Fig. 3.1
External DCR intraoperative view of lacrimal sac fossa in an Asian patient. Suction tip points to the area of lacrimal bone suture line. The thick maxillary bony portion and anterior crest of the fossa lie above it. In this case, the maxillary bone is 2.5–3 times the width of the suction tip
In 69 lacrimal bones from 48 Finnish patients, Hartikainen et al. found the mean lacrimal bone thickness to be 106 μm, leading him to conclude that the lacrimal bone at the lacrimal sac fossa is so thin that it is easily penetrated in most cases [12]. However, Lui et al. measured lacrimal bone thickness in 386 Taiwanese patients during DCR and found the average thickness to be 5.8 ± 0.9 mm in males, and 4.2 ± 0.8 mm in females [13].
Anticipation of lacrimal and maxillary bone thickness by the lacrimal surgeon is important in selection of surgical approach. Adequate bony opening is critical in achieving surgical success. Paper-thin lacrimal bones easily lend themselves to large osteotomies with routine instruments, whereas achieving an adequate osteotomy in thick bone is more challenging and may require additional instrumentation, such as a drill. Selection of either an external or endoscopic approach to DCR should take into account anticipated lacrimal bone thickness.
Disease state itself may alter bone thickness. Hinton et al. found evidence of active bone remodeling in 19 % of bone pieces harvested from DCRs and conjunctivodacryocystorhinostomies [14]. Additionally, lacrimal bone thickness and density have been found to correlate with systemic bone density, suggesting that low-density, thin lacrimal bone may be found during DCR in patients with osteoporosis [15]. Osteoporosis is more common in women than men, and this may contribute to the clinical experience of easier osteotomies in women than men [16, 17].
Lacrimal Sac Fossa Relationship to Ethmoidal Sinus
In 1964, Zhang and Lui undertook detailed measurements of 100 Chinese orbits and lacrimal fossas. In 56 % of the specimens, they found ethmoidal air cell extension into the lacrimal sac fossa [18]. In 76 % of the specimens, the anterior portion of the middle turbinate was also encountered in this area. An intervening ethmoid sinus between the lacrimal sac and the nose may cause confusion when performing a DCR leading to an inadequate or false passage. Ethmoid sinus mucosa can be differentiated from nasal mucosa by being much thinner. Entering the anterior portion of the middle turbinate surgically may cause excessive bleeding, and partial blockage of the ostium by the middle turbinate may lead to obstruction. Lui suggests that such variations in nasal and lacrimal anatomy may account for the perceived difficulty of performing lacrimal surgery on Asian patients [13]. However, initial entry into the ethmoid air cells rather than the nasal cavity was described in 23 of 50 DCRs (46 %) by Talks of the United Kingdom in a presumably predominately white population [19]. Therefore, it behooves the lacrimal surgeon to understand the possible variations of nasal anatomy during all cases.
Lacrimal Sac Fossa Relationship to Cribriform Plate
Another surgically pertinent, possible difference between Whites and Asians is the location of the cribriform plate with respect to the lacrimal apparatus. Botek and Goldberg, in a dissection of five human cadaver heads, found the distance between the internal common punctum and the cribriform plate to be 25.1 ± 2.95 mm [20]. Neuhaus and Baylis performed DCRs and anatomic dissections on 3 fresh cadavers and found that the distance from a 15-mm vertical and 18-mm horizontal osteotomy to the floor of the anterior cranial fossa was 5.0 mm (range 1–7 mm) [21]. In a cadaver study of 28 Japanese skulls, Kurihashi and Yamashita measured the distance from a point 10 mm posterior to the medial canthus superiorly to the anterior cranial fossa floor. Although the distance ranged from 1 to 30 mm, with an average of 8.3 mm, 21 % had a distance of 3 mm or less. They recommended that surgeons not make a bony ostomy beneath the medial canthal tendon because of the possibility of violation of the cribriform plate [22].
Lacrimal Region Variations: Soft Tissue
External differences exist in the lacrimal region of Whites, Asians, and Blacks, particularly the absence or presence of epicanthal folds, the broad nasal bridge, and the thickness of the skin. Placement of skin incisions for an external DCR must take these factors into consideration. In a patient with a broad nasal bridge, the incision is more visible from a frontal view than in a patient with a prominent nasal bridge. Precise placement of the angle and length of the incision, particularly if a bilateral procedure is being performed, is essential for proper postoperative patient cosmesis. In patients with thicker skin of the nasal bridge, the incision should be placed closer to the medial canthus where thinner skin will more likely hide the scar. However, the epicanthal fold of some Asians must be avoided at all costs to prevent medial canthal webbing with scar contracture. An endoscopic DCR would avoid any potential problems arising from these external differences; however, one would need to take the thicker bone of the lacrimal region, often encountered in Asians and Blacks, into consideration.
Conclusion
In summary, some morphologic differences between the nasolacrimal systems of males and females and of different races have been well documented. Variations in anatomy also exist within each gender and race. These variations may or may not play a role in predisposition to disease, but they can play a role in surgical outcomes. The key to being a successful lacrimal surgeon lies in the awareness of such nuances and the ability to adjust surgical technique when an anatomic variation is encountered in any patient. Future comparative studies are needed to fully address such anatomic differences and provide better surgical guidelines.
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