Clinical Anatomy 28:455–459 (2015)
ORIGINAL COMMUNICATION
Surface Anatomy of the Parotid Duct and its Clinical Relevance GAOUSSOU TOURE,1,2* JEAN-PHILIPPE FOY,1
AND
CHRISTIAN VACHER3
1
e de la Source, CHI L & R Aubrac, 94195 Service de Chirurgie Maxillo-Faciale, 40 Alle Villeneuve-Saint-Georges Cedex, France 2 Paris 5, Paris, France URDIA, EA 4465, Universite 3 ^ pital Beaujon, 100 bd du Ge ne ral Leclerc, 92110 Universite Paris 7, Service de Chirurgie Maxillofaciale, Ho Clichy, France
The trajectory of the parotid duct (PD) makes it vulnerable to injuries during facial trauma and facial rejuvenation procedures. The PD is usually represented as a straight line, although its description in the literature varies. Our objective was to study the trajectory of the PD and to define reliable cutaneous landmarks. We dissected 35 human cadaver half-heads. We defined three points: point I where the PD crossed a line (line 2) between point T (the intertragal incisura) and point C (the corner of the mouth), point S for the top of the PD, and point B where the PD penetrated the buccinator muscle. We measured the distance (D) between points T and C, the distance (d1) between points T and I, and the distance (d2) between points T and B. We also determined the height (h) of the orthogonal line between point S and line 2. We noted that for all of the half-heads that we examined, the PD followed a curved trajectory between points I and B above line 2. Point I was located 1/3 of the way along distance D. Point B was tangential to line 2, and was located 2/3 of the way along distance D. The average height measurement (h) was 1.4 cm. We demonstrated that the PD follows a curved trajectory from the 1/3 mark to the 2/3 mark along distance D, the top of this curve being 1.5 cm above the line TC. Clin. Anat. 28:455–459, 2015. VC 2015 Wiley Periodicals, Inc. Key words: parotid duct; landmark; buccinator muscle; surface anatomy
INTRODUCTION The parotid duct (PD) has frequently been described in anatomical studies owing to its close proximity to the transverse facial artery (Yang et al., 2010), the facial nerve (Pogrel et al., 1996; Erbil et al., 2007) and facial muscles. This is particularly the case for the buccinator muscle, which acts as a valve to prevent inflation of the duct during blowing (Amano et al., 2010). The trajectory of the PD has not been examined carefully, despite its exposure during maxillofacial, plastic, and ENT surgery. Indeed, the trajectory of the PD, which runs across the proximal surface of the cheek anterior to the masseter muscle, then through the buccal fat pad before perforating the buccinator muscle so as to enter the mouth, often exposes it to injury during clinical procedures. It can also be injured as a result of facial trauma, particularly in the case of
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wounds to the parotidomasseteric or buccal areas, which can lead to complications such as sialocele, salivary pseudo-cyst, or salivary fistula (Barton et al., 1976; Lewis and Knottenbelt, 1999; Steinberg and ra, 2005; Sujeeth and Dindawar, 2011). Cases Herre of sialocele resulting from facial rejuvenation
Abbreviations used: PD, parotid duct , Service de chirurgie *Correspondence to: Dr. Gaoussou Toure e de la Source, CHI L & R Aubrac, 94195 maxillo-faciale, 40 Alle Villeneuve-Saint-Georges Cedex, France. E-mail: gaoussou. [email protected] Received 18 June 2014; Revised 15 December 2014; Accepted 17 December 2014 Published online 12 February 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ca.22510
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Fig. 1. Side view of the parotid duct and parotid link to the buccinator muscle. T 5 tragus, pd 5 parotid duct, M 5 masseter muscle. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
procedures have also been reported, while PD laceration or compression have been observed with rhytidectomies (Nahlieli et al., 2008) and with Aptos thread techniques (Winkler et al., 2006). Injuries to the PD are also quite frequent during cutaneous tumor surgery, especially during Mohs procedures (Krishnan et al., 2009). Finally, complications have been observed with botulinum toxin injections (Kim et al., 2007; Hu et al., 2010). The trajectory of the PD is usually represented as a straight line, but there is a lack of consensus regarding its precise trajectory, and this rectilinear representation has not been substantiated by anatomical studies. Several straight lines have been used to evaluate the risk of PD lesions in cheek injuries. One of these lines runs from the tragus to the labial commissure, while another runs from the tragus to the nostril. It is unclear which, if any, of these lines truly represents the PD’s trajectory. Several papers have indicated the need to define accurate landmarks to improve knowledge of the location of the PD, as this could help avoid complications arising from PD injuries (Nahlieli et al., 2008; Krishnan et al., 2009). Our objective was to study the trajectory of the PD by examining its relationship to adjacent anatomical structures, and to define clinical landmarks for use in surgical procedures.
