In this review, the value of imaging in the management of head and neck tumors is summarized. The many diverse tumors of the head and neck are grouped for purposes of staging and treatment. The groupings of malignancies consist of sinonasal, nasopharynx, salivary gland, oral cavity, oropharynx, hypopharynx, larynx, and thyroid tumors. The anatomy, rationale for choice of imaging modality, interpretation of acquired images, staging, treatment options, and posttherapy assessment are discussed.
Key points
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Imaging is an integral part of management of patients with head and neck cancers. Imaging provides information for accurate staging, therapy selection, therapy assessment, detection of recurrence, and predicting survival outcomes.
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Computed tomography (CT) or magnetic resonance imaging (MRI) is useful for primary tumor staging. Ultrasonography and positron emission tomography (PET)/CT are more useful for identifying neck nodal metastasis, and PET/CT is useful for detecting distant metastasis. MRI is useful for detecting perineural spread, marrow, skull base, and intracranial involvement.
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Posttherapy assessment is performed using CT/MRI or PET/CT. PET/CT is increasingly used for posttherapy assessment because of superior sensitivity and specificity, especially in patients treated with chemoradiation therapy. Fluorodeoxyglucose PET/CT is usually performed 12 weeks after completion of therapy.
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The best value of imaging in follow-up is when it is used with clinical assessment and suspicion for disease recurrence.
Introduction: nature of the problem
Head and neck cancers constitute approximately 3% of all cancers in the United States, with approximately 52,000 new cases diagnosed every year. Head and neck cancer include cancers that have developed in the nasal cavity, sinuses, lips, mouth, salivary glands, paranasal sinuses, pharynx, throat, or larynx. Most head and neck cancers (90%–95%) are squamous cell carcinomas arising from mucosal linings of the upper aerodigestive tract. Other rare cancers that may involve the head and neck include salivary tumors, thyroid cancers, lymphoma, and melanoma.
Tobacco and alcohol use are the most important risk factors for most head and neck cancers. Approximately 75% of head and neck cancers are caused by tobacco and alcohol use. Infection with certain types of human papillomavirus causes more than half of all cases of oropharyngeal cancer.
Early diagnosis and accurate staging are essential for treatment planning and can strongly influence prognosis. In addition, early identification of tumor recurrence can often be treated with additional surgery or reirradiation. A combination of history, physical examination, endoscopy, and tissue sampling has historically been the mainstay of diagnosis and staging. The use of advanced imaging with computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET)/CT has greatly improved staging, therapy assessment, and monitoring for disease recurrence.
Preimaging planning
Relevant Anatomy
The anatomy of the head and neck is a broad and complex subject, which is best appreciated when taken into context with the primary malignancy of interest. This review is by no means exhaustive but rather highlights the important structures from an imaging perspective as pertain to tumor spread and stage.
Sinonasal
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Malignant neoplasms include squamous cell carcinoma, adenoid cystic carcinoma, adenocarcinoma, olfactory neuroblastoma (esthesioneuroblastoma), melanoma, and lymphoma.
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The sinonasal cavity begins at the nostrils and ends at the posterior nasal septum, which separates it from the nasopharynx. The nasal cavity contains 3 medial bony projections, known as the turbinates, which originate in the lateral walls.
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The paranasal sinuses consist of the maxillary, ethmoid, frontal, and sphenoid sinuses. The maxillary sinuses form the inferior margin of the nasal cavity, whereas the superior maxillary sinus forms the orbital floor and contains the infraorbital groove, through which the infraorbital nerve runs. The frontal sinuses anteriorly contribute to the orbital roof. The sphenoid sinus posteriorly forms the nasopharynx roof. The ethmoid sinus forms the superior lateral and medial walls of the nasal cavity.
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The most common malignancy is squamous cell carcinoma. It may originate in the maxillary sinuses (60%–70%), followed by the nasal cavity (20%–30%), then the ethmoid sinuses (10%–15%), and rarely, in the frontal or sphenoid sinuses (1%).
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The second most common malignancy, adenocarcinoma, most commonly originates in the ethmoid sinus.
