/STRU^NI RAD UDK 616.321-007.67-089 DOI:10.2298/ACI0901017S Current concepts in the anatomy and origin of pharyngeal......................................... diverticula OM Skrobi}, AP. Simi}, NS Radovanovi}, BV [pica, PM Pe{ko Department of Esophagogastric Surgery, The First Surgical University Clinic, Clinical Center of Serbia, Belgrade, Serbia The role of this paper is to present the current ANATOMICAL AND TOPOGRAPHICAL concepts in anatomy and etiopathogenesis of pha- CONSIDERATIONS ryngeal diverticula. Precise anatomical considera- tions highly emphasizing the weak anatomic areas The UES is defined as an area of high intraluminal pres- which predispose the pouch formation are dis- sure that forms a barrier between the pharynx and the cer- cussed. Focus exposed in details will also be given vical esophagus. This definition implies three responses: tone generation, phasic response activity, and sphincter rezime upon the structural and functional characteristics of the upper esophageal sphincter as well as to its opening. The UES relaxes and opens during swallowing, physiological states, architecture and dynamic func- allowing the passage of food and liquids into the esopha- tions. A brief review of hystorical and current perspec- gus, while at the same time provides a barrier against its tives regarding the origin of pharyngeal diverticula retrograde flow. By doing so, he represents an important has also been given. Special attention is given to the protective function preventing aspiration of acidic gastric abnormal cricopharyngeal function in patients with content into the respiratory tract on one side, and on the pharyngeal pouches in the terms of altered UES com- other entry of air into the esophagus. The UES also per- pliance, importance of gastroesophageal reflux and mits, by its physiologic relaxation, retrograde flow of ma- histopathologic changes of cricopharyngeal muscle. terial during belching, and vomiting. Anatomically observed, the pharyngoesophageal junc- Key words: Upper esophageal sphincter, Zenker tion or area encompassing the tone generation function of diverticula, etiopathogenesis the UES is sometimes referred to as the pharyngoeso- INTRODUCTION phageal segment or sphincter (PES) as well as upper esophageal high-pressure zone (UEHPZ). Although the he upper esophageal sphincter (UES) serves a range physiologic concepts of UES are mostly clear, the Tof important physiologic functions. Unlike its coun- anatomic components of these concepts are not. By the terpart in the distal esophagus, we are only beginning structural anatomy standpoint, the pharyngoesophageal to unravel the normal workings of this sphincter and junction or UES represents a musculocartilaginous struc- how its function is disturbed by disease. A clear under- ture composed of the posterior surface of the thyroid and standing on the exact etiopathogenesis of pharyngeal cricoid cartilage, the hyoid bone, and three muscles: infe- pouches, strangely enough, is still lacking. rior pharyngeal constrictor (IPC), cricopharyngeus (CP) Several theories exist concerning the formation of these and cranial or cervical esophagus (CE).1,2,3,4 (Figure 1). CP pulsion diverticula and mostly are centered upon the together with the cranial part of the cervical esophagus structural or physiological abnormality of the UES, espe- constitutes the lower third of the entire pharyngoeso- cially on its most prominent part the cricopharyngeal phageal high-pressure zone, while the IPC muscle ac- muscle (CP). counts for the remaining upper two thirds of the UES.4 In this paper we will highlight current knowledge and The physiologic function of the UES is mainly based on review the literature concerning anatomy and physiology the sole activity of cricopharyngeal muscle. The CP is a of the pharyngoesophageal junction, with a special em- striated muscle attached to the cricoid cartilage that is in phasis on the cricopharyngeal muscle pathophysiology in average 1.9 cm in length in males and 1.6 cm in fe- the spectrum of pharyngeal pouches. males.1,3 CP forms a c-shaped muscular band that pro- duces maximum tension in anteroposterior rather than lat- 18 OM Skrobi} et al. ACI Vol. LVI eral directions. The CP is suspended between the cricoid processes, surrounds the narrowest part of pharynx, and extends caudally where it blends with the circular muscle of the cervical esophagus. Two sets of CP muscle fibers have been identified: the horizontally oriented fibers (pars fundiformis), which occlude the esophageal introitus, and an oblique band of fibers (pars obliqua), which are re- sponsible for propulsion of the bolus. Both types of fibers of CP extend from the lateral aspect of the cricoid carti- lage to the posterior midline raphe, where they blend su- periorly