We methodically applied the same procedures to all of the subjects. The half-heads were free of scars, tumors and infectious diseases. Twenty of them were female and fifteen were male. Seventeen were left sides and eighteen were right sides. None of the 35 subjects exhibited overt signs of being overweight, and their mean age was 78 years. All of the subjects were white, though we have no indication that ethnicity influences the position of the PD. An initial superficial dissection was performed to identify the PD without puncturing the masseteric aponeurosis, so as to avoid modifying the PD anatomy by a deeper dissection (Fig. 1). Once the PD was correctly located, and after a complete dissection, we used the following three reference points: point T for the intertragal incisura, point N for the base of the nostril, and point C for the corner of the mouth. Two reference lines were drawn: line 1 between points T and N and line 2 between points T and C. We chose these points and lines because most of the PD representations suggested to date have fallen within in this region. We also defined three new reference points: point I where the PD crosses line 2, point S for the top of the PD, and point B where the PD penetrates the buccinator muscle. We divided the trajectory of the PD into three segments: the first segment lies between the parotid gland and the masseter, the second lateral to the masseter, and the third lateral to the buccinator. We measured the distance (D) between points T and C, the distance (d1) between points T and I, and the distance (d2) between points T and B. We determined the height (h) of the orthogonal line between point S and line 2 (Figs. 2 and 3). Finally, we calculated the ratios d1/D and d2/D.
RESULTS We noted that in all cases the PD followed a curved trajectory between points I and B above line 2, which was the most pertinent reference line. Point B was tangential to line 2.
MATERIALS AND METHODS We dissected 35 fresh human cadaver half-heads from 35 different subjects. The principles outlined in the Declaration of Helsinki were followed. The Paris Body Donation Center operates according to the laws enforced in France. Therefore, there is no need for approval by an ethics committee for research in an anatomy lab; respect for the donors’ bodies is obligatory.
Fig. 2. Table of the lines and reference points used. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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2008; Standring, 2008; Carlson and Ord, 2009; Vidimos, 2009; Andersson et al., 2010; Granick and Jacob, 2010; Hu et al., 2010; Manson, 2010; Bradley and Guntinas-Lichius, 2011; Demetriades and Newton, 2011; Guyot et al., 2011; Legome and Shockley, zy and 2011; Sinnatamby, 2011; Britt et al., 2012; Le Princ, 2012; Peitzman et al., 2012), three reference lines are commonly used to describe the trajectory of the PD (Fig. 5). These three are: a line between the tragus and the middle of the upper lip, a line between the tragus and the base of the nostril, and a line between the tragus and the labial commissure. In other cases, we observed several straight-line representations that were located between the first and the third lines, as shown in Figure 5. In our study, the most pertinent line was found to lie between point T and point C (line 2) which is equivalent to line C in Figure 5. The PD followed a trajectory that arches across this line, since the PD is formed by the fusion of the mandibular and maxillary prominences along a line between the tragus and the cheilion (Larsen, 2003). The PD followed a curve that crossed, or that was tangential to, reference line 2 at two points: near the origin of the PD at 1/3 of the length of segment TC, and at the point of penetration into the buccinator 2/3 of the way along that segment. Fig. 3. Superposition of a diagrammatic representation on an anatomical model. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
We further observed that the PD followed an ascending trajectory in its first segment, up to point S, which is located on the second segment, and then a descending trajectory lateral to the buccinator in the third segment. Our measurements are shown in Figure 4. The average d1/D ratio was 0.34 (i.e., about 1/3), which means that the PD crossed reference line 2 at a point located 1/3 of the way along distance D. The ratio d2/D was 0.64 (i.e., about 2/3), and hence the PD penetrated the buccinator muscle on line 2 at a point located 2/3 along the distance D. The average value of h was 1.4 cm.
