**1. Introduction**

As part of secondary lymphoid organs, mucosa-associated lymphoid tissue (MALT) is an aggregate of unencapsulated lymphoid tissue that is located diffusely in the mucosa of the aerodigestive tract and consists of the tonsils, vermiform appendix, and Peyer's patch [1]. As part of MALT, the tonsils serve as a protection ring including nasopharynx-associated lymphoid tissue (NALT), which is known as Waldeyer's tonsillar ring, around the entrance of the upper aerodigestive tract to start the initial immunological barrier to infections [1, 2]. This annular-shaped lymphoid ring contains four types of tonsils in a fixed position [3].


Due to the close proximity of the palatine tonsil with the surrounding spaces including parapharyngeal, retropharyngeal, masticator, and parotid spaces, the tumors and inflammation of the tonsil commonly spread into these spaces and result in secondary lesions [4, 5]. A detailed knowledge of the surgical anatomic landmarks in the tonsillar region and the spaces around it is required for preoperative planning and to prevent iatrogenic complications.

#### **2. Immune function of the tonsils in Waldeyer's ring**

The tonsils are lymphoepithelial organs acting as a guardian at the entrance of the upper aerodigestive tract. Lymphoid system, as a component of the immune system, consists of lymph vessels, nodes, and organs that regulate the immune response directly or indirectly. The lymph vessels play a key role in the drainage of interstitial fluid from the tissues to the blood and fat absorption, whereas the lymphoid organs mediate the proliferation and maturation of the cells of the immune system, which protect the body against ingested or inhaled foreign pathogens. The cell groups of the immune system, which is known as the ability to distinguish self from nonself, produce two reactions that are called the innate (natural) and adaptive (acquired) immunity [1, 2]. Initially, lymphocytes and accessory cells are developed and matured to the stage of antigen recognition in primary lymphoid organs including the thymus and bone marrow, and then they are activated and differentiated to effector cells of the immune response by antigen presentation in secondary lymphoid organs. The lymph nodes, the spleen, and mucosa-associated lymphoid tissue are secondary lymphoid organs which allow lymphocytes to become functional to produce a defense mechanism against microorganisms such as viruses, parasites, and bacteria. The structures of MALT have 70% of all the cells of the immune system, and the percentages of the lymphocytes in each of them are variable [1].

#### **3. Anatomical localization of the tonsils in the pharynx**

As part of the upper aerodigestive tract, the pharynx is located between the skull base and the inferior border of cricoid cartilage and consists of three portions; the nasopharynx (upper nasal), oropharynx (middle oral), and laryngopharynx (lower laryngeal). It is a musculomembranous tube covered with three external (circular, the superior, middle, and inferior constrictors) and three internal (longitudinal, voluntary) muscles, which play a key role in swallowing, respiration, and phonation [6]. The tonsils are located posterior to the nasal and oral portions of the pharynx to form a circumferential ring, known as the Waldeyer's tonsillar ring, which was first described by German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz [3]. The unpaired nasopharyngeal and lingual tonsils and the paired palatine and tubal tonsils form Waldeyer's lymphoid ring at the opening of the upper aerodigestive tract and are responsible for both innate and adaptive immunological responses which have a crucial role in the defense mechanism of the pharynx (**Figure 1**) [7].

#### **3.1 Nasopharynx**

As a part of the upper respiratory system, the nasopharynx is bounded by the choanae anteriorly, the upper surface of the soft palate inferiorly, and the

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the SPCm [7, 8].

**Figure 1.**

**3.2 Pharyngeal tonsil**

*Surgical Anatomy of the Tonsils*

*DOI: http://dx.doi.org/10.5772/intechopen.93038*

*The localization of the tonsils in Waldeyer's tonsillar ring.*

oropharyngeal isthmus (OPI) posterolaterally. The nasopharyngeal and tubal tonsils are located in the posterolateral wall of the nasopharynx [6]. The palatoglossal arch (PGa) and palatopharyngeal arch (PPa) join with each other to form the OPI which allows the communication with the oropharynx. The boundaries of the OPI are formed by the soft palate (velum) anteriorly and the lateral and posterior pharyngeal walls posterolaterally. During swallowing and speaking, the levator veli palatini (LVPm), palatopharyngeus (PPm), superior pharyngeal constrictor (SPCm), salpingopharyngeus (SPm), and the uvula, which are called a velopharyngeal sphincter, play a role in the closure of the OPI. During velopharyngeal function, a transverse mucosal ridge called Passavant's ridge (palatopharyngeal sphincter) runs along the posterior wall of the OPI between the most lateral part (transverse fibers) of the PPm and the most superior part of