with the IPC.5 The horizontal fibers of the CP en- circle the upper esophagus, forming a sling between the two sides of the cricoid cartilage.6 The inferior pharyngeal constrictor muscle extends from the oblique line of the thyroid cartilage to insert into the posterior midline pharyngeal raphe, a fibrous band ex- tending from the base of the skull, to which all of the bands of constrictor muscles are attached. Unlike the IPC, the pars fundiformis of the CP has no median raphe.3,4 Killian’s triangle, also known as dehiscence, through which pharyngoesophageal Zenker diverticula occur, rep- resents an anatomical triangular area of sparse muscula- ture of the IPC, bordered superiorly by the firm oblique fi- bers of the IPC and inferiorly by the horizontal fibers of the CP, mostly lying in the posterior midline just above the cricopharyngeal sling and below the pharyngeal ra- phe.7,8,9,10 The cervical esophagus begins at the lower border of the FIGURE 1. cricoid cartilage and contains predominantly striated mus- ANATOMY OF THE PHARYNGOESOPHAGEAL JUNC- cle fibers, but occasionally smooth fibers are found in the TION. center of the muscle. The muscle fibers are arranged in two layers: the external layer containing longitudinal, and the internal layer containing circular or transversely ar- ranged fibers. The inner circular layer blends superiorly with the cricopharyngeus. The longitudinal layer, how- ever, diverges at its upper end approximately one to two cm from the CP, forming two bands that swing laterally and anteriorly around the esophagus to attach to a com- mon tendon behind the cricoid cartilage. Therefore, the posterior esophageal wall between these two diverging bands is the single circular layer of muscu- lar fibers. This forms the second potentially weak area, known as Laimer’s triangle or the Laimer-Haeckerman area.11 The external longitudinal layer courses down the length of the entire esophagus. At its distal end the longi- tudinal fibers become more oblique and end along the an- terior and posterior gastric wall.12 The internal circular FIGURE 2. layer of the esophageal muscle originates at the level of TYPES OF PHARYNGEAL DIVERTICULA AND THEIR cricoid cartilage and in descending forms incomplete cir- LOCATION. A) ZENKER DIVERTICULA, B) LAIMER DI- cles down to the esophagogastric junction. VERTICULA, C) KILLIAN-JAMEISON DIVERTICULA Another space of weakness at the pharyngoesophageal AND D) LATERAL PHARYNGEAL DIVERTICULA. junction is the Killian-Jamieson area. This is a muscular gap in the posterolateral wall located between the oblique pharyngeal fibers and inferiorly by the upper circular fi- and transverse fibers of the cricopharyngeal muscle. Some bers of the esophagus through which course the inferior authors describe this area as the space of the cervical laryngeal nerve, the inferior laryngeal artery, and laryn- esophagus inferior to the cricopharyngeus and lateral to geal lymphatics. the longitudinal muscle of the esophagus just below its in- In this area a Killian-Jamieson diverticulum can be sertion on the posterior lamina of the cricoid cartilage. formed13. It is important to differentiate this type of diver- This area is bounded superiorly by the lowest crico- ticulum from Zenkers, since the treatment approach is Br. 1 Current concepts in the anatomy and origins of 19 pharyngeal diverticula tion, and conventional wisdom holds that the CP is the major muscle of the UES. Several studies have investi- gated the separate role of CP, IPC and the cervical esophagus in the unique functioning of the UES.14,15 In rest, both IPC and CP muscle contribute equally, express- ing the similar neuromuscular activity which fluctuates in association with changes in the intraluminal pressure.16,17 Some of the intrinsic pressure of the UES is possibly contributed by the infracricoid esophagus, but continuous activity has not been recorded.15,16,17 UES contraction and relaxation during retching and vomiting occur by the si- multaneous action of the CP, IPC, and proximal cervical esophagus.16,18 During swallowing and belching, CP shows the most prominent drop in pressure and active re- laxation15,18, while on the other hand CP and IPC both show active contractility during coughing and sneezing19. UES contraction in response to esophageal or pharyngeal distension occurs mainly with the action of CP.15 Taking all this facts in account, of all UES muscles only the cricopharyngeal functions is present in all physiologi- FIGURE 3. cal states. CP is composed of striated muscle of small av- INERVATION OF THE PHARYNGOESOPHAGEAL JUNC- erage diameter fibers (25-35 m) which are not oriented in 20,21,22 TION a parallel fashion. These fibers are of predominantly slow twitch (type I), an oxidative skeletal muscle type im- portant