The Development and Pathologic Processes that Influence Maxillary Sinus Pneumatization

The maxillary sinus is universally described as a pyramidal-shaped cavity in the maxilla. Hypoplasia, which can occur unilaterally or bilaterally, is graded by the authors by the degree of failure of descent below the nasal floor in achieving its position adjacent to the posterior dentition in the adult. Unlike early studies using plain X-rays, which considered pneumatization into the zygomatic recess and dental alveolus as criteria, the authors have adopted the above-cited parameters based on computed tomography (CT) imaging, which reveals that even when smaller the sinus retains a pyramidal configuration, although truncated. Rarely, the sinus is excessively pneumatized in the nonpathologic state. Review of the literature failed to reveal a comprehensive study of the conditions that alter maxillary sinus volume and configuration. Based on a retrospective review of 6,000 high resolution CT scans of the paranasal sinuses, the types and relative incidences of these conditions have been determined, and a classification system proposed. The mixed-sex sample group (= 2,540) was comprised of nonpediatric (adolescent and adult) and was of a polyethnic composition. Results showed that enlargement of the sinus is uncommonly encountered, and is produced by air (pneumocele) and mucus (mucocele) entrapment, or by benign tumors which have arisen in the sinus or adjacent maxilla and have grown intracavitarily, with the sinus walls expanding and remodeling to accommodate them. Reduction in size and volume is more frequent. Heredo-familial syndromic conditions reduce sinus size by impaired facial growth centers, or obliteration by dense osteosclerosis. Irradiation for neoplastic disease in the pediatric population similarly, directly effect growth centers, or impairs pituitary function. Another iatrogenic cause, direct surgical intervention (Caldwell-Luc procedure) almost universally alters sinus volume and shape by osteoneogenesis. Midfacial fractures involving the sinus also produce distortion by sclerosis as well as by malpositioning of bone fragments. The principal systemic disorders, sickle cell anemia and osteopetrosis, which diffusely effect medullary bone, do so either through compensatory marrow proliferation or sclerotic new bone formation, thus serving to produce maxillary enlargement and sinus obliteration. The greatest source of maxillary sinus distortion and destruction are neoplasms. Malignant sinonasal and oral cavity tumors produce bony erosion of the sinus walls, whereas benign odontogenic cysts remain external to the sinuses and compress it as they enlarge. Most odontogenic tumors produce external compression and remodeling. Fibro-osseous disorders similarly produce size and shape distortions by external impingement. Although diverse developmental and pathological conditions influence maxillary sinus morphology, there is a limited range of biologic response.