Evaluation of the head and neck has developed significantly with the advent of CT and MRI. These modalities have greatly complimented the physical and endoscopic examinations by revealing possible blind areas such as nonpalpable adenopathy, cartilage invasion, bone marrow invasion, contralateral involvement, and distant metastases. MRI has some major advantages over CT. Superior soft tissue contrast is possible with MRI leading to better definition between tumor and adjacent structures. Multiplanar imaging can be extremely helpful in appreciating and confirming the extent of disease. There is a lack of beam hardening artifacts which are encountered with CT when dental fillings are present. In patients who can not tolerate intravenous iodine contrast, MRI with gadolinium can still be performed. In order to optimally evaluate the head and neck for pathological processes, one must first have a clear understanding of the anatomy of the head and neck.

Anatomical Considerations:

In addition to understanding basic anatomical structures such as the tongue, the tonsilar fossa, the epiglottis, the paranasal sinuses, the nasal cavity, and the larynx, one must also be aware of certain anatomical spaces which are delineated by fascial planes. These anatomical spaces throughout the head and neck represent potential vertical highways for tumor spread of pathological processes.

Pharyngeal Mucosal Space:

This space is located very superficially along the pharyngeal mucosal walls. It includes the mucosa of the pharynx, Waldeyer's ring, the cartilaginous eustachian tube, the pharyngobasilar fascia, the levator and constrictor muscles. Common tumors seen in this space would include squamous cell cancer, lymphoma, and sometimes adenocarcinoma, adenoid cystic carcinoma, and juvenile angiofibromas. Thornwaldt cysts and mucous retention cysts can also be found along this space. It represents a very superficial layer for which tumors often will develop before they spread to deeper layers. This space is probably less important from an imaging standpoint than the deeper spaces as an endoscopist can usually detect tumor spread along this space without difficulty.

Parapharyngeal Space:

This is an important vertical highway which extends from the skull base to the hyoid bone. Tumors that may arise along the pharyngeal mucosal space such as squamous cell cancer of the tonsilar fossa, can spread to the next deeper layer which is often the parapharyngeal space. Once in the parapharyngeal space, it can spread in a vertical manner very quickly. The parapharyngeal space contains primarily fat, branches of the trigeminal nerves, and the pterygoid veins. Lesions that are frequently encountered in this space include metastatic lesions from squamous cell cancer, particularly from the base of the tongue, tonsilar fossa, and larynx. Salivary gland tumors may also be encountered in this space as a result of direct extension. Branchial cleft cysts can develop or cross through this space. Lipomas may arise denovo from the fat within this space. Infections can also run rampant in this space in a very rapid manner.

 

Carotid Space:

This is another major highway through which tumors can race vertically up and down from the skull base down to the aortic arch., This space includes the extracranial carotid artery, the jugular vein, portions of cranial nerves 9 through 11, the internal jugular chain of nodes. Metastatic lesions from squamous cell cancer can frequently be found in this space. Popular sites of origin for squamous cell cancer to invade the carotid space include the larynx, the tongue base, the tonsilar fossa, and the nasal pharynx. Other lesions that can be found in the carotid space would include neurofibromas, Schwannomas, paragangliomas, and lymphomas. Infections which may be harbored, particularly in the internal jugular nodes, can also be detected in the carotid space. Involvement of the carotid space may be an indicator for nonresectability, particularly if the carotid artery is encased.

Prevertebral Space:

This is a complex space which is enveloped by a deep layer of cervical fascia. It includes not only the longus coli muscles, but also the paraspinous muscles, the vertebra, the vertebral artery, and the spinal cord. Metastatic lesions to the prevertebral space as well as to the carotid space can potentially determine inoperability. For that reason, close scrutiny of tumor extension to the prevertebral space is very important. Common neoplasms that are found in the prevertebral space include metastatic lesions particularly from squamous cell carcinoma of the tonsilar fossa, the nasopharynx, the larynx, and the base of the tongue. Chordomas can also be found in this space. Infections from vertebral osteomyelitis and/or prevertebral abscesses may also be encountered in this area.

Submandibular Space:

This space contains the submandibular gland, submandibular nodes, and portions of the facial vein and artery as well as the inferior loop of cranial nerve 7. Squamous cell cancer from the base of the tongue and floor of the mouth can extend into this space. Other types of tumors involving this space may include the variety of salivary gland tumors ranging from mucoepidermoid to adenoid cystic to pleomorphic adenomas.

 

This space contains the parotid gland and the parotid segment of cranial nerve 7. The retromandibular vein in external carotid arteries also pass through this space. Common tumors in this location would include pleomorphic adenomas, Warthin's tumors, mucoepidermoid carcinomas, adenoid cystic carcinomas, hemangiomas, and squamous cell carcinomas.

Masticator Space:

This space contains the muscles of mastication. These include the masticator, temporalis, the medial and lateral pterygoids. Metastatic extensions of squamous cell carcinoma, particularly from the floor of the mouth, tonsilar fossa, and nasopharynx can be found extending into this space. Salivary gland tumors can also extend into this space. If neoplasm is discovered in this space, one should check for extension to the side of the skull as the masticator space extends very high into the suprazygomatic region along the temporalis muscle. One should also check for possible perineural spread, particularly along the course of the mandibular division of cranial nerve 5. Lymphomas and hemangiomas as well as cellulitis or abscesses can also be found in this compartment.