DISCUSSION Although the PD has generally been described as a straight line, we have established in this study that it is, in fact, curved. Indeed, we noted that in 36 reference books for anatomy and salivary gland pathology or original articles (Ginestet, 1967; Guerrier, 1988; Pons and Bellavoir, 1988; Rouvie `re and Delmas, 1991; Deboise, 1993; Revol and Servant, 1993; Banzet and Servant, 1994; Chevrel and Fontaine, 1996; Lewandowski, 2000; Seiden, 2002; Kendell and Foost, 2005; Park, 2005; Powers et al., 2005; Stein ra, 2005; Bailey et al., 2006; Dhem berg and Herre , 2006; Fischer et al., 2006; Stong et al., and Gouaze 2006; Water and Staecker, 2006; Patel, 2007; Singh,
Fig. 4.
Table of the measurements.
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Fig. 5. Summary of data in the published literature. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
A limited number of previous studies have examined the trajectory of the PD, and most of these have considered it in relation to other anatomical structures. For instance, the buccal branches of facial nerve have been classified in relation to the PD (Saylam et al., 2006; Vidimos, 2009). Richards et al., observed that the facial nerve performed a loop above, or lateral to, the PD (Richards et al., 2004). Yang and colleagues used the PD as a landmark to describe the transverse facial artery (Yang et al., 2010). In our analysis, we focused on the trajectory of the PD in relation to consistent cutaneous landmarks that are employed in the clinical setting. In the few studies that have specifically examined the trajectory of the PD, the majority represent it as following a straight line. By analyzing 40 adult Korean human cadaver halfheads, Hu and colleagues found that the PD was above the tragus-cheilion reference line in 42.1% of cases. It crossed the line from the posteroinferior to the anterosuperior direction in 36.8%, it was on the reference line in 18.4%, and it was below the reference line in 2.6% (Hu et al., 2010). Among the 14 cases in which the PD crossed the reference line, this intersection was on the anterior third of the masseter muscle in two cases, on the middle third in nine, and on the posterior third in three (Krishnan et al., 2009). In our study, we noted that the PD crossed the same reference line (line 2 in our designation), and then continued above it following a curved trajectory. The PD was under the other reference line that we used (line 1 in our designation). Parker et al., published anatomical observations during orthodromic temporalis tendon transfer (Parker et al., 2012). They studied 20 half-heads from 10 subjects, and they created a PD reference line by
connecting the central point of the upper lip to the tragus. The PD was found to lie under this line, but the number of subjects studied was limited. Stringer et al. (2012) mapped the surface anatomy of the PD in 50 healthy adults using ultrasound. They showed that the surface anatomy of the PD was more accurately represented by the middle half of a line between the lower border of the tragus and the cheilion, and that it ran within 1.5 cm of this line in more than 90% of cases (Stringer et al., 2012). Thus, our results indicate that contemporary representations of the PD are incorrect, and that our data describe this area more accurately. Like Stringer et al. (2012), we found only a few surface anatomy studies of the PD in the literature. Oppenheim and Wing studied the surface anatomy in live subjects using sialography (Oppenheim and Wing, 1960), while the reports by Hu et al. (2010) and Parker et al. (2012) were based on cadaver dissections. In these studies, the PD was described as following a straight line. Our observations are not in agreement with this description. We observed a curved trajectory for the PD. As in these other investigators, we observed that line 1, which joins the intertragal incisura (T) to the base of the nostril, is not a useful guideline. For clinical purposes, we propose the use of line 2. This line connects the intertragal incisura (T) to the corner of the mouth (C). The top of the PD curve was approximately 1.5 cm above the line between the tragus (intertragal incisura) and the corner of the mouth. Our study could have been improved by dissecting more samples, and by examining the effect of the accessory parotid gland on the trajectory of the PD. Also, while the PD is a fixed structure and there is no evidence of post-mortem changes in its trajectory, it is nonetheless theoretically possible that post-mortem changes do occur.
Surface Anatomy and Landmarks of Parotid Duct Thus, in conclusion, these anatomical landmarks and measurements improve our knowledge of the location of the PD, and they are easy to use in clinical applications.
