Anatomy

The tear film drains to the nasal cavities through the nasolacrimal system. Once produced by the lacrimal gland in the superior lateral lid, the tears flow medially and drain through the inferior and superior puncta, which are minute orifices, approximately 0.3 mm in diameter, located in the medial most aspect of the upper and lower lid. These orifices quickly narrow to form the superior and inferior canaliculus, which travel vertically, in the superior and inferior direction respectively for about 2 mm, and then turn 90° medially, extending for approximately 8 mm within the fibers of the orbicularis oculi muscle.

In approximately 90% of the people, the horizontal portion of the superior and inferior canaliculus merge into the common canaliculus that drains into the lacrimal sac. The lacrimal sac lies in the lacrimal fossa, which is a depression in the anteromedial aspect of the bony orbit at the junction of the frontal process of the maxilla anteriorly and the lacrimal bone posteriorly. The lacrimal sac is approximately 10 to 15 mm in vertical height and continues inferiorly as the nasolacrimal duct. The duct resides in a bony canal that is composed by the maxilla anteriorly and the lacrimal bone posteriorly and terminates in the inferior meatus as the valve of Hasner, located approximately 35 mm posterior to the insertion of the inferior turbinate head. Endonasally, the nasolacrimal system corresponds to the maxillary line, which is the curvilinear eminence that projects from the anterior attachment of the middle turbinate superiorly to the root of the inferior turbinate inferiorly ( Fig. 1 ).

Endoscopic appearance of the left maxillary line. The maxillary line is found running in a curvilinear fashion along the lateral nasal wall from the insertion of the middle turbinate (MT) superiorly to the insertion of the inferior turbinate. In this view of the left nasal cavity, the maxillary line is highlighted by the short arrows, whereas the free margin of the uncinate process (U) is demarcated by the diamonds. S, septum.

The lacrimal sac and duct have an intimate relationship with the structures on the lateral nasal wall. The uncinate process attaches to the lateral nasal wall at the suture between the maxilla and the lacrimal bone and extends posteriorly. Calhoun and colleagues found that the nasolacrimal duct and sac lie 1 to 8 mm anterior to the root of the uncinate process and that the distance from the natural ostium of the maxillary sinus to the lacrimal drainage system ranges from 0.5 to 18 mm. In this region, the lacrimal bone can be particularly thin, or even absent in 20% of individuals. Hartikainen and colleagues reported that the mean thickness of lacrimal bone was less than 100 μm, and that this thickness was greater than 300 μm in only 4% of patients.

Furthermore, the pneumatization of the agger nasi cell is variable and can extend anteriorly, pneumatizing the lacrimal bone and the frontal process of the maxilla in up to 54% of individuals. Under these circumstances, the bone overlying the nasolacrimal sac and duct can be thin, posing a risk for injury when dissecting on this area.

Prevention

Surgery of the osteomeatal complex begins with an uncinectomy. The best way to prevent LDI is to have a comprehensive understanding of the relationship of the duct to the uncinate process and anterior medial maxillary sinus.

Uncinectomy can be performed using several techniques. The anterior to posterior approach uses a sickle knife to incise along the maxillary line in a posterolateral trajectory, liberating the uncinate from its attachment and exposing the infundibulum. The uncinate is then grasped with a Blakesley forceps and rotated medially/inferiorly to remove the uncinate from the superior and then inferior attachments. If the initial incision is made anterior to the root of the uncinate, one can easily violate the duct.

The posterior to anterior approach for removing the uncinate process uses backbiting forceps. This procedure is performed in a retrograde manner, introducing the forceps in the middle meatus, turning the blade laterally, and inserting behind the free margin of the uncinate to rest in the infundibulum. The forceps is then closed and in this manner and the uncinate process is removed piecemeal from posterior to anterior. The dissection is terminated when the “hard bone” of the lacrimal bone is encountered. However, because in many individuals this bone is not always hard, but rather thin or absent, the surgeon cannot rely solely on “palpation of hard bone” to stop the dissection. At that point, an injury is likely to have already occurred.