Pharyngeal tonsil is the superior-most of the Waldeyer's ring and located above the soft palate in the posterosuperior roof of the nasopharynx as a single median unencapsulated mass with 12–15 shallow, crypt-like invaginations. The pharyngeal bursa, a blind mucosal sac, may be seen in the posterior median wall of the nasopharynx above the SPCm. A median longitudinal groove extends from this sac inferiorly [6]. Anterosuperiorly, the pharyngeal tonsil is usually lined by pseudostratified ciliated columnar epithelium (respiratory epithelium), whereas posteroinferiorly the areas adjacent to the oropharynx is covered by stratified epithelium. These mucosal folds containing numerous lymphoid

*Oral and Maxillofacial Surgery*

Due to the close proximity of the palatine tonsil with the surrounding spaces including parapharyngeal, retropharyngeal, masticator, and parotid spaces, the tumors and inflammation of the tonsil commonly spread into these spaces and result in secondary lesions [4, 5]. A detailed knowledge of the surgical anatomic landmarks in the tonsillar region and the spaces around it is required for preopera-

The tonsils are lymphoepithelial organs acting as a guardian at the entrance of the upper aerodigestive tract. Lymphoid system, as a component of the immune system, consists of lymph vessels, nodes, and organs that regulate the immune response directly or indirectly. The lymph vessels play a key role in the drainage of interstitial fluid from the tissues to the blood and fat absorption, whereas the lymphoid organs mediate the proliferation and maturation of the cells of the immune system, which protect the body against ingested or inhaled foreign pathogens. The cell groups of the immune system, which is known as the ability to distinguish self from nonself, produce two reactions that are called the innate (natural) and adaptive (acquired) immunity [1, 2]. Initially, lymphocytes and accessory cells are developed and matured to the stage of antigen recognition in primary lymphoid organs including the thymus and bone marrow, and then they are activated and differentiated to effector cells of the immune response by antigen presentation in secondary lymphoid organs. The lymph nodes, the spleen, and mucosa-associated lymphoid tissue are secondary lymphoid organs which allow lymphocytes to become functional to produce a defense mechanism against microorganisms such as viruses, parasites, and bacteria. The structures of MALT have 70% of all the cells of the immune system, and the percentages of the lymphocytes in each of them are

tive planning and to prevent iatrogenic complications.

**2. Immune function of the tonsils in Waldeyer's ring**

**3. Anatomical localization of the tonsils in the pharynx**

defense mechanism of the pharynx (**Figure 1**) [7].

As part of the upper aerodigestive tract, the pharynx is located between the skull base and the inferior border of cricoid cartilage and consists of three portions; the nasopharynx (upper nasal), oropharynx (middle oral), and laryngopharynx (lower laryngeal). It is a musculomembranous tube covered with three external (circular, the superior, middle, and inferior constrictors) and three internal (longitudinal, voluntary) muscles, which play a key role in swallowing, respiration, and phonation [6]. The tonsils are located posterior to the nasal and oral portions of the pharynx to form a circumferential ring, known as the Waldeyer's tonsillar ring, which was first described by German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz [3]. The unpaired nasopharyngeal and lingual tonsils and the paired palatine and tubal tonsils form Waldeyer's lymphoid ring at the opening of the upper aerodigestive tract and are responsible for both innate and adaptive immunological responses which have a crucial role in the

As a part of the upper respiratory system, the nasopharynx is bounded by the choanae anteriorly, the upper surface of the soft palate inferiorly, and the

**28**

**3.1 Nasopharynx**

variable [1].

**Figure 1.** *The localization of the tonsils in Waldeyer's tonsillar ring.*

oropharyngeal isthmus (OPI) posterolaterally. The nasopharyngeal and tubal tonsils are located in the posterolateral wall of the nasopharynx [6]. The palatoglossal arch (PGa) and palatopharyngeal arch (PPa) join with each other to form the OPI which allows the communication with the oropharynx. The boundaries of the OPI are formed by the soft palate (velum) anteriorly and the lateral and posterior pharyngeal walls posterolaterally. During swallowing and speaking, the levator veli palatini (LVPm), palatopharyngeus (PPm), superior pharyngeal constrictor (SPCm), salpingopharyngeus (SPm), and the uvula, which are called a velopharyngeal sphincter, play a role in the closure of the OPI. During velopharyngeal function, a transverse mucosal ridge called Passavant's ridge (palatopharyngeal sphincter) runs along the posterior wall of the OPI between the most lateral part (transverse fibers) of the PPm and the most superior part of the SPCm [7, 8].
