Surg Radiol Anat (2011) 33:697–702 DOI 10.1007/s00276-011-0808-8

ORIGINAL ARTICLE

The neglected anatomical and clinical aspects of pterygoid canal: CT scan study Galal Omami • Gebril Hewaidi • Reji Mathew

Received: 23 August 2010 / Accepted: 15 March 2011 / Published online: 29 March 2011 Ó Springer-Verlag 2011

Abstract Purpose To present the variable positions of pterygoid canal (PC) relative to sphenoid sinus floor and cavity, which may be helpful for understanding pathologic and surgical conditions related to sphenoid sinus region. Materials and methods Coronal sinonasal CT images of 300 adult patients, in the Department of Radiology at AlJala Traumatology Hospital, Benghazi, Libya, were investigated for the positional variation and dehiscence of PC. Of the patients, there was equal gender distribution, ages ranged between 16 and 82 years (mean age 34.6 years). The position of PC was categorized as below the sinus floor, within the floor, and within the sinus cavity (protrusion). Results Canals located under the floor were identified in 38.3% (230/600), within-the-floor canals were encountered in 39.6% (238/600); and canals protruding into the sinus cavity (i.e., within sinus cavity) were observed in 22% (132/600). Dehiscence of the bony wall of PC was recognized in 26% (157/600). Coexistence of PR and protruding PC was found in 16.5% (99/600), 7.3% (44/600) on the right side and 9.2% (55) on the left side. Statistically, there was significant association between PR and PC protrusion (p = 0.000). Conclusion The anatomical and positional variations of PC are highly encountered. Surgeons addressing vidian G. Omami (&)
R. Mathew Oral and Maxillofacial Radiology, University of Connecticut School of Dental Medicine, 263 Farmington Avenue, Farmington, CT 06030, USA e-mail: [email protected] G. Hewaidi Department of Diagnostic Radiology, Al-Jala Traumatology Hospital, Benghazi, Libya

neurectomy must be familiar with the positional variations of PC in the preoperative CT images for easier and safer nerve identification and transection. Keywords Pterygoid canal
Vidian neurectomy
Sluder’s neuralgia
Sphenoid sinus

Introduction Pterygoid (Vidian) canal runs anteriorly from the anterior border of foramen lacerum, through the sphenoid sinus floor, to end in the pterygopalatine fossa [18]. It transmits pterygoid (Vidian) nerve and artery. Pterygoid nerve is an autonomic nerve formed by confluence of deep petrosal nerve (sympathetic; sympathetic carotid plexus) and greater superficial petrosal nerve (parasympethic; geniculate ganglion of facial nerve). It passes through pterygoid canal (PC) to synapse in the sphenopalatine (Meckel’s) ganglion. Postganglionic branches are distributed via branches of maxillary nerve to lacrimal gland, nasal and palatal mucosa (Fig. 1). Vasomotor rhinitis is a condition believed to result from a relative imbalance of parasympathetic to sympathetic stimulation of the blood vessels and glands of the nasal mucosa. It is characterized by symptoms of clear rhinorrhea and nasal congestion. Sluder’s neuralgia of the pterygopalatine ganglion is a rare disorder first described by Sluder in 1908, characterized by unilateral, severe, burning, boring or nagging headache, starting around the eye and the bridge of the nose, radiating to the maxilla and maxillary teeth, zygoma, mastoidal area and occiput, or even as down as the shoulder and arm [14]. Sluder’s neuralgia is sparsely reviewed in the literature and being classified as

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Fig. 1 Coronal diagram shows anatomy of sphenoid sinus region

synonymous with Vidian neuralgia [3, 19]. Crocodile tears syndrome (gustatory lacrimation; tearing on eating) is a rare complication of facial nerve lesion proximal to the geniculate ganglion; where regenerating preganglionic salivatory fibers intended for the chorda tympani nerve are misdirected to the sphenopalatine ganglion which project to the lacrimal gland [1]. Vidian neurectomy has been introduced into otolaryngology practice in early 1960s, involves surgical sectioning of pterygoid nerve [2]. Recently, there has been renewed interest in this procedure because understanding of the endoscopic anatomy had improved [5]. Vidian neurectomy is indicated for the treatment of vasomotor rhinitis [8], Sluder’s neuralgia [14], crocodile tears syndrome [1], allergic rhinitis (hay fever) [7], and nasal polyposis [16]. Moreover; it has been reported that protrusion or dehiscence of PC could render pterygoid nerve vulnerable in endoscopic manipulation of sphenoid sinus region [4]. Computerized tomography scan is the best tool to demonstrate paranasal sinuses [20]. Axial and coronal views are useful in delineating the anatomical landmarks of sinonasal cavity; however, coronal CT-scan provides most of the information required for endoscopic clearance [10]. The purpose of the study was to present the variable positions of PC relative to sphenoid sinus floor and cavity, which may be helpful for understanding pathologic and surgical conditions related to sphenoid sinus region.