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Tumor can invade in several different directions :
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From the maxillary antrum posterolaterally to the pterygoid plates, pterygopalatine fossa, and infratemporal fossa
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From the pterygopalatine fossa to the orbit via the inferior orbital fissure or to the middle cranial fossa via the foramen rotundum
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From the maxillary antrum superiorly to the anterior cranial fossa and posterior wall of the frontal sinus via the orbital floor or the cribriform plate of the ethmoid
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Inferiorly to the maxillary ridge and hard palate
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Inferolaterally to the buccal space
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Medially to the nasal cavity
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Salivary gland
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The major salivary glands consist of the parotid, submandibular, and sublingual glands, and the minor salivary glands are distributed within the mucosa of the oral cavity, palate, paranasal sinuses, pharynx, larynx, trachea, and bronchi.
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Most parotid gland tumors are benign (80%), and only 20% to 25% are malignant. The probability for malignancy in the submandibular gland is about 40% to 50%. The risk of malignancy in sublingual and minor salivary glands is the highest, ranging from 50% to 81%. Unlike the major salivary glands, 80% or more of minor salivary gland tumors are malignant and tend to have a great variation in presentation and histology.
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The largest salivary gland, the parotid, is located in the parotid space; it is wedge shaped and is divided into superficial and deep lobes by the facial nerve and its branches for surgical planning. The facial nerve is best visualized radiographically by a line drawn from the lateral border of the posterior belly of the digastric muscle and the retromandibular vein to the lateral edge of the mandible.
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The auriculotemporal nerve connects the mandibular branch of the trigeminal nerve with the facial nerve and is embedded in the gland capsule as it curves around the mandibular neck and serves as a potential route of perineural tumor spread. Between 3 and 24 lymph nodes are found within the parotid gland within the superficial portion and drain into the level 2A and 2B cervical nodes.
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The submandibular gland is located in the submandibular triangle, which is formed by the inferior border of the mandibular body and anterior and posterior bellies of the digastric muscle. The stylohyoid muscle contributes to the posterior border as well. The submandibular gland does not contain any lymph nodes or large nerves, unlike the parotid. Lymphatic drainage of the submandibular gland is mainly through 1B or submandibular and deep cervical nodes, especially 2A nodes.
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The sublingual gland is the smallest major salivary gland; it is located above the mylohyoid muscle, is covered by mucosa of the floor of the mouth, and has no capsule. Primary lymphatic drainage is into level I cervical nodes.
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There are about 450 to 750 minor salivary glands in the head and neck region, which distribute into the sinonasal cavities, oropharynx, larynx, and trachea with most being found in the oral cavity. Heterotopic minor salivary glands can occur in the lymph nodes, the capsule of the thyroid gland, facial bones, and the hypophysis. Benign and malignant salivary tumors can occur at any of these sites, including heterotopic locations.
Nasopharynx
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The nasopharynx is located in the upper aerodigestive tract. It encompasses the superior aspect of the pharynx, which includes the lateral pharyngeal recess, the torus tubarius, and the pharyngeal tonsil
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Nasopharyngeal carcinomas are classified into (1) squamous cell carcinomas, which account for 70% to 98% of nasopharyngeal malignancy, (2) differentiated (subtype 2a) and undifferentiated (subtype 2b) nonkeratinized carcinomas, and (3) undifferentiated carcinomas.
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The nasopharynx is bordered by the posterior nasal cavity anteriorly, the clivus posteriorly, the carotid spaces laterally, the hard palate, and the palatopharyngeal muscle inferiorly.
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It is made up of 3 layers:
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Inner mucous lining made up of ciliated pseudostratified epithelium and chorium. There is abundant lymphoid tissue in the chorium; it is a frequent site of malignancy, such as non-Hodgkin lymphoma.
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Middle fibrous membrane or the pharyngobasilar fascia. This fascia is a tough aponeurosis, which connects the superior constrictor muscles to the skull base. The buccopharyngeal fascia is the middle layer of the deep cervical fascia, and it represents the fascial limit of the lateral and posterior portions of the nasopharynx.
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Outer muscular layer made up of upper, middle, and lower pharyngeal constrictor muscles, pharyngeal levator muscles (palatopharyngeal, stylopharyngeal, and salpingopharyngeal), palatoglossus, tensor palati and levator palati, and the palatopharyngeal muscle.
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The nasopharynx is 2 cm in anteroposterior diameter and 4 cm long.
