Study of Digastric Muscle in Brazilian Individuals / Estudio del Músculo Digástrico en Individuos Brasileños

SUMMARY: Correct detailed description of the anatomy of the digastric muscle (DM) in different populations should be carried out to improve the teaching of anatomy, avoid misinterpretations and help to avoid intercurrences during surgical procedures in the region. The aim of this study was to carry out a study of the DM in adult Brazilian individuals. The sample consisted of 50 DM from adult individuals (22 right side and 28 left side) fixed in 10 % formaldehyde. The morphology of the DM was observed, identifying possible anatomical variations; these were characterized and classified according to the number of the muscle bellies, direction of the fibre, and points of origin and insertion. The morphometric measurements were performed using a digital calliper. Student's t-test for dependent samples was used to measure differences between sides; one-way ANOVA was used to analyse the different classifications, and the chi-squared test to analyse qualitative variables, with significance threshold of 5 %. The anterior belly of the DM was classified as Type I in 28 samples (56 %), Type II in 20 (40 %) and Type III in 2 (4 %). The mean length was 37.8 mm, width 12.1 mm and thickness 5.39 mm, with no statistically significant differences found for these variables. The intermediate tendon of the DM was classified as Type I in 31 samples (62 %), Type II in 10 (20 %) and Type III in 9 (18 %); its mean total length was 45.1 mm. The posterior belly of the DM was Type I in 50 samples (100 %), with mean length 70.8 mm and width 8.15 mm. Anatomical variations of the DM, particularly its anterior belly, in Brazilian adults are very frequent. They must therefore be carefully identified to help avoid intercurrences during surgical procedures in the region, and to help correct evaluation of swollen lymph nodes in the submental triangle.

Con el propósito de ayudar en la enseñanza de la Anatomía se debe realizar una descripción correcta y detallada del músculo digástrico (MD), evitando malas interpretaciones y contribuyendo a evitar intercurrencias durante procedimientos quirúrgicos en la región. El objetivo de este estudio fue realizar un estudio del MD en individuos brasileños. Fueron utilizadas 50 muestras de MD de individuos adultos (22 del lado derecho y 28 del lado izquierdo) fijadas en formaldehido al 10 %. Se analizó la morfología del MD, identificando las posibles variaciones anatómicas, que fueron clasificadas según el número de vientres musculares, dirección de las fibras y lugar de origen e inserción. Para el análisis estadístico las medidas fueron realizadas con un paquímetro digital. Para el análisis estadístico fueron utilizadas las pruebas de t de Student, ANOVA de una vía para variables continuas y la prueba de chi-cuadrado con ajuste de Bonferroni para las variables categóricas. Se utilizó el software SPSS v. 28.0, considerándo umbral de significación de 5 %. El vientre anterior del MD se clasificó como Tipo I en 28 muestras (56 %), como Tipo II en 20 (40 %) y como Tipo III en 2 (4 %). El promedio de longitud fue de 37,8 mm, la anchura de 12,1 mm y el espesor de 5,39 mm, no siendo encontradas diferencias estadísticas significativas para estas variables. El tendón intermedio del MD fue Tipo I en 31 muestras (62 %), Tipo II en 10 (20 %) y Tipo III en 9 (18 %). El promedio de su longitud total fue de 45,1 mm. El vientre posterior del MD fue de Tipo I en 50 muestras (100 %), con promedio de longitud de 70,8 mm y de ancho de 8,15 mm. Las variaciones anatómicas del MD, particularmente de su vientre anterior, son muy frecuentes en brasileños adultos, por lo que deben ser identificadas detalladamente contribuyendo a evitar intercurrencias durante los procedimientos quirúrgicos en la región y también para propiciar la correcta evaluación de las adenopatías del espacio submentoniano.

The Digastric Muscle: Its Anatomy and Functions Revisited / El Músculo Digástrico: Revisión de su Anatomía y Funciones

SUMMARY: As one of the suprahyoid muscles, the digastric muscle is characterized by two separate bellies of different embryologic origins. The origin of the anterior belly is the digastric fossa, while the origin of the posterior belly is the mastoid notch. They share a common insertion: the intermediate tendon. When the digastric muscle contracts, the hyoid bone is raised. Opening of the jaw and swallowing of food boli are associated with digastric muscle activity. This review discusses the general anatomic features of the digastric muscle and its variation, primary functions, and clinical implications focused on surgical reconstruction and rejuvenation.

