The Frontal Sinus and Frontal Recess: Anatomical, Radiological and Surgical Concepts

THIEME 364 Update Article The Frontal Sinus and Frontal Recess: Anatomical, Radiological and Surgical Concepts Camila S. Dassi1,2 Flávia R. Demarco1,2 João Mangussi-Gomes1,2 Leonardo Balsalobre1,2 Aldo C. Stamm1,2 1 São Paulo Skull Base Center, São Paulo, SP, Brazil 2 São Paulo Ear, Nose, and Throat Center, Hospital Edmundo Vasconcelos, São Paulo, SP, Brazil Raimar Weber2 Address for correspondence Aldo C. Stamm, MD, PhD, Rua Afonso Braz, 525, Cj 13, São Paulo 04511-011, Brazil (e-mail: ). Int Arch Otorhinolaryngol 2020;24 (3) :364–375. Abstract Keywords ► frontal sinus ► frontal recess ► frontal sinus drainage pathway ► endoscopic sinus surgery ► draf classification ► modified lothrop procedure Introduction The frontal sinus (FS) is the most complex of the paranasal sinuses due to its location, anatomical variations and multiple clinical presentations. The surgical management of the FS and of the frontal recess (FR) is technically challenging, and a complete understanding of its anatomy, radiology, main diseases and surgical techniques is crucial to achieve therapeutic success. Objectives To review the FS and FR anatomy, radiology, and surgical techniques. Data Synthesis The FS features a variety of anatomical, volumetric and dimensional characteristics. From the endoscopic point of view, the FR is the point of greatest narrowing and, to have access to this region, one must know the anatomical limits and the ethmoid cells that are located around the FR and very often block the sinus drainage. Benign diseases such as chronic rhinosinusitis (CRS), mucocele and osteomas are the main pathologies found in the FS; however, there is a wide variety of malignant tumors that can also affect this region and represent a major technical challenge to the surgeon. With the advances in the endoscopic technique, the vast majority of diseases that affect the FS can be treated according to Wolfgang Draf, who systemized the approaches into four types (I, IIa, IIb, III). Conclusion Both benign and malignant diseases that affect the FS and FR can be successfully managed if one has a thorough understanding of the FS and FR anatomy, an individualized approach of the best surgical technique in each case, and the appropriate tools to operate in this region. Introduction Surgical management of the frontal sinus (FS) is considered the most difficult and challenging part of endoscopic sinus surgery. The idiosyncrasies of the frontal sinus drainage pathway (FSDP) anatomy and its intimate proximity to the orbit and skull base may lead the surgeon to its inadequate dissection and consequently expose the patient to major complications. Meticulous anatomical knowledge of this region and proper surgical planning that starts before the patient enters the received April 24, 2020 accepted May 10, 2020 DOI https://doi.org/ 10.1055/s-0040-1713923. ISSN 1809-9777. operating room is mandatory for any otolaryngologist to perform a safe and successful surgery. This paper will provide a comprehensive overview of the most useful concepts and techniques regarding frontal sinus surgery. Anatomical and Radiological Considerations Similarly, as with any surgery, a thorough anatomical knowledge is the key part of a successful surgical procedure. Due to the proximity of the FS to the orbit and skull base, special care must be taken during endoscopic sinus surgery of the FS.1 The Copyright © 2020 by Thieme Revinter Publicações Ltda, Rio de Janeiro, Brazil The Frontal Sinus and Frontal Recess: Anatomical, Radiological and Surgical Concepts FS is an air space located in the anterior cranial vault and is surrounded by two walls of cortical bone. Previous studies referred to the FS as a ‘‘large ethmoid air cell” given the common embryological and anatomical relationships between the FS and the ethmoid sinus.2,3 The two theories of embryological origin are that the FS develops as a result of direct expansion of the infundibulum and frontonasal recess, or as an ascending epithelial migration of the anterior ethmoid cells that infiltrate the frontal bone between its 2 walls during the 16th week. The FS begins as an insignificant pneumatization in the newborn and becomes radiographically visible around the age of 4 years old. Craniofacial growth is synchronous with the FS and its peak expansion occurs at
18 years old.4 The FS has great anatomical, volumetric and dimensional variability and can reach enormous proportions, with projections into the zygomatic, supraorbital recesses and parietal bones. Unilateral or bilateral FS aplasia is seen in between 3 and 5% of individuals.4 Anatomical understanding of the frontal sinus drainage pathway (FSDP) complex, specially the frontal recess (FR), is twofold for a favorable surgical outcome. Dassi et al. Resembling an hourglass shape, the FSDP is formed by the frontal ostium superiorly and the FR inferiorly.2,5 Described as a connection between the FS and the anterior ethmoid cells, the FR is an inverted, cone-shaped space with the superior narrow end at the internal frontal ostium. The lower limit is wider than the superior one and blends into the anterior ethmoid cells.6 The agger nasi cell (ANC) and frontal beak forms the anterior limit of the FR, while the posterior limit consists of the ethmoid bulla and skull base. The medial wall of the orbit and lacrimal bone lies lateral to the FR, and the vertical portion of the middle turbinate forms its medial limit.7,8 Anatomical variations of the inferior third of the FSDP are the main source of obstruction and resulting FS disease (►Fig. 1). The ANC is the most anterior ethmoid cell, marking the anterior limits of the FR, and is therefore used as a reference point for accessing the FS. The extent of pneumatization of the ANC rather than the number or site of cells better determines the endoscopic accessibility to the FS.9 The union of its medial wall with the uncinate process (UP) forms the “vertical bar”, which is a useful landmark to achieve a correct identification of the FR and FS (►Fig. 2).10 Usually, the ANC Fig. 1 Coronal sections (A-D) computed tomography scan depicting the anatomy of the frontal sinus drainage pathway and surrounding structures. ANC ¼ agger nasi cell; RFS ¼ right frontal sinus; white dotted line ¼ frontal sinus drainage pathway; ISS ¼ intersinus septum; IT ¼ inferior turbinate; LFS ¼ left frontal sinus; Max ¼ maxillary sinus; MT ¼ middle turbinate; S ¼ nasal septum; HC ¼ haller cell; UP ¼ uncinate process. International Archives of Otorhinolaryngology Vol. 24 No. 3/2020 365 366 The Frontal Sinus and Frontal Recess: Anatomical, Radiological and Surgical Concepts Dassi et al. Fig. 2 Endoscopic anatomy of the left frontal recess. Uncinate process (1), vertical bar (2), agger nasi (3), frontal sinus drainage pathway (4) and ethmoidal bulla (5). Fig. 3 Endoscopic anatomy of the left anterior ethmoid artery and its relations. Anterior ethmoid artery (arrow), left frontal sinus (1), skull bas (...truncated)