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The sinus of Morgagni is a posterolateral defect in the pharyngobasilar fascia, which contains the paired eustachian tubes and the medial fibers of the levator veli palatini muscle.
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The lateral pharyngeal recess (fossa of Rosenmüller) is posterior and superior to the torus tubarius (the distal cartilaginous end of the eustachian tube, which can be seen projecting into the lumen of the nasopharynx).
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The parapharyngeal space separates the nasopharynx from the masticator space laterally and is a fibrofatty space; invasion of this space is used in staging.
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The lateral retropharyngeal nodes (nodes of Rouvière) and the cervical level II nodes are the most common sites of metastasis.
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Tumor invasion: 60% to 90% of the time, the tumor pushes through the pharyngobasilar fascia and invades the parapharyngeal space. The most common direction of invasion is superiorly (48%) into the skull base, with bone destruction seen on CT in or around the clivus, foramen lacerum, middle cranial fossa, sphenoid sinus, or foramen jugularis. The second most extension is posteriorly (40%) into the prevertebral muscles toward the retropharyngeal space. Invasion into the retropharyngeal space has a higher risk of distant metastasis because of the presence of a venous plexus and lymphatics. The remaining sites of direct invasion are in the anterolateral extensions toward the masticator space and infratemporal fossa (14%) or inferiorly through the lateral walls of the pharynx or posterior tonsillar pillars into the oropharynx.
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Perineural spread to the skull base can occur from the retropharyngeal space via multiple foramina, commonly with involvement of the fifth cranial nerves. Also commonly involved is the nerve of the pterygoid canal, which enters the pterygopalatine fossa and joins the pterygopalatine ganglion, from which postganglionic parasympathetic fibers distribute to various structures, including the nose and palate.
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The most common sites of metastasis include bone (20%), lung (13%), and liver (9%).
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The nasopharynx and oropharynx overlap and an acceptable line between the 2 is the C1/C2 junction.
Oral cavity and oropharynx
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The oral cavity is bordered by the maxilla and mandible and contains the lips, tongue (anterior two-thirds reside in the oral cavity), floor of the mouth, retromolar trigone, gingiva, alveolar ridges, and the hard palate.
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The nasopharynx is the most superior portion of the pharynx and extends from the skull base to the level of the hard/soft palate junction. The oropharynx consequently includes the posterior third of the tongue, the soft palate, palatine tonsils, and tonsillar pillars and extends to the level of the hyoid bone at the pharyngoepiglottic folds. The hypopharynx then extends inferiorly to the postcricoid segment, and the piriform sinuses.
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The most common sites of oral cavity cancer are the lips followed by the floor of the mouth. The common regions of involvement in the tongue include the lateral borders and the undersurface.
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Oral cavity cancers invade the pterygomandibular raphe (between the medial pterygoid plate and the mandible, separating the anterior tonsillar pillar and retromolar trigone) and extend to the temporalis muscle superiorly, the pterygopalatine fossa anteriorly, the pterygomandibular space medially, or the floor of the mouth inferiorly.
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The primary drainage site of the oral cavity is the level I submental and submandibular lymph nodes, and the level II jugular chain.
Larynx and hypopharynx
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The larynx can be divided anatomically into 3 parts: supraglottic, glottic, and subglottic.
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The hypopharynx can be divided into pyriform sinus, postcricoid area, and posterior pharyngeal wall.
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Important pathways of tumor spread in the larynx occur along the paraglottic and pre-epiglottic spaces.
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Invasion of the laryngeal cartilages is generally associated with poor prognosis. It affects staging as well as surgery planning.
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Pyriform sinus carcinomas invade the paraglottic space and the laryngeal cartilages and tend to spread superiorly and inferiorly. Tumors arising from the lateral wall of the pyriform sinus have a tendency to infiltrate the soft tissues of the neck early in the disease course.
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Postcricoid carcinomas spread submucosally, often toward the cervical esophagus.
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Posterior pharyngeal wall tumors commonly involve both the oropharynx and hypopharynx, and invasion of surrounding structures is unusual at initial presentation.
Thyroid
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The thyroid gland lies at the level of the C5-T1 vertebra. It has 2 lobes, joined by an isthmus. About 30% to 50% of normal individuals have a pyramidal lobe, which is a superior extension of the thyroid tissue.