Como uno de los músculos suprahioideos, el músculo digástrico se caracteriza por dos vientres separados, de diferentes orígenes embriológicos. El origen del vientre anterior es la fosa digástrica, mientras que el origen del vientre posterior es la incisura mastoidea. Comparten una inserción común, El tendón intermedio. Cuando el músculo digástrico se contrae, el hueso hioides se eleva. La apertura de la mandíbula y la deglución del bolo alimenticio se asocian con la actividad del músculo digástrico. Esta revisión analiza las características anatómicas generales del músculo digástrico y su variación, funciones primarias e implicaciones clínicas centradas en la reconstrucción y el rejuvenecimiento quirúrgico.

Anatomical variations of the anterior belly of the digastric muscle / Variaciones anatómicas del vientre anterior del músculo digástrico

A routine dissection of the digastric muscle reflected that it originated by two muscle bellies namely. the anterior and posterior belly which are connected by an intermediate tendon (IT). These bellies originated from the mastoid process of the temporal bone and the digastric fossa of the mandible respectively. The digastric muscle serves as an important surgical landmark in surgical interventions involving the submental area however, accessory bellies may interfere with surgical intervention in this area. Therefore, this study aimed to document the occurrence of the anatomical variations in the anterior belly of the digastric muscle (ABDM) in a selected number of cadaveric samples. Ten bilateral adult cadaveric head and neck specimens (n = 20) were macro-dissected in order to document the morphology of the digastric muscle. The accessory bellies in the ABDM was observed in 60 % of the specimens. Unilateral and bilateral variations were observed in 20 % and 30 % of the specimens, respectively. These accessory bellies originated in the digastric fossa, ABDM, IT and hyoid bone, and inserted into the mylohyoid raphe, mylohyoid muscle and hyoid bone. In addition, an anomalous main ABDM was observed in 10 % of the specimens inserting through a transverse tendon into the hyoid bone. Variations in the digastric muscle are common especially the accessory bellies, therefore, a comprehensive understanding of these anatomical variations could be of clinical importance to the surgeons during head and neck radiological diagnosis and surgical interventions.

Una disección de rutina del músculo digástrico refleja que se éste originaba por dos vientres musculares, anterior y posterior conectados por un tendón intermedio (IT). Estos vientres se originaban a partir del proceso mastoide del hueso temporal y de la fosa digástrica de la mandíbula, respectivamente. El músculo digástrico sirve como un hito quirúrgico importante en las intervenciones que involucran el área submental. Sin embargo, los vientres accesorios pueden obstaculizar la intervención quirúrgica en esta área. Por lo anterior, este estudio tuvo como objetivo documentar observaciones de las variaciones anatómicas en el vientre anterior del músculo digástrico (VAMD) en un número seleccionado de cadáveres. Las muestras consistieron en 10 cabezas y cuellos cadavéricos de individuos adultos, estudiadas bilateralmente (n = 20). Estas muestras fueron disecadas para documentar la morfología del músculo digástrico. Los vientres accesorios en el VAMD se observaron en el 60 % de los casos. Se observaron variaciones unilaterales y bilaterales en el 20 % y el 30 % de las muestras, respectivamente. Estos vientres accesorios se originaban en la fosa digástrica, VAMD, IT y hueso hioides, y se insertaban en el rafe milohioideo, el músculo milohioideo y el hueso hioides. Además, se observó un VAMD principal anómalo en el 10 % de las muestras que se insertaban a través de un tendón transversal en el hueso hioides. Las variaciones en el músculo digástrico son comunes, especialmente los vientres accesorios, por lo tanto, un conocimiento completo de estas variaciones anatómicas podría ser de importancia clínica durante el diagnóstico radiológico de cabeza y cuello y en las intervenciones quirúrgicas de la región.

Accessory Heads of Anterior Belly of Digastric Muscle in Korea / 계명의대학술지

The digastric muscle has two bellies and it has various variation in submental region. During dissection of a 79-year-old Korean female cadaver, bilateral variations at the anterior belly (AB) of the digastric muscle in submental region were shown. Two accessory bellies originated medial to the origin of the two normal ABs of the digastric muscle. They run medially and combined each other anterior to the median raphe of the mylohyoid muscle. In left side, AB of the digastric muscle was divided into two muscular bellies. Therefore, five bellies of ABs of the digastric muscle were found. This novel variation has not been described in the literature and this appearance will guide clinicians during surgical interventions and radiological diagnosis.

¿Músculo digástrico o músculo digastricomastoideo? / Digastric muscle or digastricmastoid muscle?

