An unusual variant of the atlantomastoid muscle.

Knowledge of anatomical variations can be of use to clinicians and surgeons when, for example, viewing images of a patient or performing operations. Such knowledge can minimise the risk of iatrogenic complications. Herein, we present a case of a variant atlantomastoid muscle. The muscle was identified on the left side in an adult cadaver. The muscle's measurements and anatomical relationships are presented as well as a review of salient literature. We hope that increased knowledge of anatomical variants in the suboccipital region can improve patient care.

Development, maturation, and growth of the myodural bridge within the posterior atlanto-axial interspace in the rat.

The myodural bridge (MDB) complex are fibrous bridges that functionally connect the spinal dura mater to the suboccipital musculature. Previously, we described the maturational sequence of the MDB within the posterior atlanto-occipital interspace of the rat. The present paper describes the morphology and developmental maturation of the MDB within the posterior atlanto-axial interspace of the rat. In the present study, E18 embryonic rats, newborn rats, and adult rats were selected to evaluate the development and growth of the MDB. Within the posterior atlanto-axial interspace of the rat, the fibers of the MDB and its associated muscles, in the embryonic rat, were observed to be scarce and lightly stained. In contrast, these same structures observed in the postnatal rat were quite apparent and robustly stained. After birth, it was observed that MDB originated from the rectus capitis dorsal major muscle, extended forward and downward, and finally merged with the posterior atlanto-axial membrane. As the rats developed and matured, the observed MDB fibers passing through the posterior atlanto-axial interspace appeared denser and more organized. This study evidenced that the MDB fibers within the posterior atlanto-axial interspace were primarily composed of type I collagen fibers in the postnatal rat. By observing the suboccipital region, we are able to hypothesize that the MDB complex plays a key role in maintaining the subdural space located within the upper cervical segment during growth and development. This study provides a morphological basis for future research on the function of the MDB complex.

The myodural bridge complex defined as a new functional structure.

PURPOSE: The connective tissue between suboccipital muscles and the cervical spinal dura mater (SDM) is known as the myodural bridge (MDB). However, the adjacent relationship of the different connective tissue fibers that form the MDB remains unclear. This information will be highly useful in exploring the function of the MDB. METHODS: The adjacent relationship of different connective tissue fibers of MDB was demonstrated based upon three-dimensional visualization model, P45 plastinated slices and histological sections of human MDB. RESULTS: We found that the MDB originating from the rectus capitis posterior minor muscle (RCPmi), rectus capitis posterior major muscle (RCPma) and obliquus capitis inferior muscle (OCI) in the suboccipital region coexists. Part of the MDB fibers originate from the ventral aspect of the RCPmi and, together with that from the cranial segment of the RCPma, pass through the posterior atlanto-occipital interspace (PAOiS) and enter into the posterior aspect of the upper cervical SDM. Also, part of the MDB fibers originate from the dorsal aspect of the RCPmi, the ventral aspect of the caudal segment of the RCPma, and the ventral aspect of the medial segment of the OCI, enter the central part of the posterior atlanto-axial interspace (PAAiS) and fuse with the vertebral dura ligament (VDL), which connects with the cervical SDM. CONCLUSIONS: Our findings prove that the MDB exists as a complex structure which we termed the 'myodural bridge complex' (MDBC). In the process of head movement, tensile forces could be transferred possibly and effectively by means of the MDBC. The concept of MDBC will be beneficial in the overall exploration of the function of the MDB.

