 and C2 lesions (Fig. 9.13). This approach can also be used to access foramen ovale and other skull base lesions by using cranial needle angulation (Fig. 9.14). Effecting mild hyperextension of the neck by placing padding under the patient’s shoulders brings the skull base lesions and the skin entry site into the same axial plane and makes needle placement and visualization simple.