ACKNOWLEDGMENTS The authors thank the cadaver donors, who made this research possible.
REFERENCES Amano K, Moriyama H, Shimada K, Matsumura G. 2010. Morphological study of the fetal parotid duct and buccinator muscle and the relationship to salivary secretion. Clin Anat 23:642–648. Andersson L, Kahnberg K-E, Pogrel MA. 2010. Oral and Maxillofacial Surgery. John Wiley & Sons. Banzet P, Servant JM. 1994. Chirurgie plastique, reconstructrice et tique. Flammarion. esthe Barton NW, Miller SH, Graham WP III. 1976. Managing lacerations of the parotid gland, duct and facial nerve. Am Fam Physician 13: 130–134. Bailey BJ, Johnson JT, Newlands SD. 2006. Head & neck surgery— otolaryngology. Lippincott Williams & Wilkins. Bradley P, Guntinas-Lichius O. 2011. Salivary gland disorders and diseases: Diagnosis and management. Thieme. Britt LD, Peitzman A, Barie P, Jurkovich G. 2012. Acute care surgery. Lippincott Williams & Wilkins. Carlson E, Ord R. 2009. Textbook and color atlas of salivary gland pathology: Diagnosis and management. John Wiley & Sons. ^ te et cou. Chevrel JP, Fontaine C. 1996. Anatomie clinique Tome 3 Te France: Springer Verlag. Deboise A. 1993. Techniques en chirurgie oro-maxillo-faciale. Ellipses. Demetriades D, Newton E. 2011. Color atlas of emergency trauma. Cambridge University Press. A. 2006. Sobotta Atlas D’anatomie Humaine. 14th Dhem A, Gouaze dicales Internationals. Ed. Vol. 1. Editions Me Erbil KM, Uz A, Hayran M, Mas N, Senan S, Tuncel M. 2007. The relationship of the parotid duct to the buccal and zygomatic branches of the facial nerve: An anatomical study with parameters of clinical interest. Folia Morphol (Warsz) 66:109–114. ratoire: Chirurgie plastique et Ginestet G. 1967. Atlas technique ope reconstructive de la face. Flammarion. Granick MS, Jacob LM. 2010. Head and neck embryology and anatomy. In: Weinzweig J, editor. Plastic Surgery Secrets Plus. 2nd Ed. Mosby Elsevier. p 3492350. de technique chirurgicale o.r.l. et cervicoGuerrier Y. 1988. Traite faciale. Masson Guyot L, Seguin P, Benateau H. 2011. Techniques en chirurgie maxillo-faciale et plastique de la face. Springer. Hu K-S, Kim S-T, Hur M-S, et al. 2010. Topography of the masseter muscle in relation to treatment with botulinum toxin type A. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 110:167–171. Kendell BD, Foost DE. 2005. Applied surgical anatomy of the head and neck: Parotid region. In: Fonseca R, et al., editors. Oral and Maxillofacial Trauma. Vol. 1, 3rd Ed. Saunders: St. Louis Elsevier. p 324. Kim J-H, Shin JH, Kim ST, Kim C-Y. 2007. Effects of two different units of botulinum toxin type a evaluated by computed tomography and electromyographic measurements of human masseter muscle. Plast Reconstr Surg 119:711–717. Krishnan RS, Clark DP, Donnelly HB. 2009. The use of botulinum toxin in the treatment of a parotid duct injury during Mohs surgery and review of management options. Dermatol Surg 35: 941–947. Larsen WJ. 2003. Embryologie humaine. De Boeck & Larcier. p 378. Legome E, Shockley LW. 2011. Trauma: A comprehensive emergency medicine approach. Cambridge University Press.
