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This study was performed on 50 human embryos and fetuses between 7 and 17 weeks of development. Reichert's cartilage is formed in the second pharyngeal arch in two segments. The longer cranial or styloid segment is continuous with the otic capsule; its inferior end is angulated and is situated very close to the oropharynx.
The smaller caudal segment is in contact with the body and greater horn of the hyoid cartilaginous structure. No cartilage forms between these segments. The persistent angulation of the inferior end of the cranial or styloid segment of Reichert's cartilage and its important neurovascular relationships may help explain the symptomatology of Eagle's syndrome. Reichert's cartilage has been described as a continuous cartilaginous formation in the second pharyngeal arch and is the origin of several structures such as the styloid process of the temporal bone, the stylohyoid ligament and the lesser horns of the hyoid bone.
The styloid process and the stylohyoid ligament have been linked to Eagle's syndrome, which has a symptomatology characterized by the sensation of having a foreign body in the pharynx, causing difficult and painful swallowing and earache Eagle, , , , Studies on the aetiology of this syndrome have consistently reported an elongated styloid process Dwight, ; Balasubramanian, ; Lavine et al.
The length of the adult styloid process is variable, and according to Frommer , the mean length is 3. A longer styloid process has been interpreted as being due to calcification or ossification of the stylohyoid ligament Dwight, ; Graf, ; Balasubramanian, ; Lavine et al. Several theories have been proposed to explain calcification of the stylohyoid ligament. These include degenerative changes undergone by the fibres of the stylohyoid ligament Shenoi, , metaplasic alterations due to a traumatic stimulus that induces ossification of the stylohyoid ligament Steinman, , either due to an anatomical variation in which the stylohyoid ligament is ossified in early stages Steinman, or even to what Montalbetti et al.
These opinions still are considered controversial among authors who do not believe that there is enough objective evidence to support them.
The main objective of our study was to examine the morphology and relationships of Reichert's cartilage. This analysis is important as it may help to explain the symptomatology of Eagle's syndrome. Fifteen embryos and 35 human fetuses from the collection of the Embryology Institute of the Universidad Complutense de Madrid were studied. In the embryos, crown—rump length CRL ranged from In the fetuses, CRL ranged from 38 to mm weeks 9—17 of development Table 2.
All specimens were obtained from ectopic pregnancies or spontaneous abortions, and no part of the material gave indications of possible malformation. Frontal section. Haematoxylin—eosin staining. Cranial segment of Reichert's cartilage R , connected with the external carotid artery EC , lying between Reichert's cartilage and the stylohyoid muscle SH. The vasculonervous elements of the retrostyloid space are dorsal to Reichert's cartilage: glossopharyngeal nerve G , vagus nerve V , internal carotid artery IC , superior cervical ganglion S.
This adopts an elongated morphology and crosses the pharyngeal arch in a caudoventromedial direction. The cranial end of this cartilaginous structure is curved in a hook shape, is joined to the side of the otic capsule and resembles a prolongation from it Fig. Frontal sections. Azocarmine staining. A Hooked superior end of Reichert's cartilage R showing its continuity with the otic capsule OC ; due to the caudoventromedial direction of the cartilage, this is also sectioned caudally at the origin of the stylopharyngeal SP and stylohyoideal SH muscles.
C The start of the angulation of the inferior end of the cranial segment of Reichert's cartilage R. External carotid artery EC.
D Change in direction of the lower end of the cranial segment of Reichert's cartilage R orientated towards the oropharynx O. E Mesenchymal condensation MC , which continues caudally to the cranial segment of Reichert's cartilage clearly distinguished from the cartilage of the third pharyngeal arch greater horn of the hyoid cartilaginous structure GR.
Glossopharyngeal nerve G. Hypoglossal nerve H. F Human embryo BR-2 Caudal or hyoid segment of Reichert's cartilage RR in contact with the body B and the greater horn GR of the hyoid cartilaginous structure.
In the area where the external carotid artery passes through the space between Reichert's cartilage and the tendon where the stylohyoid muscle originates, Reichert's cartilage changes direction and becomes angulated with its end pointing towards the midline Fig. Caudal to this area, Reichert's cartilage is continuous with a mesenchymal cellular condensation where the cartilage has not formed.
This mesenchymal structure, which forms an extension of Reichert's cartilage, is separated from the angle of the mandible by the styloglossus muscle and can be clearly distinguished from the cartilage of the third pharyngeal arch Fig.
The mesenchymal condensation extends from Reichert's cartilage to the hyoid cartilaginous structure, finishing at the area where the body joins the greater horn. At the end of the embryonic period, the small portion of the mesenchymal structure that terminates in the hyoid cartilaginous formation has been changed into cartilage Fig. At the end of the embryonic period, the cartilage of the second pharyngeal arch adopts the following arrangement:. Cranial or styloid segment, longer and larger.
