A wide variety of tumors present in the sinonasal and ventral skull base. Patients often have nonspecific symptoms initially and present with advanced tumors, affecting the orbit and other adjacent structures. Evaluation of these malignancies with modern imaging techniques can define tumor invasion, but biopsy is often required to establish a diagnosis because most have a nonspecific appearance. A thorough understanding of the anatomy is the key to treatment planning, and a multidisciplinary approach determines the optimal strategy.
Key points
- •
Work-up of sinonasal and ventral skull base malignancies requires thorough history and physical examination, augmented by modern imaging techniques and histological evaluation.
- •
Lesions of the paranasal sinuses and ventral skull base often present in advanced stages, involving adjacent structures. Optimal treatment planning requires a multidisciplinary approach involving otolaryngology, ophthalmology, neurosurgery, plastic and reconstructive surgery, and oncology teams.
- •
The wide variety of cell types gives rise to an uncommon group of pathology. Definitive treatment requires an understanding of their etiologies and pattern of spread.
Introduction
The paranasal sinuses are a complex framework of air cavities with a wide range of tissue types. They give rise to both benign and malignant tumors that present with variable signs and symptoms, depending on their origin and spread. This article provides a summary of the clinical presentation of sinonasal and ventral skull base lesions, establishment of diagnosis, modern imaging technology, and histopathology of the most common tumors.
Introduction
The paranasal sinuses are a complex framework of air cavities with a wide range of tissue types. They give rise to both benign and malignant tumors that present with variable signs and symptoms, depending on their origin and spread. This article provides a summary of the clinical presentation of sinonasal and ventral skull base lesions, establishment of diagnosis, modern imaging technology, and histopathology of the most common tumors.
Epidemiology
Although the incidence of overall sinonasal lesions is low, approximately 3% of computed tomography (CT) scans of the paranasal sinuses obtained reveal an osteoma. Malignancies also account for only 3% to 6% of total head and neck neoplasms. There are known variations, however, across gender (2:1 male-to-female predilection), occupational exposure (woodwork dust, chrome, and nickel), and geography (higher incidence in Japan and Africa). As for site of origin, the maxillary sinus is the most commonly involved followed by the ethmoids. Tumors arising in the paranasal sinuses have space to grow, and signs and symptoms are nonspecific, resulting in advanced staging at presentation. Unilateral nasal obstruction is the most common complaint.
Clinical presentation
Thorough history and physical examination, aided by high-definition endoscopic procedures, are the cornerstones of head and neck tumor diagnosis. For the general practitioner, early sinonasal tumors may only present with nasal obstruction, epistaxis, or obstructive pansinusitis. Unilateral complaints should raise the index of suspicion, as with signs and symptoms of adjacent structures ( Table 1 ). A comprehensive list of common presenting symptoms and history is in Box 1 .
| Early | Advanced |
|---|---|
| Unilateral epistaxis, sinusitis, obstruction Swelling of the upper gingiva or loose dentition Headache Hyposmia | Anesthesia of the skin of the cheek and upper lip (V2 distribution) Diplopia Proptosis Recurrent epistaxis Nasal obstruction refractory to medical therapy Palatal mass Trismus (invasion into the pteryoids) Cranial palsy (III, IV, and VI) Anosmia |
Facial pain or pressure
Nasal obstruction
Anterior or posterior purulent drainage
Hyposmia or anosmia
Fever
Headache
Halitosis
Dental pain
Fatigue
Cough
Ear pain
Vision changes
Epistaxis
Current sinonasal medications
Number of sinus infections per year requiring antibiotics
Prior sinonasal surgery
Known history of polyps
History of allergy testing and immunotherapy
Environmental allergies
Aspirin sensitivity
Occupation
Asthma
Smoking history
History of autoimmune disease
History of immune deficiency
Physical examination
Tumors of the nasal cavity and paranasal sinuses are often the most challenging to examine. Both flexible and rigid endoscopy require adequate topical anesthesia and patient reassurance. Patients are prepped with application of atomized 4% lidocaine and oxymetazoline (or equivalent decongestant). Flexible nasolaryngoscopy provides adequate visualization of most intranasal lesions, with the extended capability of evaluating for nasopharyngeal and oropharyngeal extension. Rigid telescopes are generally preferred for high-definition characterization of lesions, office procedures, and video recording for pretreatment and post-treatment evaluation. A well-equipped examination room should be fitted with 2 monitors, with 1 facing the patient to provide reassurance, video recording, and storage console; a set of 0°, 30°, and 70° Hopkins rod telescopes (Karl Storz, Germany); and instruments for suctioning and débridement ( Fig. 1 ). Adult rigid endoscopes are typically 4 mm in diameter and can be substituted with pediatric 2.7-mm endoscopes for patient comfort.
