Where is the ostium of the ethmoid bulla?

The natural ostium of the maxillary sinus opens into the floor of the ethmoid infundibulum. The ostium of the sphenoid sinus is in the sphenoethmoid recess, and the ostium of the posterior ethmoid sinus is in the superior meatus. The frontal sinus ostium opens into an hourglassshaped cleft, which is the frontal recess. Thanks to the remarkable advances in endoscopic surgical techniques and optical technology today, these ostia can be easily visualized. However, the ostium of the ethmoid bulla (the anterior ethmoid sinus) is usually difficult to locate, even with the use of a telescope.

The ethmoid bulla, a rounded projection of the lateral wall of the middle meatus, is the largest and most constant anterior ethmoid air cell. According to most textbooks, the drainage from the bulla opens into the middle meatus as part of the anterior ethmoid complex. But where in the middle meatus? Hollinshead, in his authoritative and widely read text of surgical anatomy of the head and neck, divides the anterior ethmoid cells into three groups: 1) the frontal recess cells, which open into the frontal recess of the middle meatus, 2) the infundibular cells, which open into the ethmoid infundibulum, and 3) the bullar (middle ethmoid) cells, which open directly into the middle meatus, either on or above the ethmoid bulla. [1] Hechl, Setliff and Tschabitscher, in their excellent atlas of the endoscopic anatomy of the paranasal sinuses published in 1997, write "the most consistent drainage pattern is from the posterior and medial aspect of the bulla medially into the hiatus semilunaris posterior (superior), ant erior to the basal lamella." [2]

In this article, we present three cases in which the ostium of the ethmoid bulla was found endoscopically and confirmed surgically.

Case 1. A small round ostium was found in the inferolateral wall of the right ethmoid bulla (figure, A). The ostium was in the lower portion of the hiatus semilunaris inferior, which is the entrance to the ethmoid infundibulum. Initially, this was thought to represent an accessory ostium of the maxillary sinus in its posterior fontanelle, but probing during surgery confirmed that it arose from the ethmoid bulla.

Case 2. An ethmoid bulla ostium opened into the hiatus semilunaris superior (figure, B and C). The medial bulla wall was gently probed. The ostium was easily found in the posterosuperior portion of the medial wall of the bulla and opened into the hiatus semilunaris superior. Methylene blue (-0.3 cc) instilled into the bulla lumen gradually drained into the hiatus semilunaris superior through the patent bulla ostium.

Case 3. An ethmoid bulla ostium was found on the anterior bulla wall. The oval-shaped ostium was in the middle portion of the vertical cleft on the anterior wall of the left ethmoid bulla (figure, D).

The ethmoid bulla is an important landmark along the lateral nasal wall, a starting point for anterior ethmoidectomy. The accompanying images demonstrate the variability in appearance of not only the ethmoid bulla, but the ostium as well. The variability in the configuration of the ethmoid bulla and its ostium is likely a result of the degree of pneumatization of the second ethmoid basal lamella during development. [3]

The ethmoid bulla ostia can be located on the lateral aspect of the bulla (hiatus semilunaris inferior), on the superior aspect of the bulla (suprabullar/retrobullar recess), or on the anterior face of the bulla. The ostium can be found in the posterior and medial aspect of the bulla (hiatus semilunaris superior), as mentioned by Hechl et al (figure, B). [2] In our experience, the opening into the hiatus semilunaris superior is not always easy to locate and can often be found convincingly only after the anterior wall of the ethmoid bulla is carefully removed and the opening is gently probed with a ball-tipped Lusk seeker. Care should be taken not to break the thin medial bulla wall and thereby create a false passage.

The ostium can be more accurately identified by observing mucociliary transport. However, observing mucociliary transport within the ethmoid sinus is more difficult than doing so within the maxillary sinus. Mucociliary flow can also be confirmed by instilling a small amount of dye, such as methylene blue (figure, C).

In summary, the ostium of the ethmoid bulla is often found in the hiatus semilunaris superior, but it can also be found in the anterior or lateral bulla wall, the ethmoid infundibulum, the hiatus semilunaris inferior, and the retrobullar recesses.

From the Southern New England Ear, Nose, Throat, and Facial Plastic Surgery Group and the Hospital of St. Raphael, New Haven, Conn. (Dr. Yanagisawa); the Section of Otolaryngology, Yale University School of Medicine, New Haven (Dr. Yanagisawa and Dr. Joe); and the Department of Otolaryngology, University of South Florida College of Medicine, Tampa (Dr. Christmas).

References

(1.) Hollinshead WH. Anatomy for Surgeons: The Head and Neck. 3rd ed. Philadelphia: J.B. Lippincott, 1982.

(2.) Hechl PS, Setliff RC, Tschabitscher M. Endoscopic Anatomy of the Paranasal Sinuses. New York: Springer, 1997.

(3.) Stammberger HR. Functional Endoscopic Sinus Surgery: The Messerklinger Technique. Philadelphia: B.C. Decker, 1991.