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Lewandowski J. 2000. Assessment of nonorthopedic sports injuries: A sideline reference manual. SLACK Incorporated. Lewis G, Knottenbelt JD. 1991. Parotid duct injury: Is immediate surgical repair necessary? Injury 22:407–409. zy J-P, Princ G. 2012. Pathologie maxillo-faciale et stomatologie. Le Elsevier Masson. Manson PN. 2010. Assessment and management of facial injuries. In: Weinzweig J, editor. Plastic Surgery Secrets Plus. 2nd Ed. Mosby Elsevier. p 277. Nahlieli O, Abramson A, Shacham R, Puterman MB, Baruchin AM. 2008. Endoscopic treatment of salivary gland injuries due to facial rejuvenation procedures. Laryngoscope 118:763–767. Oppenheim H, Wing M. 1960. Sialography and surface anatomy of the parotid duct. AMA Arch Otolaryngol 71:80–83. Park SP. 2005. Facial plastic surgery—The essential guide. Thieme. Parker NP, Eisler LS, Dresner HS, Walsh WE. 2012. Orthodromic temporalis tendon: Anatomical considerations. Arch Facial Plast Surg 14:39–44. Patel M. 2007. Surgical techniques for parotid and submandibular glands and branchial cysts. In: Booth PW, Schendel SA, Hausamen JE, editors. Maxillofacial surgery. Vol.1, 2nd Ed. St. Louis: Churchill Livingstone Elsevier. p 681. Peitzman AB, Schwab CW, Yealy DM, Rhodes M, Fabian TC. 2012. The trauma manual: Trauma and acute care surgery. Lippincott Williams & Wilkins. Pogrel MA, Schmidt B, Ammar A. 1996. The relationship of the buccal branch of the facial nerve to the parotid duct. J Oral Maxillofac Surg 54:71–73. Pons J, Bellavoir A. 1988. Traumatologie faciale. Expansion scientifique franc ¸aise. Powers MP, Beck BW, Holton JB. 2005. Management of soft tissue injuries: Injuries to structures requiring special treatment. In: Fonseca R, et al, editors. Oral and maxillofacial trauma. Vol. 2, 3rd Ed. St. Elsevier Saunders. p 803. Revol M, Servant J-M. 1993. Manuel de chirurgie plastique reconstructrice et esthetique. Pradel. Richards AT, Digges N, Norton NS, et al. 2004. Surgical anatomy of the parotid duct with emphasis on the major tributaries forming the duct and the relationship of the facial nerve to the duct. Clin Anat 17:463–467. dition. Rouvie `re H, Delmas A. 1991. Anatomie humaine 13e `me e Elsevier Masson. Saylam C, Ucerler H, Orhan M, Ozek C. 2006. Anatomic landmarks of the buccal branches of the facial nerve. Surg Radiol Anat 28: 462–467. Seiden AM. 2002. Otolaryngology: The essentials. Thieme. Singh I. 2008. Textbook of anatomy with colour atlas. Jaypee Brothers Publishers. Sinnatamby CS. 2011. Last’s anatomy: Regional and applied. Churchill Livingstone Elsevier. p 359. Standring S. 2008. Gray’s anatomy: The anatomical basis of clinical practice. Churchill Livingstone Elsevier. p 496–497. ra AF. 2005. Management of parotid duct injuries. Steinberg MJ, Herre Oral Surg Oral Med Oral Pathol Oral Radiol Endod 99:136–141. Stong BC, Johns ME, Johns MM III. 2006. Anatomy and physiology of the salivary glands. In: Bailey BJ, Johnson JT, Newlands SD, editors. Head & neck surgery–otolaryngology. 4th Ed. Philadelphia: Lippincott Williams & Wilkins. p 5172526. Stringer MD, Mirjalili SA, Meredith SJ, Muirhead JC. 2012. Redefining the surface anatomy of the parotid duct: An in vivo ultrasound study. Plast Reconstr Surg 130:1032–1037. Sujeeth S, Dindawar S. 2011. Parotid duct repair using an epidural catheter. Int J Oral Maxillofac Surg 40:747–748. Vidimos AT. 2009. Dermatologic Surgery. Elsevier Health Sciences. Water TRVD, Staecker H. 2006. Otolaryngology: Basic Science and Clinical Review. Thieme. Winkler E, Goldan O, Regev E, Mendes D, Orenstein A, Haik J. 2006. Stensen duct rupture (sialocele) and other complications of the Aptos thread technique. Plast Reconstr Surg 118:1468–1471. Yang H-J, Gil Y-C, Lee H-Y. 2010. Topographical anatomy of the transverse facial artery. Clin Anat 23:168–178.
