RESEARCH ARTICLEThe pterygospinous and pterygoalar ligaments and their relationship to the mandibular nerve: Application to a better understanding of various forms of trigeminal neuralgia
Introduction
Ossification of the pterygospinous and pterygoalar ligaments (i.e., bars) has been reported (Skrzat et al., 2005; Tubbs et al., 2009; Ryu et al., 2016; Pękala et al., 2017). In 1835, Civinini, an Italian anatomist, reported the lateral plate of the pterygoid process could approach the spine of the sphenoid bone and occasionally fuse with it (Civinini, 1835). Two years later, he described the pterygospinous ligament (Civinini’s ligament) that originates from the pterygoid fascia and extends from the posterior border of the lateral plate of the pterygoid process to the spine of the inferior surface of the greater wing. Of his specimens, 2–3% had an ossified ligament (Civinini, 1837; Peker et al., 2002). Ossification of this ligament, the so-called pterygospinous bar, results in a pterygospinous foramen (Civinini’s foramen). The nerve to the medial pterygoid muscle and related vessels can sometimes pass through this foramen (Peker et al., 2002).
Decades later, in 1862, Hyrtl, a German anatomist, described ossification of the pterygoalar ligament (Hyrtl’s ligament), the so-called the pterygoalar bar, which forms the pterygoalar foramen, masticatorium, crotaphitico-buccinatorium, or Hyrtl’s foramen (Hyrtl, 1862; Chouké and Hodes, 1951; Patnaik et al., 2001; Tubbs et al., 2009). Some of the motor fibers of the mandibular nerve (e.g., masseter and deep temporal nerves) might pass through this foramen (Antonopoulou et al., 2008). The pterygoalar ligament extends from the root of the lateral plate of the pterygoid process to the inferior surface of the greater wing, running beneath the foramen ovale (FO) to divide it into two parts or running lateral to the FO (Kavitha and Vasantha, 2014).
The incidence of the ossification of the pterygoalar ligaments is reported in up to 62.4% (Chouké, 1946, 1947; Tubbs et al., 2009; Rosa et al., 2010). Meanwhile, ossification of the pterygospinous ligament is reported in about 10% of the population (Civinini, 1837; Lepp and Sandner, 1968; Tebo, 1968; Peker et al., 2002; Das and Paul, 2007). Thus, ossification of the pterygospinous ligament is reported less frequently than that of the pterygoalar ligament (Jansirani et al., 2012).
Interestingly, most studies have used dry human skulls or bone tissue data obtained from computed tomographic images as opposed to performing cadaveric dissection of soft tissue structures. To date, only two studies have shown examples of the pterygoalar or pterygospinous ligaments in-situ (von Lüdinghausen et al., 2006; Komune et al., 2019). Therefore, the goal of this study was to present the positional relationship of the pterygoalar ligament/bar, pterygospinous ligament/bar, and branches of the mandibular nerve using cadaveric dissection to better understand the relationship of these structures and help elucidate potential extracranial V3 compression syndromes (Nomura et al., 2019).
Section snippets
Materials and methods
Thirty sides from fifteen Caucasian fresh frozen cadaveric heads (eight females and seven males), whose age at death ranged from 46 to 101 with a mean age of 80.4 ± 13.0 years, were used in this study. The mandibles were removed with preservation of the origin and belly of the medial pterygoid muscle. Next, the branches of the mandibular nerve (V3) in the infratemporal fossa were dissected. Any ligaments or bony bridges between the lateral plate of the pterygoid process and spine of the
Results
Based on the dissections, the pterygoalar ligament/bar and pterygospinous ligament/bar were defined as following (Fig. 1, Fig. 2):
The pterygospinous ligament/bar was defined as a ligament/bar between the lateral plate of the pterygoid process and inferior surface of the greater wing that runs medial to the main trunk of the mandibular nerve. The pterygospinous bar forms the pterygospinous foramen (Civinini’s foramen).
The pterygoalar ligament/bar was defined as a ligament/bar between the lateral
Discussion
The definitions of the pterygospinous and pterygoalar ligaments have been extremely vague in previous studies and prior studies on the ligaments were actually based on studies of the dry skull (Nayak et al., 2007; Daimi et al., 2011; Chakravarthi and babu, 2012; Devi et al., 2012; Natsis et al., 2014; Goyal and Jain, 2015). Additionally, in some previous studies, the terms “pterygoalar” and “pterygospinous” ligaments were confused thereby confounding the data. The results of our study indicate
Conclusions
This study provides a visual demonstration of the anatomical variations of the pterygospinous and pterygoalar ligaments and bars, and proposes a new classification based on the positional relationship between the ligament/bar and mandibular nerve branches. The authors believe this classification is simple to understand and use for future anatomical and clinical studies, and will provide an important standardization for future studies investigating the clinical implications of these structures
Conflict of interest
The authors received no funding or grants for this work from any organization or foundation. The authors declare that they have no conflicts of interest.
Ethical statement
The present study was performed in accordance with the requirements of the Declaration of Helsinki (64th WMA General Assembly, Fortaleza, Brazil, October 2013).
Acknowledgements
The authors would like to thank those who donated their body for the advancement of medical education and research. All the authors have read the manuscript and have approved this submission.
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