The vomeronasal organ: An objective anatomic analysis of its prevalence.

Abstract

The function and location of the vomeronasal organ in humans remains poorly understood. Indeed, there has been considerable controversy as to whether it even exists. Until now, there has been no published report of its prevalence or location as ascertained by the most widely accepted visual operative instrument in sinonasal surgery: the rigid nasal endoscope. In this study, multiple observers used the nasal endoscope to determine the prevalence and character of the vomeronasal organ in humans. We performed nasal endoscopy on 22 cadaver heads and 78 live humans; we also biopsied cadaver specimens to histologically confirm the endoscopic diagnosis. We found evidence of this organ in 13 of the 22 cadavers (59.1%) and in 22 of the 78 patients (28.2%). Many nasal surgeons are unaware of this organ and its potential physiologic significance. It is our hope that by recognizing its prevalence and location, nasal surgeons will be more likely to identify and possibly preserve this mysterious organ until its function is more clearly understood.

Introduction

The vomeronasal organ (VNO), also known as Jacobson's organ, is a part of the accessory olfactory system. It is an important component of the chemosensory apparatus of many vertebrate animals, but in adult humans it has been commonly regarded as rare and perhaps vestigial in nature. [1] Recently, however, the prevalence of this organ in adult humans was reported to be far greater than previously believed. Although the VNO has been reported in the human fetus, it was believed to degenerate before birth. [2] Several studies reported that the prevalence of VNOs ranges from 39 to 100%, but these studies were poorly controlled. [3-6]

The organ's function in animals has been extensively studied, but only recently has it been addressed in humans. Monti-Bloch et al determined that the VNO is a functional chemosensory organ in adult humans. [7] Electron microscopy and immunohistochemical studies show that its sensory epithelium has a characteristic ultrastructure and neuron pattern. [4,6,8]

Estimates of the prevalence of the VNO in humans vary widely, possibly because of the many different examination techniques that are used. The discrepancy might also be attributable to subjective examiner interpretation of this small and poorly defined structure. All previous studies of VNOs were based on the reported observation of a single clinician, and they do not take into account the possibility that there might have been a subjective bias. Moreover, the reproducibility of these previously reported subjective results is in question. For example, none included videotaped examinations that could be critically reviewed by multiple observers, and none used rigid endoscopes, which are an essential tool for any thorough nasal cavity examination.

Materials and methods

Cadaver study. The purpose of the cadaver investigation was to anatomically define the VNO. The nasal cavities of 22 fresh cadaver heads were videotaped through a rigid endoscope. When a possible VNO was identified, measurements were taken to document its location. Locations were measured posteriorly from a vertical line through the nasolabial angle to the center point of the suspected VNO. The vertical height was measured from the nasal floor to the center of the organ.

The cartilaginous nasal septum was then removed, and the possible VNO was carefully dissected and placed in a standard formalin solution. The tissue was then processed and stained with hematoxylin and eosin (H&E) dye. A structure was confirmed to be a VNO if there was a mucosal depression that significantly deepened toward the perichondrium (figure 1). These areas of depression were lined with mucosal cells similar to or flatter than the adjacent respiratory mucosa. The H&E-stained slides were evaluated microscopically and scored by both an otolaryngologist (J.W.) and a pathologist (R.C.) who were blinded to the results of the endoscopic examination. The scoring was based on a previously published microscopic description. [3]

Clinicalstudy. For this prospective observational study, we examined a consecutive sample of human subjects who were being seen in the otolaryngology clinic at Walter Reed Army Medical Center. After obtaining informed consent, one otolaryngologist (J.W.) examined each subject with a 30[degrees], 4-mm Hopkins rigid telescope attached to a camera and a videotape-recording device (figure 2). Each subject was prepared with a 0.25% phenylephrine topical decongestant solution that was sprayed into the nasal cavities.

After reviewing the completed data from the cadaver study, three of the authors (J.W., E.M., and W.B.) each evaluated the videotape separately and scored each subject for the presence of a VNO.