Due to ventral skull base lesions’ proximity to cranial nerves, orbits, and important vasculature, a complete head and neck examination is advocated. An overall survey should note gross facial deformity, and, if present, in-office photography is performed with base view, profile view, three-quarter view, and frontal view. Any facial incisions, external resection, flaps and grafts, and possible orbital exenteration should be discussed in conjunction with the neurosurgical and facial plastics team. As the number of tumors amenable to endoscopic resection grows, a patient-oriented approach and setting-appropriate expectations are the hallmarks of a rhinology practice.
In addition to the directed endoscopic view of the lesion, a systematic neurological examination of the cranial nerves is often warranted. Proptosis from mass effect and cranial nerves III, IV and VI palsies are frequent orbital complications of sinonasal tumors. Intraocular pressures, visual field testing, visual acuity, and afferent visual defect should be performed with a consultation with an ophthalmologist prior to treatment. Assessment of cranial nerve V should include light and sharp discrimination in all 3 divisions.
A detailed review of system may also direct physical findings that warrant consultations. It is not uncommon for patients to complain of unilateral hearing loss, possibly from the obstruction of the eustachian tube orifice leading to middle ear effusion and conductive hearing loss. For advanced tumors involving the maxillary sinus floor, loose teeth and palatal swelling can lead to malfitting dentures. Symptoms from metastasis may also precede any from the primary tumor. Sinonasal tumor spread is seen with high cervical lymph nodes and occasionally to the node of Rouvière, the highest retropharyngeal lymph node in the neck.
Diagnostic procedures
The skull base represents a bony partition between intracranial contents and the nasal cavity, paranasal sinuses, and the orbit. It also contains foramina and fissures that transmit vessels and nerves that serve as pathways for tumor extension. Tumor involvement of such structures can only be assessed indirectly prior to surgery, and modern imaging techniques allow accurate assessment of tumor location, origin, extent of involvement, relationship to vessels and nerves, and adjacent organs.
Imaging Techniques: Computed Tomography
CT is the method of choice for assessment of osseous structures. CT is a widely available technique and is carried out using 5-mm sections during a single acquisition. Thinner sections are often required to provide the high anatomic detail of the skull base, and typically 1-mm sections are used to provide reconstructions into axial, sagittal, and coronal planes. The advantages and disadvantages of the technique are summarized in Table 2 .
| Advantages | Disadvantages |
|---|---|
| Excellent for bony structures, foramina, fissures, carotid canal, and calcification within the tumor Widely available Fast | Inadequate for dura, meninges, and brain Ionizing radiation (especially for children) Allergy (iodinated contrast) Artifacts from dental restorations Difficult to differentiate obstructed secretions from tumor without contrast |
Imaging Techniques: MRI
MRI is the method of choice for assessment of soft tissues (dura, meninges, and brain) and tumor, after introduction of gadolinium contrast agent. MRI is often performed using 3-mm sections, and T1-weighted and T2-weighted sequences are used for evaluation of the anatomy (T1-weighted images) and lesion characterization (T2-weighted images). Magnetic resonance angiography is also used to define vascular anatomy and vascularity of lesions.
Cortical bone of the skull base is typically indicated by a signal void, with fatty marrow demonstrating signal intensity in T1-weighted images. Irregular signal void of the bony cortex often suggests invasion by the tumor ( Fig. 2 ). Although the tumor is hyperintense in postcontrast T1-weighted sequences, comparison to precontrast images is important to differentiate fat from lesion. For this reason, fat-suppression technique has been developed to define intracranial extension and differentiation between cystic and solid lesions. It has also helped define perineural spread into the foramina because perineural invasion obliterates the fat at the extracranial openings. On T2-weighted images, MRI is used to evaluate the cavernous sinus, with loss of hyperintensity of the cerebrospinal fluid–containing Meckel cave. The carotid artery is well seen as a signal void passing through the skull base, with narrowing of the lumen suggesting invasion. Comparison with CT images for bony dehiscence is mandatory for preoperative planning.
Paranasal and ventral skull base lesions
The skull base is composed of 5 bones: ethmoid, sphenoid, occipital, paired temporal, and paired frontal bones. The anterior part of the ventral skull base separates the anterior cranial fossa from the paranasal sinuses and orbits ( Fig. 3 ). The anterior border is formed by the posterior wall of the frontal sinus and the posterior border is formed by the planum sphenoidale and anterior clinoid processes. The frontal bone forms the lateral limit, with the ethmoid bone forming the central part of the floor. The center is the cribriform plate, which has small perforations for the olfactory nerves to pass. The lateral wall is formed by the fovea ethmoidalis, or the roof of the ethmoid cavity.
A variety of lesions are encountered in the ventral skull base, and the pterygopalatine fossa serves as a portal for perineural spread and intracranial involvement. Posteriorly it contains foramen rotundum and the vidian canal; anteriorly it contains the inferior orbital fissure; medially it contains the sphenopalatine foramen, laterally it contains the pterygomaxillary fissure to communicate with the masticator space; and inferiorly it contains the greater and lesser palatine foramina.
