Abstract
Purpose
The aim of the study was to attract attention to the surgical significance of unilateral agenesis of the frontal sinus hidden by the overlapping expansion of the contralateral sinus toward the agenetic side.
Materials and methods
Retrospective review of endoscopic transnasal sinus dissections of 55 human cadavers (42, formalin fixated; 13, fresh frozen) was done in a tertiary care academic medical center. Surgical and radiologic findings were noted.
Results
Absence of right frontal sinus ostium in the presence of a connection between the right and left frontal sinuses was demonstrated in 2 (3.6%) cadavers. An absent and an incomplete septum between the frontal sinuses were also noted in these cadavers. No accompanying abnormality of other sinuses was found, and no evidence of previous sinus surgery was noted in these 2 cadavers.
Conclusions
If one of the frontal sinus ostia cannot be found during sinus surgery, although this sinus and its recess can be seen on the thick-sliced coronal computed tomographic (CT) scans, keep in mind that it may be (3.6%) an agenetic frontal sinus hidden by the extensive pneumatization of the contralateral sinus that is crossing the midline. It may not be possible to foresee this variant preoperatively by endoscopic examinations or thick-sliced CT scans. If there is suspicion, thin-sliced CT scans with reconstruction will be ideal to confirm the agenesis of the frontal sinus and to avoid complications. In the presence of such variant of frontal sinus, 1-sided successful frontal sinusotomy is adequate because this sinus or cell will already be drained through the treated frontal recess.
1
Introduction
The frontal sinus is located between the 2 layers of cortical bone in the anterior cranial vault. Its ostium or recess hides in a complex area that is covered by ethmoid cells. The close relationship between the frontal sinus and the anterior skull base or the orbit makes it vulnerable to surgical complications . A thorough knowledge of frontal sinus anatomy is crucial to avoid complications during frontal sinus surgery . Every endoscopic sinus surgeon should be aware of the complicated anatomy of the frontal sinus, as well as its abnormalities and variants that may exist. Also, it has been reported that the variations in the anatomy of frontal sinus may be critical for morphological or forensic investigations and for neurosurgeons performing pterional or supraorbital craniotomy .
Bilateral and unilateral aplasia or hypoplasia of the frontal sinus are not rare in the literature . Race, sex, geography, and climate have been implicated in the abnormal development of the frontal sinus . Absence of the frontal sinus has been noticed to have surgical and forensic significance . The frequency of bilateral absence of the frontal sinus has been reported in 3.4% to 10% of several populations . This frequency was significantly higher in the Alaskan (25%) and Canadian (43%) Eskimos . Unilateral absence of frontal sinus has been noticed to range from 0.8% to 7.4% .
During a primary endoscopic sinus surgery, we could not find the right frontal sinus ostia, although the right frontal recess and sinus were seen on the thick-sliced coronal computed tomographic (CT) scan. We, therefore, drilled and opened an artificial ostium at the safe point that was determined via computer-assisted image guidance. In this case, we have suspected and then became interested in the unilateral frontal sinus agenesis with expansion of the contralateral sinus to mimic the presence of bilateral frontal sinuses. The purpose of this study was to attract attention to the surgical significance of hidden unilateral agenesis of the frontal sinus. The technique of endoscopic sinus surgery and the detailed anatomy of the frontal recess were not the subjects of this study.
2
Materials and methods
In our institution, we perform endoscopic sinus dissections of 6 formalin-fixated cadavers and a few fresh-frozen cadavers annually in cooperation with the anatomy department of our university. The number of fresh-frozen cadavers varies per year depending on the availability of these cadavers. In addition, we get CT scans of fresh-frozen cadavers. These cadaver dissections are recorded into either videotapes or miniDVs, and all these records with the CT scans are stored by the senior author (BK). After the dissections, anatomical variations, abnormal, or interesting findings that are found during the dissections or on the CT scans and any evidence of previous sinonasal or craniofacial surgery were briefly noted. We retrospectively reviewed the records of cadavers that were endoscopically dissected between 2000 and 2006.
2
Materials and methods
In our institution, we perform endoscopic sinus dissections of 6 formalin-fixated cadavers and a few fresh-frozen cadavers annually in cooperation with the anatomy department of our university. The number of fresh-frozen cadavers varies per year depending on the availability of these cadavers. In addition, we get CT scans of fresh-frozen cadavers. These cadaver dissections are recorded into either videotapes or miniDVs, and all these records with the CT scans are stored by the senior author (BK). After the dissections, anatomical variations, abnormal, or interesting findings that are found during the dissections or on the CT scans and any evidence of previous sinonasal or craniofacial surgery were briefly noted. We retrospectively reviewed the records of cadavers that were endoscopically dissected between 2000 and 2006.
3
Results
Records of 55 cadavers (42 formalin fixated; 13 fresh frozen) were reviewed in this study. We had only coronal CT scans of 7 of the 13 fresh-frozen cadavers and only axial CT scans of the remaining 6 cadavers. None of the formalin-fixated cadavers was examined by CT. Moreover, optimum quality and ideal thickness of cross sections of CT were not available, and reconstructions of CT scans were not done.
Absence of right frontal sinus ostium in the presence of a connection between the right and left frontal sinuses was demonstrated in 2 (3.6%) of 55 cadavers. An absent and an incomplete septum between the frontal sinuses were noticed in these cadavers. No accompanying abnormalities of other sinonasal structures and no evidence of previous sinonasal surgery were noted for these 2 cadavers.
Case 1 involved a formalin-fixated male cadaver. Ostium of the right frontal sinus could not be found. The frontal recess was dissected, and the frontal sinus ostium was found easily at left side. Subsequently, both frontal sinuses were endoscopically visualized through the holes that were opened on the forehead of the cadaver at each side of the midline. The right frontal sinus was little bit smaller than the left one and had no ostium or recess. It was connected to the left one because there was no intersinus septum ( Fig. 1 A ). The left frontal sinus was connected to the nasal cavity through a recess ( Fig. 1 B). This connection was confirmed by a Kirschner’s wire that was inserted to the upper end of this recess and seen at the middle nasal meatus. Further external intervention was not permitted for this cadaver because of legal enforcements in our country.