Results

Cadaver study. Many suspected VNOs that consisted of ellipsoid, thin, and pale or pigmented mucosa were biopsied and found on histology not to be VNOs. Histology provided a positive identification of only those specimens that had well-circumscribed pits with sharp borders and that were located medial to the anterior portion of the inferior turbinate, Based on these histologic criteria, we determined that six of the 22 cadavers (27.3%) had unilateral VNOs, seven (31.8%) had bilateral VNOs, and nine (40.9%) had no histologically confirmed VNO (table). None of the heads had more than one VNO per side.

We determined that the confirmed VNOs were located approximately 1.8 cm posterior to the nasolabial angle and 0.77 cm from the nasal floor (figure 3). This location corresponds anatomically to a position on the septum that is medial to the anterior portion of the inferior turbinate. This location was quite constant and correlated well with previously published locations. [3]

Clinical study. Eighty human subjects were examined, but two had large septal deviations that made it impossible to insert the endoscope for adequate visualization, and they were omitted from this study. Sixteen of the 78 (20.5%) had unilateral VNOs, six (7.7%) had bilateral VNOs, and 56(71.8%) had none (table). One patient had multiple VNOs on both sides. Of the 78 subjects, nine had had a previous septoplasty. Of these nine, only one had a unilateral VNO, while the remaining eight had no identifiable VNO. We noted no significant differences in VNO prevalence based on sex, age, or race.

Discussion

The cadaver portion of the study addressed the definition of the organ itself. The most consistent features were its location and its depression width. Potential VNOs that had medium to large depressions but no distinct borders and small lesions that had light brown pigmentation but no obvious depression turned out not to exhibit the histologic architecture of VNOs.

Light microscopy was used to histologically confirm a VNO according to the microarchitecture previously published (figure 1). [3] Using these methods, it would be possible to mistakenly miss a VNO only if (1) the structure of the VNO was different from what is described in the literature, (2) the VNO did not have a depression pit, or (3) the VNO was not visible on light microscopy.

The data from the cadaver portion of the study were used as a guide to score the VNOs in the human subjects. The three otolaryngologists independently determined the presence or absence of a VNO by viewing the videotaped examination. Those few examinations on which the observers did not agree were scrutinized and discussed by the three otolaryngologists collectively, and a consensus was eventually reached.

All of the previously published studies on VNOs were performed without the assistance of magnification or multiple observers. Without independent confirmation by multiple observers and without video documentation, the chance of inter- and intraobserver error increases. Perhaps other investigators considered small, flattened, hyper- or hypopigmented septal mucosa to be possible VNOs; we included only endoscopically discernible circumscribed pits in our anatomic assessments.

In conclusion, the VNO is a difficult structure to study because it is small and difficult to locate, even with the latest nasal endoscope technology. The great variation in its prevalence reported in earlier studies is a testament to this fact. In our study, we correlated endoscopic analysis of suspected cadaveric VNOs with microscopic histologic confirmation in order to define the endoscopic anatomic criteria of the VNO. The endoscope detects structures as small as 1 mm, while the microscope, of course, detects even smaller structures.

The prevalence of VNOs was higher in the cadavers than in the human subjects. One possible explanation for the difference is that we did not perform biopsies on living humans who had only marginally suspicious VNO criteria.

From both our cadaveric and human subject data, we can state with some confidence that the VNO does not exist in every human.

Acknowledgment

The authors acknowledge the contribution of statistician Robin S. Howard, MA.

From the Department of Otolaryngology--Head and Neck Surgery, Walter Reed Army Medical Center, Washington, D.C., and the National Naval Medical Center, Bethesda, Md. (Dr. Won); the Department of Otolaryngology--Head and Neck Surgery, Walter Reed Army Medical Center, Washington, D.C., and the Uniformed Services University of the Health Sciences, Bethesda, Md. (Dr. Mair); the Department of Otolaryngology--Head and Neck Surgery, University of Pennsylvania, Philadelphia (Dr. Bolger); and the Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, Md. (Dr. Conran).

References

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