Retropharyngeal Space:

This is a posterior potential midline space which can also present a major highway extending cephalad to the skull base or caudad down to approximately the T3 level. Common lesions which can involve this space would include lymphomas, metastatic tumors, particularly from squamous cell cancer, and infections.

Lymph Node Evaluation:

We consider nodes to be suspicious for metastatic disease by size. In the jugular digastric region (levels 1, 2, and 3 or submandibular and upper internal jugular chain) nodes that are larger than 1.5 centimeters in diameter should be considered very suspicious for metastasis. Nodes in all other levels of the neck exceeding 1 centimeter in size, should be considered abnormal. Nodes with necrosis should also be considered abnormal regardless of size. One should also pay attention to nodes that have ill defined borders as there may be extracapsular extension with infiltration of the surrounding fat planes or encasement of vessels such as the carotid.

Abnormal supraclavicular nodes may represent metastasis from any source, but lung, breast, and esophagus are particularly common sources. Abnormal adenopathy along the inferior jugular chain may be due to metastatic disease from the supraglottic larynx, esophagus, or thyroid. Abnormal adenopathy in the midjugular chain may be related to

metastasis from tongue, pharynx, or supraglottic larynx cancers. Those along the jugular digastric region are often related to metastasis from the pharynx, tonsil, tonsilar fossa, tongue, parotid gland, or supraglottic larynx. Submandibular adenopathy may be related to metastasis from adjacent skin, submaxillary gland, or base of the tongue. Posterior triangle nodes may be seen with metastasis from the pharynx, the nasopharynx, tongue base, tonsilar fossa, or thyroid.

Coronal CT is usually the most functional projection for evaluating the paranasal sinuses. The osteomeatal complex represents a common drainage point for the anterior sinuses (frontal, ethnoid, and maxillary). A lesion placed at the osteomeatal complex can strategically obstruct the anterior sinuses.

Osteomeatal Complex: (Strategic point which a lesion can obstruct the anterior sinuses.) * Components: Infundibulum, uncinate process, ethmoid bulla, hiatus semilunaris, middle meatus, middle turbinate. * Concha Bullosum may act as an ethmoid air cell and should be reported. * Haller cell: laterally situated ethmoid cell which can potentially cause structural obstruction of outflow to maxillary sinus. * Olfactory cleft: obstruction may be a cause of anosmia. * Mucus retention cysts: obstructed mucus gland. Usually well-rounded and arises from side wall of sinus. * Mucocele: an obstructed sinus.

Inflammatory and/or allergic processes are usually seen as areas of mucoperiosteal thickening, fluid or airfluid levels filling the paranasal sinuses. In severe or complicated cases, bone changes (erosion or thickening) may be present.

A mucus retention cyst represents an obstructed gland. It is usually seen as a rounded soft tissue mass attached to the wall of a sinus.

A mucocele is an obstructed sinus. Bone expansion can be present with mucoceles.

Malignancies that affect the paranasal sinuses include squamous cell carcinoma, non-hodgkins lymphoma, and salivary malignancies.

Nasopharyngeal carcinoma tends to have a predilection for the fossa of Rosenmueller and therefore often presents with unilateral otitismedia or unilateral mastoiditis in adults. This tumor likes to spread along the spinal accessory chain of nodes and the suspicious node in the posterior triangle may therefore alert one to the presence of nasopharyngeal carcinoma. Likewise, the finding of unilateral otitismedia and/or mastoiditis in an adult, should direct one to the nasopharynx to be sure that there is not an early nasopharyngeal cancer lurking.

Non-Hodgkin's lymphoma is the second most common nasopharyngeal malignancy. Most are histiocytic or lymphocytic types of lymphomas. Hodgkin's lymphoma is very uncommon in the head and neck. Cervical lymph node involvement is common in non-Hodgkin's lymphomas of the head and neck and involvement of Waldeyer's ring is often seen. These tumors tend to be very bulky and can easily cross fascial planes.

Other malignancies that occur in the nasopharynx and paranasal sinuses can include tumors of the minor salivary glands which line the mucosal surfaces of the nasopharynx and paranasal sinuses.

These would include adenoid cystic carcinomas and mucoepidermoid carcinomas. Adenocarcinomas and rhabdomyosarcomas are also a possibility. Benign tumors would include inverted papilloma which arises from the mucous membranes, but invaginates inwardly into the underlying stroma. The common place for an inverted papilloma to arise would be the lateral nasal wall at the middle meatus. The inverted papilloma is a benign, slow growing lesion, which tends to remottle and enlarge the nasal fossa. It tends to grow inwardly, particularly into the maxillary sinuses, causing obstruction and possibly bone destruction. Epistasis can also be associated with this tumor.

Juvenile nasal angiofibroma

s tend to be seen in teenage males and usually originate along the pterygopalatine fossa. They are extremely vascular and can follow blood vessels commonly out to the infratemporal fossa, orbit, and possibly also into the middle cranial fossa. They can represent with nasal obstruction and epistasis. One should check for numerous flow voids and widening of the pterytopalatine foramen.

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9. Drawings adapted from: Harnsberger H, Osborn A. Differential diagnosis of head and neck lesions based on their space of origin. I. The suprahyoid part of the neck. AJR 157:147-154, July 1991.