Materials and methods Coronal sinonasal CT images of 300 adult patients were investigated for the anatomy of PC. All images were acquired by GE HiSpeed CT Scanner in the Department

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of Radiology at Al-Jala Traumatology Hospital, Benghazi, Libya. All CT examinations were requested for varying sinonasal, otologic and maxillofacial indications. For the reliability of the investigation, we excluded patients with prior sinus surgery, sinonasal polyposis, and patients younger than 16 years, as according to Gray, the extension of the nasal cavity into the body of the sphenoid bone, to form the sphenoid sinus, is present before birth and does not reach its full extension until adolescence [9]. Of the patients, there was equal gender distribution, ages ranged between 16 and 82 years (mean age 34.6 years). For the tomographic examination, the scanner gantry was angled perpendicular to the hard palate. 4-mm contiguous slices were taken from anterior frontal sinus to anterior sphenoid sinus, and 2-mm contiguous slices were used from anterior to posterior sphenoid sinus, for better evaluation of PC and its relation to the sinus floor. The position of PC was categorized as below the sinus floor, within the floor, and within the sinus cavity (protrusion). PC lies below the floor when it is separated from it by bone density; PC lies in the floor when the later roofs the canal; whereas the canal was regarded protruding into the sinus cavity when it is surrounded by some air density. Dehiscence of PC was defined as absence of visible bone density separating the sinus from the canal. In cases of not to obtain a clear decision between ‘‘very thin bony wall’’ and ‘‘total dehiscence’’, the results were accepted as dehiscence. Pterygoid recess (PR) was recognized when sinus pneumatization extends beyond a horizontal plane across PC’s. Chi-square test and contingency coefficient were used for statistical analysis of the obtained data and p \ 0.01 was considered statistically significant.

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Results 600 canals among 300 patients were investigated for the positional and anatomical variations of PC’s. Canals located under the floor were identified in 38.3% (230/600) (Figs. 2, 6); within-the-floor canals were encountered in 39.6% (238/600) (Figs. 3, 4, 5); and canals protruding into the sinus cavity (i.e., within sinus cavity) were observed in 22% (132/600). (Figs. 5, 6, 7, 8, 9). Dehiscence of the bony wall of PC was recognized in 26% (157/600) of canals (Figs. 4, 7, 9). Coexistence of PR and protruding PC was found in 16.5% (99/600) of canals, 7.3% (44/600) on the right side and 9.2% (55) on the left side. Statistically, there was significant association between PR and PC protrusion (p = 0.000) (Figs. 6, 8, 9).

Discussion

Fig. 3 Coronal CT image shows pterygoid canals within sinus floor (arrows)

Direct coronal CT scanning at 5-mm sections are often adequate for the evaluation of most sinonasal and skull base structures; however, 3-mm sections afford the best preoperative evaluation for endoscopic sinus survey [21]. As per our sinonasal protocol, we have used 4-mm contiguous slice thickness from anterior frontal sinus to anterior sphenoid sinus; and a 2-mm slice thickness was used exclusively in the sphenoid sinus region to enable better

Fig. 4 Coronal CT image shows pterygoid canals located within the sinus floor (arrows). Both canals show degree of loss of bony continuity (dehiscence)

Fig. 2 Coronal CT image shows pterygoid canals located under the sphenoid sinus floor (arrows)

evaluation of PC and its relation to sinus floor. Avoiding 1-mm sections would provide patients exposing to less radiation. In CT imaging, PC normally starts at the level of foramina ovale and terminates at pterygopalatine fossae (Fig. 10). Palatovaginal canal (between the sphenoid process of the palatine bone and the vaginal process of the vomer bone) passes in the floor of sphenoid sinus between the PC and vomerine crest (Fig. 11). The easiest way to detect pterygoid and palatovaginal canals, is to identify the inverted pear-shaped pterygopalatine fossa and follow its course posteriorly (Fig. 12). In this direction, it continues into two ovoid or round medial and lateral canals

