http://orcid.org/0000-0001-7420-1233
Case reports or small series reports are often viewed as minor or not worthy of publication, maybe because they do not increase the impact factor of a journal [Citation1]. However, for many decades, if not centuries, report of cases was the only kind of literature in medicine [Citation1]. Nowadays, they are still very useful, because they open discussions that help understanding rarities, as is the case of the article by Cohn et al. [Citation2] on bronchogenic cysts.
The authors present six cases of bronchogenic cysts at diverse locations (midline neck and chest wall, thyroid, subcarinal, posterior mediastinum) [Citation2]. As well discussed in the article, these malformations present across specialties and require different surgical approaches. This apparently leads in diverse terminologies and lack of a thorough understanding of the migration mechanisms to these locations and correlation between them. Therefore, some more clear explanation of the embryogenesis is needed.
Cohn et al. [Citation2] provide the classical theory that bronchogenic cysts are generated as a result of abnormal bronchial budding of the small lung bud given from the ventral wall of the pharynx. Others have proposed an origin from an accessory lung bud [Citation3] or from an accessory bronchus [Citation4]. Besides, it should be understood that the primitive trachea and esophagus are packed in a mass of mesenchyme, which will be the future mediastinum. The mediastinum tissue is continuous with the root of the neck cephalad, and the septum transversum just below; the latter will form the tendinous center of the diaphragm. It follows that a detached bronchogenic cyst can be found in these regions, such as at the bifurcation of the trachea (most common), the posterior mediastinum, the chest wall [Citation4]. The cyst may also abandon the diaphragm to invade the abdominal cavity, and end intraperitoneally or extraperitoneally, thus found in the liver or the adrenal gland [Citation4].
Ectopic locations of bronchogenic cysts such as in the neck (submental, thyroid) can be explained by the fact that bifurcation of the foregut toward trachea and esophagus takes place very close to the pharyngeal apparatus of the embryo. As per Bremer [Citation4], the lung buds—after bifurcation of the tracheal bud—can be considered the most caudal pair of pharyngeal pouches. The neighborhood with pharyngeal arches and pouches explains how a bronchogenic cyst may migrate next doors into the midline neck and thyroid gland.
The cranial (neck) and caudal (below the diaphragm) locations of bronchogenic cysts are better understood through the above-simplified explanations. We read elsewhere hypotheses such as that the neck location of these cysts can be explained by their trajectory through a plane parallel to the trachea [Citation3]. However, the mediastinum can only continue to the splanchnic compartment of the neck [Citation5]; thus, this hypothesis cannot explain submental cysts or even cysts in the thyroid (migration in the deep plane does not mean fusion with the thyroid anlage). To explain the subcutaneous position in the neck, it was hypothesized that bronchogenic cysts follow a plane through the sternal bars before their fusion [Citation3]. More imagination requires the repeated suggestion that the cysts are found intrabdominally because of the presence of open pleuroperitoneal canals [Citation6,Citation7].
In conclusion, the surgeon should better stick with the understandable etiologies for the embryogenesis of bronchogenic cysts. These are usually found in good old books, such as Congenital Anomalies of the Viscera by L. J. Bremer (1957) [Citation4], or Embryology for Surgeons by S.W. Gray and J. E. Skandalakis (1972, 1994) [Citation8,Citation9]. Otherwise, as my mentor J. E. Skandalakis used to say, “Embryology is full of ‘if’ and ‘perhaps’,” especially when it comes to explanations of rare malformations.
Declaration of Interest
The author has no competing interests to declare.
References
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- Skandalakis JE, Gray SW. Embryology for surgeons: the embryologic basis for the treatment of congenital anomalies. 2nd ed. Baltimore: Williams & Wilkins; 1994.