The laryngeal saccule is an important clinical structure that is only just briefly mentioned in two of the major medical anatomy textbooks (Drake et al.,2005; Moore and Dalley,2006) and presumably little mentioned in most anatomy lectures on the larynx. John Hilton gave the first detailed description of the laryngeal saccule in 1837 (Iversen,1977). It is a blind pouch that arises from the anterior roof of the laryngeal ventricle and ascends in the loose areolar tissue of the pre-epiglottic space posterior to the thyroid cartilage (Fig. 1). The connective tissue in this region is weaker than in other portions of the larynx and provides no significant barrier between the ventricle and surrounding structures (Putney,1968). The histological features of the saccule include pseudostratified columnar epithelium, similar to other portions of the respiratory tract, as well as mixed mucous and serous glands found in the submucosa (Iversen,1977). In children, the saccule often displays lymphocytic infiltration and formation of lymphoid follicles. Kracke et al. (1997) found the incidence of laryngeal lymphoid tissue to be around 80%. In adults, however, lymphoid tissue is typically seen only in conjunction with pathologic conditions such as carcinoma (Delahunty and Cherry,1969).
Among higher primates such as gibbons and siamangs, air sacs extend bilaterally from the ventricle to form large chambers that can be inflated in the anterior neck. In chimpanzees, the laryngeal airspace gives rise to a central diverticulum and two lateral extensions. The two lateral air sacs are often of unequal size and can extend inferiorly into the anterior chest wall and even into the axilla. The gorilla and orangutan have the most complicated system of air sacs arising from the saccule; these diverticula fan out into the neck, and over the mandible and anterior thoracic wall (Swindler and Wood,1973).
The exact function of the saccule still remains a mystery, but Hilton proposed that it lubricated the ipsilateral vocal cord during speech and deglutition. This theory was endorsed by Pressman in 1942 when he, based on motion picture studies, observed simultaneous mucous ejection from the saccule and adduction of the vocal cords (Delahunty and Cherry,1969). Portions of the thyroepiglottic and aryepiglottic muscles surround the saccule and can purportedly compress it; thus, these fibers form the so-called compressor sacculi laryngis, which Hilton described more than a century ago (Delahunty and Cherry,1969).
The lubricating function of the saccule may be the only purpose of the saccule in man, but classically in gibbons and siamangs the saccule is thought to increase the resonance of vocalization and allows for rapid phonation during complex call sequences. Several theories suggest that the saccule in primates increases vocalization resonance, provides mechanical support for the jaw, and that laryngeal diverticula function to re-breathe exhaled air and prevent hyperventilation during rapid vocalization (Delahunty and Cherry,1969; Swindler and Wood,1973; Hewitt et al.,2002; de Boer,2009).
The laryngeal saccule in anthropoid primates and humans can become infected, leading to contiguous spread into neighboring tissues and even the death of the individual. One postulated mechanism for chronic laryngitis in humans is recurrent infection of the saccule draining directly onto the vocal folds (Broyles,1959). Swinburne (1952) discussed yet another infective process of the larynx in humans whereby laryngeal tuberculosis (TB) or syphilis can cause prolapse of the ventricle and saccule into the airway causing obstruction. Laryngeal TB is now quite rare in developed nations due to early identification and treatment, but laryngeal TB was found in as many as 50% of patients with pulmonary TB at the turn of the 20th century (Travis et al.,1976).
A laryngocele is a relatively rare pathology that may account for 5% of benign laryngeal disease (Mitroi et al.,2011). Close et al. (1987) found the incidence of laryngocele to be 8.6% in normal larynges, based on a case series. This rate was similar to the incidence demonstrated by Broyles (1959) from pathologic sections.
Formation of a laryngocele involves abnormal dilation of the saccule and ventricle of the larynx. This process can be congenital or acquired. Burke and Golden (1958) defined a laryngocele as a saccule that extends beyond the superior border of the thyroid cartilage, but many physicians today recognize a symptomatic dilation of the saccule as a laryngocele even if the aforementioned criterion is not met (Mitroi et al.,2011). There is a male predominance of the disease, and it is often seen in horn players or glassblowers (Birt,1987; Lancella et al.,2007; Mitroi et al.,2011). Internal laryngoceles are submucosal in nature and confined within the laryngeal cartilages, whereas external laryngoceles penetrate the thyrohyoid membrane to extend into the lateral neck. Mixed laryngoceles have both internal and external portions (Celin et al.,1991).
Laryngoceles exert mass effect on surrounding structures that can present as a lateral, reducible swelling in the neck if external, or as a mass within the airway if internal. Signs and symptoms of an internal laryngocele include dyspnea, hoarseness, globus sensation, and in some serious cases airway obstruction. A patient with an external laryngocele would likely present with fewer respiratory issues. There is a well-documented association between laryngeal carcinoma and laryngocele. Therefore, whenever a laryngocele is found, cancer must be considered in the differential diagnosis (Lancella et al.,2007). Mitroi et al. (2011) proposed that a laryngeal tumor could create a ball-valve effect resulting in air trapping and overinflation of the saccule resulting in development of a laryngocele. It is also possible that laryngeal carcinoma increases pressure in the airway resulting in saccular dilation, but neither of these theories relating carcinoma to laryngocele has been proven (Celin et al.,1991). Because of inconsistency of physical exam findings of laryngoceles, the gold standard for diagnosis is a computed tomography scan (Lancella et al.,2007) (Fig. 2). Imaging can easily differentiate a laryngocele from other causes of a neck mass such as a thyroid nodule, ranula, branchial cleft cyst, or carcinoma. The definitive treatment is surgical resection, with an external approach through the thyrohyoid membrane allowing the surgeon to spare the vocal cords from injury (Putney,1968). An endoscopic approach with use of a CO2 laser to marsupialize the lesion is only favorable for small internal laryngoceles (Lancella et al.,2007).
While the saccule may seem clinically unimportant, there is significant pathology associated with it including laryngocele, infection, airway obstruction, and even carcinoma. We therefore suggest that it be discussed in more detail during undergraduate medical school anatomy presentations on the larynx and in associated textbooks.
The authors thank Dr. Stacey Halum for providing access to the CT image presented in this article. They also thank Ms. Roberta Shadle for drawing Figure 1.