ORIGINAL COMMUNICATION
Surface Anatomy of the Parotid Duct and its Clinical Relevance GAOUSSOU TOURE,1,2* JEAN-PHILIPPE FOY,1
AND
CHRISTIAN VACHER3
1
e de la Source, CHI L & R Aubrac, 94195 Service de Chirurgie Maxillo-Faciale, 40 Alle Villeneuve-Saint-Georges Cedex, France 2 Paris 5, Paris, France URDIA, EA 4465, Universite 3 ^ pital Beaujon, 100 bd du Ge ne ral Leclerc, 92110 Universite Paris 7, Service de Chirurgie Maxillofaciale, Ho Clichy, France
The trajectory of the parotid duct (PD) makes it vulnerable to injuries during facial trauma and facial rejuvenation procedures. The PD is usually represented as a straight line, although its description in the literature varies. Our objective was to study the trajectory of the PD and to define reliable cutaneous landmarks. We dissected 35 human cadaver half-heads. We defined three points: point I where the PD crossed a line (line 2) between point T (the intertragal incisura) and point C (the corner of the mouth), point S for the top of the PD, and point B where the PD penetrated the buccinator muscle. We measured the distance (D) between points T and C, the distance (d1) between points T and I, and the distance (d2) between points T and B. We also determined the height (h) of the orthogonal line between point S and line 2. We noted that for all of the half-heads that we examined, the PD followed a curved trajectory between points I and B above line 2. Point I was located 1/3 of the way along distance D. Point B was tangential to line 2, and was located 2/3 of the way along distance D. The average height measurement (h) was 1.4 cm. We demonstrated that the PD follows a curved trajectory from the 1/3 mark to the 2/3 mark along distance D, the top of this curve being 1.5 cm above the line TC. Clin. Anat. 28:455–459, 2015. VC 2015 Wiley Periodicals, Inc. Key words: parotid duct; landmark; buccinator muscle; surface anatomy
INTRODUCTION The parotid duct (PD) has frequently been described in anatomical studies owing to its close proximity to the transverse facial artery (Yang et al., 2010), the facial nerve (Pogrel et al., 1996; Erbil et al., 2007) and facial muscles. This is particularly the case for the buccinator muscle, which acts as a valve to prevent inflation of the duct during blowing (Amano et al., 2010). The trajectory of the PD has not been examined carefully, despite its exposure during maxillofacial, plastic, and ENT surgery. Indeed, the trajectory of the PD, which runs across the proximal surface of the cheek anterior to the masseter muscle, then through the buccal fat pad before perforating the buccinator muscle so as to enter the mouth, often exposes it to injury during clinical procedures. It can also be injured as a result of facial trauma, particularly in the case of
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wounds to the parotidomasseteric or buccal areas, which can lead to complications such as sialocele, salivary pseudo-cyst, or salivary fistula (Barton et al., 1976; Lewis and Knottenbelt, 1999; Steinberg and ra, 2005; Sujeeth and Dindawar, 2011). Cases Herre of sialocele resulting from facial rejuvenation
Abbreviations used: PD, parotid duct , Service de chirurgie *Correspondence to: Dr. Gaoussou Toure e de la Source, CHI L & R Aubrac, 94195 maxillo-faciale, 40 Alle Villeneuve-Saint-Georges Cedex, France. E-mail: gaoussou. [email protected] Received 18 June 2014; Revised 15 December 2014; Accepted 17 December 2014 Published online 12 February 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ca.22510
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Fig. 1. Side view of the parotid duct and parotid link to the buccinator muscle. T 5 tragus, pd 5 parotid duct, M 5 masseter muscle. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
procedures have also been reported, while PD laceration or compression have been observed with rhytidectomies (Nahlieli et al., 2008) and with Aptos thread techniques (Winkler et al., 2006). Injuries to the PD are also quite frequent during cutaneous tumor surgery, especially during Mohs procedures (Krishnan et al., 2009). Finally, complications have been observed with botulinum toxin injections (Kim et al., 2007; Hu et al., 2010). The trajectory of the PD is usually represented as a straight line, but there is a lack of consensus regarding its precise trajectory, and this rectilinear representation has not been substantiated by anatomical studies. Several straight lines have been used to evaluate the risk of PD lesions in cheek injuries. One of these lines runs from the tragus to the labial commissure, while another runs from the tragus to the nostril. It is unclear which, if any, of these lines truly represents the PD’s trajectory. Several papers have indicated the need to define accurate landmarks to improve knowledge of the location of the PD, as this could help avoid complications arising from PD injuries (Nahlieli et al., 2008; Krishnan et al., 2009). Our objective was to study the trajectory of the PD by examining its relationship to adjacent anatomical structures, and to define clinical landmarks for use in surgical procedures.