One tool that can significantly improve visualization of this area is the angled endoscope. Using a 30° or 45° endoscope can help visualize the true ostia of the maxillary sinus and determine the limit of the anterior dissection. The authors advocate that the safest way to perform an uncinectomy and avoid LDI is to use the ball-tipped ostium seeker to palpate the infundibulum and fracture the uncinate medially, as initially described by Parsons and colleagues. At that point, the backbiting forceps is introduced in the inferior portion of the uncinate and used to remove the uncinate from the inferior attachment anteriorly to its root or until the maxillary ostium is visualized. An upbiting 90° Blakesley forceps is then introduced and, through a push–pull maneuver, the superior and anterior attachments are disrupted and the uncinate removed. Alternatively, once the uncinate process has been delivered medially with the ball-tipped seeker, a microdebrider can be used to remove the freed component of the uncinate, taking care to remove the retained attachments with either a backbiting forceps or the 90° Blakesley forceps.

The proximity of the natural ostia to the nasolacrimal duct should also be appreciated. Thus, when enlargement of the natural ostium is clinically indicated, one should only enlarge toward the posterior fontanelle, leaving the natural anterior margin of the anterior fontanelle, as the anterior limit of the surgical antrostomy. If using the backbiting forceps to enlarge anteriorly, one can easily injure the nasolacrimal duct. Thus, by enlarging the ostia only posteriorly, not only is an intact rim of mucosa preserved, minimizing the degree of postsurgical stenosis, but also injury to the duct can be avoided.

Prevention

Surgery of the osteomeatal complex begins with an uncinectomy. The best way to prevent LDI is to have a comprehensive understanding of the relationship of the duct to the uncinate process and anterior medial maxillary sinus.

Uncinectomy can be performed using several techniques. The anterior to posterior approach uses a sickle knife to incise along the maxillary line in a posterolateral trajectory, liberating the uncinate from its attachment and exposing the infundibulum. The uncinate is then grasped with a Blakesley forceps and rotated medially/inferiorly to remove the uncinate from the superior and then inferior attachments. If the initial incision is made anterior to the root of the uncinate, one can easily violate the duct.

The posterior to anterior approach for removing the uncinate process uses backbiting forceps. This procedure is performed in a retrograde manner, introducing the forceps in the middle meatus, turning the blade laterally, and inserting behind the free margin of the uncinate to rest in the infundibulum. The forceps is then closed and in this manner and the uncinate process is removed piecemeal from posterior to anterior. The dissection is terminated when the “hard bone” of the lacrimal bone is encountered. However, because in many individuals this bone is not always hard, but rather thin or absent, the surgeon cannot rely solely on “palpation of hard bone” to stop the dissection. At that point, an injury is likely to have already occurred.

One tool that can significantly improve visualization of this area is the angled endoscope. Using a 30° or 45° endoscope can help visualize the true ostia of the maxillary sinus and determine the limit of the anterior dissection. The authors advocate that the safest way to perform an uncinectomy and avoid LDI is to use the ball-tipped ostium seeker to palpate the infundibulum and fracture the uncinate medially, as initially described by Parsons and colleagues. At that point, the backbiting forceps is introduced in the inferior portion of the uncinate and used to remove the uncinate from the inferior attachment anteriorly to its root or until the maxillary ostium is visualized. An upbiting 90° Blakesley forceps is then introduced and, through a push–pull maneuver, the superior and anterior attachments are disrupted and the uncinate removed. Alternatively, once the uncinate process has been delivered medially with the ball-tipped seeker, a microdebrider can be used to remove the freed component of the uncinate, taking care to remove the retained attachments with either a backbiting forceps or the 90° Blakesley forceps.

The proximity of the natural ostia to the nasolacrimal duct should also be appreciated. Thus, when enlargement of the natural ostium is clinically indicated, one should only enlarge toward the posterior fontanelle, leaving the natural anterior margin of the anterior fontanelle, as the anterior limit of the surgical antrostomy. If using the backbiting forceps to enlarge anteriorly, one can easily injure the nasolacrimal duct. Thus, by enlarging the ostia only posteriorly, not only is an intact rim of mucosa preserved, minimizing the degree of postsurgical stenosis, but also injury to the duct can be avoided.