This cartilaginous segment has two ends: the superior end, joined to the otic capsule, and the inferior end, which is angulated. This clear angulation occurs where the cartilage is in close proximity with the external carotid artery Fig. Caudal or hyoid segment. This short cartilaginous segment terminates caudally in the hyoid cartilaginous structure between the body and the greater horn Fig. We found that between each segment no cartilage had formed. There is a mesenchymal condensation that joins the cranial segment with the caudal segment Fig.
Table 1 summarizes the most important results found for the embryonic period. During the fetal period, the superior end of the hook-shaped cranial or styloid segment of Reichert's cartilage is still continuous with the inferior extension of the otic capsule.
Both structures contribute to form the vertical portion of the facial nerve canal Fig. Caudally, this segment of Reichert's cartilage is related to the tympanic bone Fig.
This is followed by another segment that forms an angulation with the previous one that adopted a horizontal position Fig. This angulation, previously observed in the embryonic period, is located dorsally to the mandibular angle with its end pointing towards the oropharynx Fig. Its most important relationship in this region is with the glossopharyngeal nerve. Transverse sections. A Superior end of the cranial segment of Reichert's cartilage R , joined to the otic capsule OC and forming with this the vertical portion of the facial canal.
Facial nerve F. B Reichert's cartilage R is related to the tympanic part of the temporal bone T that separates it from Meckel's cartilage M. The stylopharyngeal muscle SP originates in Reichert's cartilage; dorsally is the posterior belly of the digastric muscle D.
C Angulated inferior portion of the cranial segment of Reichert's cartilage R , situated dorsal to the mandibular angle MA. The angulated end touches the pharyngeal wall PH. Greater horn of the hyoid cartilaginous structure GR. Meckel's cartilage M. Transverse section. Inferior portion of the cranial segment of Reichert's cartilage R. This presents a clear angulation dorsomedial to the mandibular angle MA.
The glossopharyngeal nerve G close to the stylopharyngeal muscle SP and with the angulated end of Reichert's cartilage R. Oropharynx O. Caudal segment of Reichert's cartilage RR that will form the lesser horn of the hyoid cartilaginous formation, situated between the body B and the greater horn GR.
Hyoglossus muscle HM. Lingual artery LA. Submandibular gland SG. Transverse section at the lateral suprahyoid region where Reichert's cartilage does not form. The hyoglossus muscle HM originates in the greater horn GR of the hyoid cartilaginous formation. The hypoglossus nerve H and the intermediate tendon of the digastric muscle DI run laterally to the hyoglossus muscle. The submandibular gland SG lies laterally to these structures.
Bielschowsky staining. A Cranial segment of Reichert's cartilage R that presents a less pronounced angulation. Lateral to the cartilage, the external carotid artery EC , the parotid gland P and the styloglossus muscle SO can be observed.
The stylopharyngeal muscle SP and the glossopharyngeal nerve G are medial to the cartilage. Pharynx PH. B Haematoxylin—eosin staining. Relationships between the cranial segment of Reichert's cartilage R and the external carotid artery EC and the external carotid nerves EN that surround it and with the glossopharyngeal nerve G situated between the end of the cartilage and the pharynx PH.
Stylopharyngeal muscle SP. The external carotid artery EC can be observed in the space formed between Reichert's cartilage R and the stylohyoid muscle SH situated laterally. At a post-conception age of 13 weeks, the angulation of the inferior end of the cranial or styloid segment may vary, giving rise to different degrees of angulation ranging from barely visible to extreme Table 2 ; Figs 3C,D and 4A,B.
The lengths of this segment are also variable, giving rise to cranial segments that are closer to or further from the mandibular angle.
The caudal segments of Reichert's cartilage are found on both sides of the cartilaginous hyoid body with which they are in contact, constituting the lesser horns Fig.
Between the cranial segment of Reichert's cartilage, which will form the styloid process, and the segment that will constitute the lesser horn, no cartilage was found to have formed in the second arch, except in one case which presented a unilateral continuous cartilage on the left side Table 2.
The mesenchymal condensation, which was present in the embryonic period, was observed at the start of the fetal period, but it then disappears and leaves no trace during the rest of the fetal period Fig. During the fetal period studied, Reichert's cartilage was found to have three noteworthy relationships:. With the pharynx, when angulation of the inferior end of the cranial or styloid segment persisted.
With the glossopharyngeal nerve. This nerve crosses medial to the inferior end of the cranial segment. With the external carotid artery. The artery surrounded by the external carotid nerves passes through the hiatus or space defined by Reichert's cartilage and the stylohyoid muscle.
ISBN 13: 9788481746556
ISBN 13: 9788481746556