We methodically applied the same procedures to all of the subjects. The half-heads were free of scars, tumors and infectious diseases. Twenty of them were female and fifteen were male. Seventeen were left sides and eighteen were right sides. None of the 35 subjects exhibited overt signs of being overweight, and their mean age was 78 years. All of the subjects were white, though we have no indication that ethnicity influences the position of the PD. An initial superficial dissection was performed to identify the PD without puncturing the masseteric aponeurosis, so as to avoid modifying the PD anatomy by a deeper dissection (Fig. 1). Once the PD was correctly located, and after a complete dissection, we used the following three reference points: point T for the intertragal incisura, point N for the base of the nostril, and point C for the corner of the mouth. Two reference lines were drawn: line 1 between points T and N and line 2 between points T and C. We chose these points and lines because most of the PD representations suggested to date have fallen within in this region. We also defined three new reference points: point I where the PD crosses line 2, point S for the top of the PD, and point B where the PD penetrates the buccinator muscle. We divided the trajectory of the PD into three segments: the first segment lies between the parotid gland and the masseter, the second lateral to the masseter, and the third lateral to the buccinator. We measured the distance (D) between points T and C, the distance (d1) between points T and I, and the distance (d2) between points T and B. We determined the height (h) of the orthogonal line between point S and line 2 (Figs. 2 and 3). Finally, we calculated the ratios d1/D and d2/D.
RESULTS We noted that in all cases the PD followed a curved trajectory between points I and B above line 2, which was the most pertinent reference line. Point B was tangential to line 2.
MATERIALS AND METHODS We dissected 35 fresh human cadaver half-heads from 35 different subjects. The principles outlined in the Declaration of Helsinki were followed. The Paris Body Donation Center operates according to the laws enforced in France. Therefore, there is no need for approval by an ethics committee for research in an anatomy lab; respect for the donors’ bodies is obligatory.
Fig. 2. Table of the lines and reference points used. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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2008; Standring, 2008; Carlson and Ord, 2009; Vidimos, 2009; Andersson et al., 2010; Granick and Jacob, 2010; Hu et al., 2010; Manson, 2010; Bradley and Guntinas-Lichius, 2011; Demetriades and Newton, 2011; Guyot et al., 2011; Legome and Shockley, zy and 2011; Sinnatamby, 2011; Britt et al., 2012; Le Princ, 2012; Peitzman et al., 2012), three reference lines are commonly used to describe the trajectory of the PD (Fig. 5). These three are: a line between the tragus and the middle of the upper lip, a line between the tragus and the base of the nostril, and a line between the tragus and the labial commissure. In other cases, we observed several straight-line representations that were located between the first and the third lines, as shown in Figure 5. In our study, the most pertinent line was found to lie between point T and point C (line 2) which is equivalent to line C in Figure 5. The PD followed a trajectory that arches across this line, since the PD is formed by the fusion of the mandibular and maxillary prominences along a line between the tragus and the cheilion (Larsen, 2003). The PD followed a curve that crossed, or that was tangential to, reference line 2 at two points: near the origin of the PD at 1/3 of the length of segment TC, and at the point of penetration into the buccinator 2/3 of the way along that segment. Fig. 3. Superposition of a diagrammatic representation on an anatomical model. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
We further observed that the PD followed an ascending trajectory in its first segment, up to point S, which is located on the second segment, and then a descending trajectory lateral to the buccinator in the third segment. Our measurements are shown in Figure 4. The average d1/D ratio was 0.34 (i.e., about 1/3), which means that the PD crossed reference line 2 at a point located 1/3 of the way along distance D. The ratio d2/D was 0.64 (i.e., about 2/3), and hence the PD penetrated the buccinator muscle on line 2 at a point located 2/3 along the distance D. The average value of h was 1.4 cm.