El músculo digástrico aparece mencionado en Terminología Anatomica con el código A04.2.03.006, pertenece al grupo de los músculos suprahioideos y está formado por dos vientres (latín: gaster) unidos por un tendón intermedio. El vientre anterior se origina en la fosa digástrica de la mandíbula y el vientre posterior en la incisura mastoidea del hueso temporal, ambos se insertan a través de una banda fibrosa, derivada de la capa pretraqueal de la fascia cervical profunda en el cuerpo y cuerno mayor del hueso hioideo. Los vientres anterior y posterior se originan del primer y segundo arco branquial respectivamente, siendo inervado el vientre anterior por el nervio milohioideo y el vientre posterior por el nervio facial. En su denominación el músculo digástrico hace referencia al origen del vientre anterior y a la clasificación muscular según forma, sin mencionar el origen de su vientre posterior. Es nuestro objetivo revisar este término y recomendar incluir en el nombre el origen "mastoideo" del músculo digástrico, denominándolo músculo digastricomastoideo. Este cambio se basa en el origen embriológico e inervación diferentes de ambos vientres y se relaciona con los objetivos propuestos por Terminologia Anatomica, que recomienda nombres descriptivos, informativos y armónicos con las estructura óseas relacionadas, favoreciendo la comunicación científica y la enseñanza-aprendizaje de la morfología.

The digastric muscle appears mentioned in Terminologia Anatomica with the code A04.2.03.006, it belongs to the group of the suprahyoid muscles and is formed by two bellys (latin: gaster) joined by an intermediate tendon. The anterior belly originates in the digastric fossa of the mandible and posterior belly in the mastoid notch of the tempral bone, both are inserted through a fibrous band, derived from the pretracheal layer of the deep cervical fascia on the body and greater horn of hyoid bone. Anterior and posterior bellys originates from the first and second arc gill respectively, the anterior belly being innervated by the mylohyoid nerve and the posterior belly by the facial nerve. In its name, the digastric muscle refers to the origin of the anterior belly and to the muscular classification according to form, not mentioning the origin of its posterior belly. The aim of this study was to review this term and recommend including in the name the "mastoid" origin of the digastric muscle, denominating it digastricomastoid muscle. This change is based on the different embryological origin and innervation of both bellys and is related to the objectives proposed by Terminologia Anatomica, which recommends descriptive, informative and harmonic names with related bone structures, favoring scientific communication and teaching-learning morphology.

Protection of the external branch of the superior laryngeal nerve in carotid endarterectomy / 中国脑血管病杂志

Objectives To investigate the methods of protecting external branch of the superior laryngeal nerve (EBSLN)in carotid endarterectomy and to observe the effect of using these methods in clinical surgery. Methods EBSLN (20 sides)of 10 heads of corpse were studied by using microanatomy from January 2013 to December 2013. The occurrence probability of EBSLN on the lower edge of posterior belly of digastric muscle,medial edge of external carotid artery and upper edge of superior thyroid artery in anatomy triangle was analyzed. The distances from the midpoint of the EBSLN to carotid bifurcation, mandibular angle and mastoid tip were measured. Sixty-five patients with carotid endarterectomy in Tianjin Huanhu Hospital from December 2013 to November 2014 were treated with the protective methods of the relevant EBSLN by using anatomy triangle as a mark. Whether the patients had injury symptoms of EBSLN were followed up after procedure. Results (1)The occurrence probability of 20-side EBSLN in anatomy triangle was 95%(19 sides). The midpoint of EBSLN in the anatomy triangle at the posterior mandibular angle was median 0. 34 (-1. 62 to 2. 43)cm,at the inferior mandibular angle was 1. 28 (-1. 33 to 3. 42) cm,at anterior mastoid tip was 2. 84 (0. 51 to 5. 14)cm,at inferior was 4. 51 (2. 82 to 6. 39)cm,and at anterior superior of the carotid bifurcation was 1. 64 (0. 57 to 3. 78)cm. (2)65 patients who underwent carotid endarterectomy used the protective methods of intraoperative EBSLN. There was no manifestation of EBSLN injury at 3 weeks to 9 months after procedure. Conclusion In carotid endarterectomy,taking an anatomic triangle as a symbol,it is no more than 2 cm of the anterior superior of carotid bifurcation during the separation process. As for the patients with higher or lower position of carotid bifurcation,in the range of crossing rear mandibular angle 0. 50 cm or below the mastoid tip 4. 50 cm for arterial separation should be avoided,and this can effectively protect EBSLN.

