Key points

Introduction

Paranasal sinus and skull base malignancies include a heterogeneous group of tumors with widely varying histology and prognosis. Because of typically late presentation and the frequent involvement of critical structures, including the orbit and brain, these tumors represent a great challenge for head and neck surgeons and oncologists.

Perhaps adding to this complexity is that paranasal sinus malignancies remain an uncommon and rare entity in Western countries. The incidence of these cancers is estimated to be less than 1 per 100,000 individuals per year, and they represent only a small fraction of the total number of head and neck cancers. Most of these cancers are located in either the maxillary sinus or nasal cavity, with cancers of other sinuses occurring more infrequently. Although varied based on specific tumor histology, these cancers are most frequently diagnosed during or after the sixth decade of life. These neoplasms also have unique risk factors. Contributing factors for other head and neck cancers, such as tobacco use, alcohol abuse, and human papillomavirus, do not seem to be strongly correlated with these tumors. Instead, occupational hazards and long-term inhalation of industrial toxins have historically been linked to the development of paranasal sinus malignancies, possibly by promoting chronic inflammation. Specifically, workers in the furniture, textile, and leather industries have been shown to be at increased risk.

Although often discussed as a group because of their rarity, paranasal sinus and ventral skull base malignancies include more than 40 unique histologies ( Box 1 ), as classified by the World Health Organization. These etiologies are broadly subclassified into epithelial or nonepithelial malignancies. Squamous cell carcinoma (SCC), adenocarcinoma, and sinonasal undifferentiated carcinoma (SNUC) are common epithelial pathologies, whereas rhabdomyosarcoma and lymphomas are well-known nonepithelial tumors that occur in this region. Overall, SCC has been reported to be the most common of these histologies and comprises between 36% and 58% of all paranasal sinus cancers, followed in frequency by adenocarcinoma, mucosal melanoma, esthesioneuroblastoma (ENB), and adenoid cystic carcinoma.

Introduction

Paranasal sinus and skull base malignancies include a heterogeneous group of tumors with widely varying histology and prognosis. Because of typically late presentation and the frequent involvement of critical structures, including the orbit and brain, these tumors represent a great challenge for head and neck surgeons and oncologists.

Perhaps adding to this complexity is that paranasal sinus malignancies remain an uncommon and rare entity in Western countries. The incidence of these cancers is estimated to be less than 1 per 100,000 individuals per year, and they represent only a small fraction of the total number of head and neck cancers. Most of these cancers are located in either the maxillary sinus or nasal cavity, with cancers of other sinuses occurring more infrequently. Although varied based on specific tumor histology, these cancers are most frequently diagnosed during or after the sixth decade of life. These neoplasms also have unique risk factors. Contributing factors for other head and neck cancers, such as tobacco use, alcohol abuse, and human papillomavirus, do not seem to be strongly correlated with these tumors. Instead, occupational hazards and long-term inhalation of industrial toxins have historically been linked to the development of paranasal sinus malignancies, possibly by promoting chronic inflammation. Specifically, workers in the furniture, textile, and leather industries have been shown to be at increased risk.

Although often discussed as a group because of their rarity, paranasal sinus and ventral skull base malignancies include more than 40 unique histologies ( Box 1 ), as classified by the World Health Organization. These etiologies are broadly subclassified into epithelial or nonepithelial malignancies. Squamous cell carcinoma (SCC), adenocarcinoma, and sinonasal undifferentiated carcinoma (SNUC) are common epithelial pathologies, whereas rhabdomyosarcoma and lymphomas are well-known nonepithelial tumors that occur in this region. Overall, SCC has been reported to be the most common of these histologies and comprises between 36% and 58% of all paranasal sinus cancers, followed in frequency by adenocarcinoma, mucosal melanoma, esthesioneuroblastoma (ENB), and adenoid cystic carcinoma.

Staging

Because of this remarkably wide variety of histologies, the development of a comprehensive staging system with prognostic relevance for each tumor subtype and anatomic location has historically presented a unique challenge. The first major effort to elucidate prognostic variables was made by Ohngren in 1936. He proposed an imaginary line, now referred to as the Ohngren line, running from the angle of the mandible to the medial canthus. He described that lesions located anterior and/or inferior to this line seemed to have an improved prognosis and higher likelihood of complete resection. In contrast, tumors located posterior and/or superior to this line, including those of the frontal, ethmoid, and sphenoid sinus, were more difficult to resect and frequently involved high-value structures of the head and neck, thus portending an overall poorer prognosis.

Today, the paranasal sinuses and nasal cavity are incorporated into conventional TNM classifications by the American Joint Committee on Cancer (AJCC). This system is primarily structured by the extent of tumor invasion ( Table 1 ). Because of this focus on the involvement of specific structures rather than the total lesion size, the system features separate “T” classifications for maxillary tumors and nasal cavity/ethmoid tumors. Of note, this AJCC staging system does not include “T” staging for either sphenoid or frontal tumors. This TNM system is also used to further categorize these malignancies into stages I to IV for prognostic purposes. Using data from the National Cancer Data Base for patients diagnosed with any nasal or sinus malignancy in 1998 to 1999, the AJCC reported a relative 5-year survival rate of 63% for stage I tumors, 61% for stage II tumors, 50% for stage III, and only 35% for stage IV.

Unfortunately, because specific cancer pathology is a major determinant of survival and neck metastases are relatively uncommon for paranasal sinus and ventral skull base malignancies, this TNM classification system may not be as clinically useful for determining prognosis as comparable systems for other head and neck cancers. Because of this complexity, a variety of alternative or modified staging systems have been developed for specific tumor subtypes. This article reviews specific systems of staging for common sinonasal/ventral skull base pathologies and their utility in determining prognosis.