DISCUSSION Although the PD has generally been described as a straight line, we have established in this study that it is, in fact, curved. Indeed, we noted that in 36 reference books for anatomy and salivary gland pathology or original articles (Ginestet, 1967; Guerrier, 1988; Pons and Bellavoir, 1988; Rouvie `re and Delmas, 1991; Deboise, 1993; Revol and Servant, 1993; Banzet and Servant, 1994; Chevrel and Fontaine, 1996; Lewandowski, 2000; Seiden, 2002; Kendell and Foost, 2005; Park, 2005; Powers et al., 2005; Stein ra, 2005; Bailey et al., 2006; Dhem berg and Herre , 2006; Fischer et al., 2006; Stong et al., and Gouaze 2006; Water and Staecker, 2006; Patel, 2007; Singh,
Fig. 4.
Table of the measurements.
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Toure et al.
Fig. 5. Summary of data in the published literature. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
A limited number of previous studies have examined the trajectory of the PD, and most of these have considered it in relation to other anatomical structures. For instance, the buccal branches of facial nerve have been classified in relation to the PD (Saylam et al., 2006; Vidimos, 2009). Richards et al., observed that the facial nerve performed a loop above, or lateral to, the PD (Richards et al., 2004). Yang and colleagues used the PD as a landmark to describe the transverse facial artery (Yang et al., 2010). In our analysis, we focused on the trajectory of the PD in relation to consistent cutaneous landmarks that are employed in the clinical setting. In the few studies that have specifically examined the trajectory of the PD, the majority represent it as following a straight line. By analyzing 40 adult Korean human cadaver halfheads, Hu and colleagues found that the PD was above the tragus-cheilion reference line in 42.1% of cases. It crossed the line from the posteroinferior to the anterosuperior direction in 36.8%, it was on the reference line in 18.4%, and it was below the reference line in 2.6% (Hu et al., 2010). Among the 14 cases in which the PD crossed the reference line, this intersection was on the anterior third of the masseter muscle in two cases, on the middle third in nine, and on the posterior third in three (Krishnan et al., 2009). In our study, we noted that the PD crossed the same reference line (line 2 in our designation), and then continued above it following a curved trajectory. The PD was under the other reference line that we used (line 1 in our designation). Parker et al., published anatomical observations during orthodromic temporalis tendon transfer (Parker et al., 2012). They studied 20 half-heads from 10 subjects, and they created a PD reference line by
connecting the central point of the upper lip to the tragus. The PD was found to lie under this line, but the number of subjects studied was limited. Stringer et al. (2012) mapped the surface anatomy of the PD in 50 healthy adults using ultrasound. They showed that the surface anatomy of the PD was more accurately represented by the middle half of a line between the lower border of the tragus and the cheilion, and that it ran within 1.5 cm of this line in more than 90% of cases (Stringer et al., 2012). Thus, our results indicate that contemporary representations of the PD are incorrect, and that our data describe this area more accurately. Like Stringer et al. (2012), we found only a few surface anatomy studies of the PD in the literature. Oppenheim and Wing studied the surface anatomy in live subjects using sialography (Oppenheim and Wing, 1960), while the reports by Hu et al. (2010) and Parker et al. (2012) were based on cadaver dissections. In these studies, the PD was described as following a straight line. Our observations are not in agreement with this description. We observed a curved trajectory for the PD. As in these other investigators, we observed that line 1, which joins the intertragal incisura (T) to the base of the nostril, is not a useful guideline. For clinical purposes, we propose the use of line 2. This line connects the intertragal incisura (T) to the corner of the mouth (C). The top of the PD curve was approximately 1.5 cm above the line between the tragus (intertragal incisura) and the corner of the mouth. Our study could have been improved by dissecting more samples, and by examining the effect of the accessory parotid gland on the trajectory of the PD. Also, while the PD is a fixed structure and there is no evidence of post-mortem changes in its trajectory, it is nonetheless theoretically possible that post-mortem changes do occur.
Surface Anatomy and Landmarks of Parotid Duct Thus, in conclusion, these anatomical landmarks and measurements improve our knowledge of the location of the PD, and they are easy to use in clinical applications.
ACKNOWLEDGMENTS The authors thank the cadaver donors, who made this research possible.
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