Anatomical parameters of the rectus capitis posterior major and obliqus capitis inferior muscles based on an oblique sagittal magnetic resonance scan method / Parámetros anatómicos de los músculos recto posterior mayor de la cabeza y oblicuo mayor de la cabeza basados en un método oblicuo sagital de exploración por resonancia magnética

The deep suboccipital muscles has been shown to connect the spinal dura mater via dense connective tissue termed the myodural bridge (MDB). The MDB has both physiological and clinical implications. Data on morphological and imaging anatomical parameters of the deep suboccipital muscles are scare. In this study, T2-weighted images of rectus capitis posterior major (RCPma) and obliqus capitis inferior (OCI) of 109 healthy adults were obtained by 0-degree sagittal and 30-degree oblique sagittal continuous MRI scanning of the head and neck of the subjects. Sectional area parameters of the RCPma and the OCI were measured. The 0-degree sagittal section was measured with 5 mm bias from the median sagittal plane, the sectional area of the RCPma was 186.34± 55.02 mm2 on the left, and 202.35± 59.76 mm2 on the right. The sectional area of OCI was 221.72± 68.99 mm2 on the left, and 224.92± 61.34 mm2 on the right; At the section with 30-degree bias from the oblique sagittal plane, the sectional area of RCPma was 183.30± 42.24 mm2 in males, and 133.05± 26.44 mm2 in females. The sectional area of OCI was 254.81± 46.20 mm2 in males, and 167.42± 27.85 mm2 in females. Significant sex difference exists in the sectional areas of the RCPma and OCI, the values of the male subjects were predominantly larger (P < 0.05), however there were no age- related significant difference. The sectional area of RCPma is bilateral asymmetric, the RCPma on the right side is larger than that of the left side (P < 0.05), but the OCI is bilaterally symmetric (P >0.05). The MRI image features, imaging anatomical data and sexual dimorphism of the RCPma and the OCI are presented in this study. This imaging anatomical data will be useful for functional and clinical studies on the RCPma, OCI, and the MDB.

Se ha demostrado que los músculos suboccipitales profundos conectan la duramadre espinal a través del tejido conectivo denso denominado puente miodural (PMD). El PMD tiene implicaciones tanto fisiológicas como clínicas. Los datos sobre los parámetros anatómicos y morfológicos y de imagen de los músculos suboccipitales profundos son alarmantes. En este estudio, se obtuvieron imágenes ponderadas en T2 del músculo recto posterior mayor (RCPma) y del músculo oblicuo mayor de la cabeza (OCI) de 109 adultos sanos, mediante una exploración de la cabeza y el cuello sagital de 0 grados y sagital oblicua de 30 grados. Se midieron los parámetros de área seccional del RCPma y el OCI. La sección sagital de 0 grados se midió con un sesgo de 5 mm desde el plano mediano, el área de la sección de la RCPma fue 186,34 ± 55,02 mm2 a la izquierda y 202,35 ± 59,76 mm2 a la derecha. El área seccional de OCI fue 221.72 ± 68.99 mm2 a la izquierda y 224.92 ± 61.34 mm2 a la derecha. En la sección de 30 grados desde el plano sagital oblicuo, el área de la sección de RCPma fue de 183.30 ± 42.24 mm2 en los hombres, y 133.05 ± 26.44 mm2 en las mujeres. El área seccional de OCI fue de 254.81 ± 46.20 mm2 en varones y 167.42 ± 27.85 mm2 en mujeres. Existe una diferencia significativa según el sexo en las áreas seccionales de la RCPma y la OCI, los valores de los sujetos masculinos fueron predominantemente mayores (P <0.05). Sin embargo, no hubo diferencia significativa relacionada con la edad. El área de la sección de RCPma es bilateral asimétrica, la RCPma en el lado derecho es más grande que la del lado izquierdo (P <0.05), pero el OCI es bilateralmente simétrico (P> 0.05). Las características de la imagen de resonancia magnética, los datos anatómicos de imágenes y el dimorfismo sexual de la RCPma y la OCI se presentan en este estudio. Estos datos anatómicos de imágenes serán útiles para estudios funcionales y clínicos en RCPma, OCI y PMD.