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Extraglandular lymphatics generally follow the venous flow. The inferior portions of the lateral lobes drain along the tracheoesophageal groove into the central neck. The superior parts of the lobes drain toward the superior thyroid veins, and the isthmus may drain toward the prelaryngeal lymph nodes or central neck nodes.
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Even although it is uncommon, lymphatic drainage to the retropharyngeal region has been reported, accounting for metastasis to the skull base.
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The central lymphatics are considered the primary drainage pathway for thyroid cancer, and the lateral neck nodes are the secondary drainage pathway. Most thyroid cancers metastasize to the central compartment nodes (level VI).
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In large series, the lateral neck nodes are involved to varying degrees. Most commonly involved is level IV, followed by levels III, V, II, and I. Level I nodal metastases are rare from thyroid cancer.
The most commonly involved contralateral compartment is the paratracheal region. When this finding is positive, the risk for metastases to the lateral neck is higher.
Rationale/issues for modality selection
The choice of modality selection can depend on multiple factors. Factors such as insurance coverage, availability of imaging equipment, availability of experienced readers, and the stage of a patient’s malignancy can often dictate the choice of the primary modality used. CT is best suited to define the primary tumor and to identify bony invasion but can also be used for guiding tissue biopsy. MRI is best suited to delineate the extent of the primary tumor and involvement into adjacent structures. PET/CT is used to stage the locoregional lymph nodes and for systematic staging, and to assess posttherapy response or recurrence. In addition, patient contradictions such as contrast allergy (gadolinium or iodine), metallic implants (eg, pacemaker, cochlear implant), or pediatric population (concern for cumulative radiation dose) can affect choice of imaging modality. PET/MRI, although not widely available, holds promise in patients with head and neck malignancy, but research is limited compared with other imaging modalities. Tables 1–6 present the rationale for imaging modality selection and highlight the commonly recommended first choice.
| Ultrasonography | CT | MRI | PET/CT |
|---|---|---|---|
| Limited role | CT provides bony detail when looking at bone invasion as well as anatomic landmarks at the skull base The detailed anatomy of the ostiomeatal complex as shown by CT provides a road map for the surgeons before endoscopic sinus surgery | Used for mapping the extent of tumor, because of its multiplanar capability, superior soft tissue contrast Modality of choice for assessing primary tumor and for assessing orbital and intracranial involvement | Useful for neck nodal and systemic staging, especially in advanced tumors and to assess tumor response after radiation therapy Imaging is typically performed 3 mo after radiation therapy to decrease the false-positive results from inflammatory processes |
| Ultrasonography | CT | MRI | PET |
|---|---|---|---|
| Used for fine-needle aspiration for nodal staging Can assess tumor vascularity | Limited role; useful for bone invasion | Exact tumor localization and extent of tumor can be assessed (axial T1-weighted and T2-weighted images) Can detect perineural spread (T1-weighted axial and coronal images postgadolinium with fat suppression) | Useful for detecting locoregional and distant metastases in advanced stage |
| Ultrasonography | CT | MRI | PET |
|---|---|---|---|
| Limited role | Inferior to MRI for invasion into surrounding soft tissue | Can detect tumor invasion into surrounding soft tissue, pharyngobasilar fascia, sinus of Morgagni, as well as skull base and intracranial invasion Best to detect nerve involvement and perineural spread | Superior to MRI and CT for assessing lymph node metastasis, especially cervical nodal metastases, and distant metastases Modality of choice for therapy assessment and for follow-up with systemic staging Imaging for therapy assessment typically performed 3 mo after radiation therapy to decrease the false-positive results from inflammatory processes |
| Ultrasonography | CT | MRI | PET/CT |
|---|---|---|---|
| Limited to staging with fine-needle aspiration of neck nodes | Useful in detection of mandibular involvement Degraded to a greater extent than MRI in the presence of metal artifacts Modality of choice for primary tumor staging | Better than CT to evaluate primary tongue tumor thickness and for small tongue tumors Images degraded by patient motion artifacts of breathing and swallowing | Superior to MRI and CT for assessing cervical nodal metastases and distant metastases, especially with advanced stage Modality of choice for posttherapy assessment, especially after chemoradiation therapy and in follow-up for systemic staging Posttherapy assessment imaging is typically performed 3 mo after radiation therapy to decrease the false-positive results from inflammatory processes |
