Defining "True" Paranasal Sinuses: Histological Indicators of Secondary Pneumatization

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The recent use of computed tomography (CT) to study paranasal sinuses has resulted in a renewed focus on the phylogenetic significance and function of these mucosa-lined cranial cavities. However, identification of sinuses via CT is complicated because even mammals that lack true sinuses have concave regions (termed recesses) of the nasal cavity that can be mistaken for them. The difference is developmental; these recesses are simply the product of ossification of the cartilaginous nasal capsule, while true sinuses develop by a process known as pneumatization in which bone (and possibly cartilage) is actively removed by special cells (osteoclasts). To date, no study has documented the histological and cellular characteristics of these divergent processes, which lead to very different cranial shapes among species, and may well underlie developmental anomalies of clinical importance within mammalian species (including humans). In this project, the researchers will determine if microscopic distinctions exist between spaces that form identifiable paranasal sinuses versus the comparable natal recess in nonhuman primates. They will study cadaveric neonates of primates that do and do not develop maxillary and/or frontal sinuses, comparing such microanatomical aspects as hydroxyapatite density and patterns of tissue break-down in the nasal capsule walls, as well as bone remodelling activity in recesses and nascent sinuses. Microscopic examination of bone cells along the osseous boundaries of the sinuses/recesses will reveal the pattern of activity of bone removal (by osteoclasts) and bone deposition (by osteoblasts). Immunohistochemical methods with add greater scrutiny of osteoclast activity by identifying binding sites on bone as well as osteoclast precursor cells. This research tests the hypothesis that paranasal sinuses form via an invasive developmental trajectory that is distinct from routine bone remodeling.The researchers aim to draw a firm distinction between paranasal sinuses and recesses, and to more clearly understand the process which forms a "true" sinus - pneumatization. This research will contribute to the intellectual development of a graduate student, who will have the opportunity to assist in nearly every phase of the project. A digital archive of histological images from the specimens will be created and made available on the internet, providing a resource for other investigators of facial anatomy and ontogeny. The results of this research will serve as foundational knowledge to inform future work. Such information is needed to allow unambiguous identification of sinuses in any species, which will provide a firmer foundation for comparative CT studies and clinical research into sinus pathology. For example, the use of these spaces as phylogenetically important traits and the full understanding of certain congenital abnormalities of the facial skeleton (e.g., sinus absence and other abnormalities) hinge on a clear understanding of how sinuses form.