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Fig. 7 Coronal CT image shows pterygoid canals protruded into sinus cavity (arrows). Right canal shows degree of dehiscence. Left canal connected to the floor with a stalk Fig. 5 Coronal CT image shows right pterygoid canal located within the sinus floor and separated into two parts by a septum (arrows). Left canal lies within sinus cavity and connected to the floor with a stalk

Fig. 6 Coronal CT scan image shows intrasinusal right pterygoid canal associated with pterygoid recess (asterisk). Left pterygoid canal located beneath the floor (arrow)

representing palatovaginal and PC’s, respectively, [17]. Foramen rotundum (round foramen) is rather located in the lateral wall of sphenoid sinus in the vicinity of greater wing of sphenoid bone (floor of middle cranial fossa) (Fig. 12). Relationship of PC with sphenoid sinus floor has been investigated in the literature. Lang and Keller [12] reported PC under the sphenoid sinus floor in 38% of cases, along the floor in 34%, and within the cavity in 18%. Pandolfo et al. [15] emphasized that there is a variable relationship

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Fig. 8 Coronal CT image shows bilateral protrusion of pterygoid canals (arrows) associated with bilateral pterygoid recesses (asterisks)

between PC and sphenoid sinus. They concluded that constriction of intrasinusal PC caused by concentric sclerosis of its wall, was generally due to chronic sinusitis. Without explaining their criteria, Fatih et al. [6] reported 36% of their 150 cases embedded in the sphenoid body (under the floor), and 64% protruded into the sinus cavity. We assume that they regarded PC’s along the sinus floor under the category of protrusion; this might explain the high frequency of protrusion. Fernandes [7] recognized that

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Fig. 11 Coronal CT image shows pterygoid canals (straight-end white arrows) and palatovaginal canals (bifid-end white arrows)

Fig. 9 Coronal CT image shows bilateral dehiscence of pterygoid canals (arrows). Left canals is protruded into the cavity and associated with pterygoid recess (asterisk)

Fig. 12 CT image shows inverted-pear shaped pterygopalatine fossae (asterisks) and foramina rotundum (white arrows) related to lateral sinus wall

Fig. 10 Coronal CT image shows foramina ovale (white arrows) and beginning of pterygoid canals (black arrows)

PC may run in the floor of the sphenoid sinus at varying depths depending on the degree of sphenoid sinus pneumatization. The most common detected positional variation in our series was the location of the canal along the floor of the sphenoid sinus. We were generous in our recognition criterion of canal dehiscence, as we were primarily concerned about the vulnerability of the canal rather than the literal existence of dehiscence; however, this position was reported in more than 39% of canals. Fathi et al. [6] reported dehiscence of the bony structure of the canal in 32%. Our study showed high variation of PC relative to the sphenoid sinus floor and cavity in terms of position and

dehiscence, this observation shows the necessity of careful CT road mapping prior to surgery in sphenoid sinus region. This report showed significant association between protruding PC and existence of PR. Kazkayasi et al. [11] reported the same conclusion in their study. Based on this observation, bearing in mind that sphenoid sinus disease can obscure the fine anatomical details on CT imaging, PR should be an indicator of PC protrusion unless otherwise depicted. Overall, there are no substantial differences between our results and those previously published. The ease in nerve identification is the key element in success of vidian neurectomy; in other words, the relationship of PC to the sinus floor dictates the surgical approach of Vidian neurectomy. PC’s located below the floor are best negotiated via transnasal approach; on the other hand, the transsphenoidal approach is considered for patients with PC’s located in the sinus floor or cavity [13].

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Conclusion To our knowledge, the present report appears to be the largest radio-anatomic study involved investigation of 600 PC’s of 300 peoples. This study serves as an appendix to radiological authorities in the description of anatomic relationship of PC to the floor and cavity of sphenoid sinus. Surgeons addressing vidian neurectomy must be familiar with the positional variations of PC in the preoperative CT images for easier and safer nerve identification and transection. Acknowledgments The authors would like to thank Ms. Fatma El-Sughaer, CT technologist, for skillful technical assistance, and Dr. Yousef El-Gomatti for help with statistical analysis. Conflict of interest of interest.

The authors declare that they have no conflict

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