Tumor types: epithelial tumors
Inverted Papilloma
All sinonasal papillomas derived from the surface mucosa of the sinonasal tract (also known as schneiderian membrane) and there are 3 different histological subtypes. Exophytic or septal-type papillomas consist of broad-based papillary projections with well-developed fibrovascular cores. The papillae are lined by stratified squamoid to transitional epithelium with scattered mucocytes as well as rare ciliated columnar cells. On the other hand, inverted papillomas arise on the lateral nasal wall and are characterized by variably thickened stratified squamoid to transitional epithelium growing downward into the underlying stroma ( Fig. 4 ). The identification of mucocytes, intraepithelial mucous cysts, and mixed acute and chronic inflammation is characteristic. Oncocytic or cylindrical papillomas also arise on the lateral nasal wall but are composed of stratified columnar cells with abundant eosinophilic to granular cytoplasm. These lesions can show endophytic and/or exophytic growth, and cysts limited to the epithelium containing neutrophils are typically seen. Transformation to carcinoma has been reported in inverted (approximately 10%) and oncocytic (4%–17%) types and rarely in exophytic papillomas. Conventional keratinizing squamous cell carcinoma (SCC) is the most common carcinoma arising in sinonasal papillomas and most commonly it occurs synchronically; consequently, the presence of extensive keratinization in a sinonasal papilloma should prompt thorough histological examination.
An etiological association between human papillomavirus (HPV) and sinonasal papillomas has been proposed. According to different series, HPV DNA, most commonly types 6 and 11, has been detected in approximately half and one-third of exophytic and inverted papillomas, respectively. No link between HPV and oncocytic papillomas, however, has been established. Recently, the role of HPV in sinonasal papillomas has been challenged by a study that identified recurrent activating EGFR mutations in approximately 90% of inverted papillomas. A majority of these mutations are exon 20 insertions and the mutational status showed strong negative correlation with HPV DNA detection. In addition, KRAS exon 2 mutations have been reported in a majority of oncocytic papillomas. The same EGFR and KRAS mutations are identified in the SCC associated with inverted and oncocytic papillomas, respectively.
CT appearance of inverted papillomas is nonspecific, with polypoid lesion originating from the lateral nasal wall. Occasionally it may originate from the nasal septum showing a lobulated mass. Focal bone remodeling and sclerosis can also be seen. Multiplanar CT is essential in assessing the extent of disease. MRI is rarely obtained for unsuspecting disease, but a characteristic columnar pattern may be seen reflecting layers of proliferating epithelium invaginating in the underlying stroma (see Fig. 4 ). The hyperplastic epithelium appears hypointense on T2-weighted images due to hypercellularity, and the underlying stroma shows hyperintensity on T1 postcontrast images due to hypervascularity ( Fig. 5 ). The Krouse staging system for inverted papilloma is included in Table 3 .
| T1 | Tumor totally confined to the nasal cavity, without extension into the sinuses. The tumor can be localized to 1 wall or region of the nasal cavity or can be bulky and extensive within the nasal cavity but must not extend into the sinuses or into any extranasal compartment. There must be no concurrent malignancy. |
| T2 | Tumor involving the ostiomeatal complex, and ethmoid sinuses, and/or the medial portion of the maxillary sinus, with or without involvement of the nasal cavity. There must be no concurrent malignancy. |
| T3 | Tumor involving the lateral, inferior, superior, anterior, or posterior walls of the maxillary sinus, the sphenoid sinus, and/or the frontal sinus, with or without involvement of the medial portion of the maxillary sinus, the ethmoid sinuses, or the nasal cavity. There must be no concurrent malignancy. |
| T4 | All tumors with any extranasal/extrasinus extension to involve adjacent, contiguous structures, such as the orbit, the intracranial compartment, or the pterygomaxillary space. All tumors are associated with malignancy. |
Squamous Cell Carcinoma
SCC is the most frequent malignant tumor type, accounting for more than 60% of all sinonasal malignancies. The maxillary sinus and nasal cavity are the most common sites of origin, with peak incidence in the sixth and seventh decades. There is also a male-to-female predominance at 2:1 ratio. Multimodality therapy is the mainstay of treatment, depending on location and stage ( Table 4 ). Imaging’s main goal is to determine the extent of invasion, because SCC does not show specific CT or MRI findings ( Fig. 6 ). Overall prognosis is poor (<50% 5-year survival rate), worsened with involvement of neighboring structures or multiple subsites.
| Maxillary sinus | |
| T1 | Tumor limited to maxillary sinus mucosa with no erosion or destruction of bone |
| T2 | Tumor causing bone erosion or destruction, including extension into the hard palate and/or middle nasal meatus, except extension to posterior wall of the maxillary sinus and pterygoid plates |
| T3 | Tumor invades any of the following: bone of the posterior wall of the maxillary sinus, subcutaneous tissues, floor or medial wall of the orbit, pterygoid fossa, and ethmoid sinuses. |
| T4a |
|
| T4b |
|
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