Anatomical parameters of the rectus capitis posterior minor muscle based on a new magnetic resonance scan method / Parámetros anatómicos del músculo recto posterior menor de la cabeza basado en un nuevo método de escaner con resonancia magnética

The past findings confirm that the Rectus Capitis Posterior minor (RCPmi) is connected to the cervical spinal dura mater via the Myodural Bridge (MDB) through the posterior antlanto-occipital interspace. It is hypothesized to perform some functions. Furthermore, some clinical studies found that the pathology of RCPmi might be related to chronic headaches. But few studies were related to the morphological parameters of the RCPmi. It would be conducive to performing clinical researches on the RCPmi and MDB. To explore the optimal section for measuring the RCPmi by MRI and provide imaging anatomy parameters of the RCPmi for clinical research. The RCPmi was measured in the dissection of 10 formalin-fixed cadaver specimens. The morphological parameters of the RCPmi were obtained. Based on these parameters, T2-weighted images of the RCPmi were collected from 109 healthy adults by using the MRIs with different oblique sagittal scanning angles. The parameters of length and area of the RCPmi on the scanning sections were measured using MRI workstation and Mimics software. The length of RCPmi reached a maximum at 30 degrees scanning leaned from the posterior median line through the dens of the axis in oblique sagittal section. At this scanning section, the length of RCPmi was 21.2 ± 2.6 mm in males and 19.3 ± 2.4 mm in females and the area of RCPmi was 91.9 ± 27.2 mm2 in males and 73.3 ± 22 mm2 in females. These parameters of RCPmi were present with significant gender differences (P < 0.05) but was not age related. Thirty degrees leaned from the median line was suggested to be the optimum scanning angle to display the RCPmi in oblique sagittal section. The reference values of length and area of the RCPmi were established for studies of hypertrophy or amyotrophy of the RCPmi.

Hallazgos previos confirman que el músculo rector posterior menor de la cabeza (mRPMC) está conectado a la duramadre cervical por medio del puente miodural (PMD) a través del espacio intermedio antlanto-occipital posterior. Se plantea la hipótesis de su capacidad para realizar algunas funciones. Además, estudios clínicos encontraron que la patología del mRPMC podría estar relacionada con dolores de cabeza crónicos. Sin embargo, pocos estudios se relacionaron con los parámetros morfológicos del mRPMC. Se buscará realizar investigaciones clínicas sobre el mRPMC y el PMD, además de explorar la sección óptima que permita medir el mRPMC por resonancia magnética (RM) y que permita obtener la imagen adecuada para la identificación de los parámetros anatómicos del mRPMC en la investigación clínica. Se midió el mRPMC durante la disección de 10 especímenes, correspondientes a cadáveres fijados con formalina. Se obtuvieron los parámetros morfológicos del mRPMC. Basándose en estos parámetros, se estudiaron imágenes ponderadas en T2 del mRPMC de 109 adultos sanos, utilizando las resonancias magnéticas con diferentes ángulos de exploración sagital oblicua. Los parámetros de longitud y área del mRPMC en las secciones de exploración se midieron utilizando la estación de trabajo del equipo de RM y el software Mimics. La longitud del mRPMC alcanzó un máximo de 30 grados de exploración, inclinado desde la línea mediana posterior, a través del eje en la sección sagital oblicua. En esta sección la longitud del mRPMC fue 21,2 ± 2,6 mm en los hombres y 19,3 ± 2,4 mm en las mujeres, y el área del mRPMC fue 91,9 ± 27,2 mm2 en los hombres y 73,3 ± 22 mm2 en las mujeres. Se observaron diferencias significativas de sexo en estos parámetros del mRPMC (P <0,05) sin embargo estos no estaban relacionados con la edad. Se sugirieron 30 grados inclinados a partir de la línea mediana como el ángulo óptimo de exploración para mostrar el mRPMC en la sección sagital oblicua. Los valores de referencia de longitud y área del mRPMC se establecieron para estudios de hipertrofia o amiotrofia del mRPMC.