| Ultrasonography | CT | MRI | PET/CT |
|---|---|---|---|
| Limited role. Used with fine-needle aspiration for nodal staging | Modality of choice to assess primary tumor size, tumor infiltration of surrounding structures, and laryngeal skeleton destruction | Higher incidence of nondiagnostic results because of motion artifacts (caused by swallowing), compared with CT | Superior to MRI and CT for assessing cervical nodal metastases and distant metastases, especially with advanced stage Modality of choice for posttherapy assessment, especially after chemoradiation therapy and in follow-up for systemic staging. Posttherapy assessment imaging is typically performed 3 mo after radiation therapy to decrease the false-positive results from inflammatory processes |
| Ultrasonography | CT | MRI | PET/CT |
|---|---|---|---|
| Recommended modality of evaluation for contralateral lobe and cervical lymph node evaluation Used with fine-needle aspiration for staging | Useful in assessing the primary tumor extension into adjacent structures and for nodal staging | Useful in assessing the primary tumor extension into adjacent structures and for nodal staging | Incidental focal FDG thyroid uptake is associated with 24%–36% malignancy risk, with papillary thyroid carcinoma being the most common cancer Used in dedifferentiated papillary and follicular cancers in patients with increased thyroglobulin levels but negative radioiodine scintigraphy to detect recurrence and metastasis Shows high FDG uptake in Hurthle cell and anaplastic thyroid cancers not detected on conventional imaging. Useful for staging, therapy response assessment, and follow-up in these cancers |
Interpretation/assessment of clinical images
Table 7 shows the generally accepted features of benign and malignant tumors by choice of modality. Additional features of interpretation that are specific to the different types of head and neck malignancies are further discussed. A strong knowledge of anatomy and image interpretation is used for staging, according to the anatomic classification set forth by the American Joint Committee on Cancer.
| Imaging Features | Ultrasonography | CT | MRI | PET/CT |
|---|---|---|---|---|
| Benign | Hypoechoic or hyperechoic, well-defined, lobulated with posterior acoustic enhancement, homogeneous structure, peripheral eggshell calcifications | Hypodense, cystic soft tissue mass; preserved muscle border and bone cortex | Homogeneous signal intensity with low T1W and high T2W internal signals | Low FDG uptake compared with blood pool, generally |
| Malignant | Irregular shape, irregular borders, blurred margins, hypoechoic, and inhomogeneous structure; may have punctate calcifications and high vascularity | Soft tissue thickening, presence of a bulky mass and infiltration of adjacent tissue with or without bone destruction | Ill-defined, infiltrative border, heterogeneous internal signal with cystic change and necrosis; often with postcontrast heterogeneous enhancement | High FDG uptake compared with blood pool or liver uptake in FDG-avid tumors |
Sinonasal
CT is the modality of choice for inflammatory sinonasal disease, and malignancy is often found incidentally. When the diagnosis of malignancy is known, CT plays an important role because of its high sensitivity for erosion of the sinus walls not seen on MRI, and more importantly, it can establish involvement of the cribiform plate, which is used in staging of the tumor. Interpreting the coronal CT perpendicular to the bony palate is best suited for evaluation of the ostiomeatal complexes.
MRI is the modality of choice when it comes to staging primary sinonasal malignancy, because of its superior ability to differentiate tumor from surrounding tissue and fluid. Common landmarks for assessment of tumor involvement include the skull base, orbit, pterygopalatine fossa, and infratemporal fossa. The pterygopalatine fossa is an important landmark, because invasion of the fossa is a negative prognostic factor. It is by breaching the pterygopalatine fossa that intracranial extension can occur, and it is also the location where the trigeminal nerve branches pass through, making it possible for perineural spread of the primary tumor. When assessing orbital exenteration, bony erosion along with breach of the periosteum is a significant finding. When assessing orbital invasion, tumor adjacent to the periorbita (CT/MRI), extraocular muscle involvement (MRI), and orbital fat obliteration (CT or MRI) are sensitive predictors. On the other hand, extraocular muscle displacement and enhancement are less accurate ( Fig. 1 ).
