The majority of lesions that involve the anterior cranial base are tumors arising in the sinonasal cavity and which cause symptoms associated with their site of origin, although the signs may be quite nonspecific or subtle and therefore not appreciated until significant

FIGURE 12-1. Coronal CT scan demonstrating anatomy of anterior base of skull as well as a right ethmoid sinus squamous cell carcinoma.

tumor growth and extension have occurred. In particular, a careful medical history is often able to elicit nasal obstruction, epistaxis, anosmia/hyposmia, facial pain, or minor visual changes.5 A head and neck physical examination that includes anterior rhinoscopy and nasal endoscopy may demonstrate a lesion in the sinonasal cavity. CT and MR radiographs are critical in the diagnostic evaluation of anterior skull base lesions as well. In most cases, these studies are complementary in accurately defining a tumor's extent and its relationship to bony and soft tissue structures.

The pathologic diagnosis of lesions of the anterior skull base can be obtained, particularly when a significant intranasal tumor mass is present, via an office biopsy under local anesthesia. However, prudence must be exercised when performing a biopsy if a lesion appears vascular or if it is located in the superior nasal vault and its potential connection with the anterior cranial fossa could precipitate a cere-brospinal fluid (CSF) leak.

Lesions that involve or extend to the anterior skull base include a range of both benign and malignant histologies. While benign tumors including inverting papilloma (schneiderian papilloma), and juvenile nasopharyngeal angiofibroma (JNA) can require craniofacial approaches for surgical resection, the majority of tumors of the anterior skull base are malignant and include: adenocarcinomas and adenoid cystic carcinomas arising from the minor salivary glands of the sinonasal tract, squamous carcinomas arising from either the sinonasal cavity or the nasopharynx, chondrosarcomas or osteogenic sarcomas arising from the various bony and cartilaginous elements of the sinonasal cavity, soft tissue sarcomas, mucosal melanomas, esthesioneuroblastomas, and extensive skin cancers of the midface with deep penetration and skull base extension. Additionally, lymphomas (particularly in patients with human immunodeficiency virus [HIV]) and small cell neuroendocrine carcinomas may involve the anterior skull base although their treatment is generally non-surgical. While there are significant differences in the prognoses associated with these tumor types (as well as the need for adjuvant therapy), their surgical treatments do not significantly differ and they will therefore be discussed as a group. The differences in the biologic behavior of these various malignant his tologies will become more apparent when treatment results are discussed.

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