Development of the Ethmoid Sinus and Extramural Migration: The Anatomical Basis of this Paranasal Sinus

Abstract

Frontal and/or maxillary sinusitis frequently originates with pathologic processes of the ethmoid sinuses. This clinical association is explained by the close anatomical relationship between the frontal and maxillary sinuses and the ethmoid sinus, since developmental trajectories place the ethmoid in a strategic central position within the nasal complex. The advent of optical endoscopes has permitted improved visualization of these spaces, leading to a renaissance in intranasal sinus surgery. Advancing patient care has consequently driven the need for the proper and accurate anatomical description of the paranasal sinuses, regrettably the continuing subject of persistent confusion and ambiguity in nomenclature and terminology. Developmental tracking of the pneumatization of the ethmoid and adjacent bones, and particularly of the extramural cells of the ethmoid, helps to explain the highly variable adult morphology of the ethmoid air sinus system. To fully understand the nature and underlying biology of this sinus system, multiple approaches were employed here. These include CT imaging of living humans (n 5 100), examination of dry cranial material (n 5 220), fresh tissue and cadaveric anatomical dissections (n 5 168), and three-dimensional volume rendering methods that allow digitizing of the spaces of the ethmoid sinus for graphical examination. Results show the ethmoid sinus to be highly variable in form and structure as well as in the quantity of air cells. The endochondral bony origin of the ethmoid sinuses leads to remarkably thin bony contours of their irregular and morphologically unique borders, making them substantially different from the other paranasal sinuses. These investigations allow development of a detailed anatomical template of this region based on observed patterns of morphological diversity, which can initially mask the underlying anatomy. For example, the frontal recess, ethmoid infundibulum, and hiatus semilunaris are key anatomical components of the ethmoid structural complex that are fully documented and explained here on the basis of the template we have developed, as well as being comprehensively illustrated. In addition, an exhaustive 2000-year literature search identified original sources of nomenclature, in order to help clarify the persistent confusions found in the literature. Modified anatomical terms are suggested to permit proper description of the ethmoid THE ANATOMICAL RECORD 291:1535-1553 (2008 region. This clarification of nomenclature will permit better communication in addition to eliminating redundant terminology. The combination of anatomical, evolutionary, and clinical perspectives provides an important strategy for gaining insight into the complexity of these sinuses.

Computed-tomography volumetric study of the ethmoid labyrinth

“…It originates from the cartilaginous nasal capsule (paleosinus), while the other paranasal sinuses will develop as extensions from the capsule (extracapsular migration) into the surrounding bones 7 .…”

“…Due to this important characteristic of ethmoid cells, it is said that one cell may outgrow the ones next to it and force them in another direction, or limit their expansion 7,8 . Different pneumatization and expansion types of the ethmoid make it a challenge to establish a certain pattern in its anatomy.…”

Paranasal Sinus Anatomy: What the Surgeon Needs to Know

“…The ostium of the ethmoid bulla often located on the upper margin of the posterior wall and drains into the middle meatus. Ethmoid bulla can be of variable sizes; however, occasionally "about 8% of the population," it might be underdeveloped [27].…”

CBCT Imaging of Paranasal Sinuses and Variations

“…Especially, extramural and intramural expansion of the ethmoid cells causes highly variable anatomy in the nasal complex [13]. These anatomic variations may contribute to the occurrence of the paranasal sinus disease or cause operative complications when performing sinus surgery.…”