The frontal sinuses show the most anatomic variation such as congenital absence or hypoplasia (Fig. 1). The sphenoid sinuses, located posteriorly, form last. Anatomy of Sinuses-Artist's Rendition.

The nasal septum is very small, and the nostrils are shaped like a half-moon, comma, or triangle. The frontal sinuses are often missing. The nostrils may be triangular if the hypoplasia is severe.