Anatomical variation of the anterior belly of the digastric muscle: case report and clinical implications

The digastric muscle is a suprahyoid muscle composed of two bellies connected by an intermediate tendon.This muscle participates in deglutition and mandibular movements. The anterior belly of the digastric muscleis localized superficially to the mylohyoid and deeply to the platysma muscle. During dissection of this regionof an embedded cadaver, an accessory anterior belly of digastric muscle was observed bilaterally. The accessorybellies were similar but not symmetrical. They were composed of two segments, one long and one short, onboth sides, and when observed together these appeared to form the letter “X”. The accessory fibers, on bothsides, originated from the anterior digastric muscle and inserted medially to the digastric fossa. Anatomicvariations of the digastric muscle may influence mastication and deglutition. Moreover, the accessory digastricmuscle affects diagnostic imaging and therapeutic procedures in head and neck surgery and must be consideredin procedures involving this area.

Reflejo C evocado en el músculo digástrico: un nuevo método para evaluar actividad wind-up trigeminal aplicable a principios activos de plantas medicinales / C-reflex evoked in the digastric muscle: a new method for evaluating trigeminal wind-up activity applicable to active principles of medicinal plants

Wind-up is a measure of nociceptive neurons synaptic potentiation and constitutes an important mechanism in the generation of central sensitization in chronic pain. At the spinal level, the C-evoked reflex in the bicep femoris muscle, by low frequency repetitive stimulation of the sural nerve, has enabled us to evaluate the wind-up of nociceptive neurons of the dorsal horn, and also the effect of antinociceptive drugs with a possible potential therapeutic value in chronic pain. In the present work, we electrophysiologically evaluated the trigeminal wind-up activity, utilizing as an experimental paradigm the evoked C-reflex in the Sprague-Dawley rat digastric muscle. The results obtained indicate that: (a) It is possible to evoke an electromyographic reflex in the digastric muscle by stimulation of C-fibers belonging to the third trigeminal branch; (b) It is possible to potentiate the trigeminal C-reflex with low frequency stimuli (wind-up) and (c) it is possible to depress the trigeminal wind-up with the μ-opioid agonist morphine and with the NMDA receptor antagonist, ketamine. We can conclude that the simple measurement of the trigeminal wind-up will facilitate future studies on the analgesic efficacy of new drugs in oro-facial chronic pain syndromes like migraine and with special emphasis on medicinal plant active principles.

El wind-up refleja la potenciación sináptica en neuronas nociceptivas y constituye un importante mecanismo en la generación de sensibilización central en dolor crónico. A nivel espinal, el reflejo C evocado en el músculo bicep femoris por estimulación repetitiva de baja frecuencia del nervio sural ha permitido evaluar la actividad wind-up en neuronas nociceptivas del cuerno dorsal, así como el efecto de drogas antinociceptivas con un posible potencial terapéutico en dolor crónico. En el presente trabajo evaluamos electrofisiológicamente la actividad wind-up trigeminal, utilizando como paradigma experimental el reflejo C evocado en el músculo digástrico de ratas Sprague-Dawley. Los resultados obtenidos indican que: (a) es posible evocar un reflejo electromiográfico en el músculo digástrico de la rata por estimulación de fibras C de la tercera rama del trigémino; (b) es posible potenciar el reflejo C trigeminal con estímulos de baja frecuencia (wind-up) y (c) es posible deprimir el wind-up trigeminal con el agonista μ-opioide morfina y con el antagonista NMDA, ketamina. Podemos concluir que la medición simple del wind-up trigeminal mediante el reflejo C evocado en el músculo digástrico facilitará futuros estudios sobre eficacia analgésica de nuevos fármacos en cuadros de dolor orofacial crónicos, como la migraña, con especial énfasis en los principios activos de plantas medicinales.

Bilateral variations of the head of the digastric muscle in Korean: a case report / 대한해부학회지

The digastric muscle, as the landmark in head and neck surgery, has two bellies, of which various variations have been reported. In the submental region of a 72-year-old Korean male cadaver, bilateral variations were found in the anterior belly of the digastric muscle. Two accessory bellies, medial to the two normal anterior bellies of the digastric muscle, ran posterior and medially, merging and attaching at the mylohyoid raphe of the mylohyoid muscle. The 3rd accessory belly originated from the right intermediate tendon and ran horizontally, merging the right lower bundle of the right accessory belly and inserted together. These accessory bellies had no connection with the left anterior belly. This unique variation has not been reported in the literature previously, and this presentation will guide clinicians during surgical interventions and radiological diagnoses.

Anatomic Variation of the Anterior Belly of Digastric Muscle and Positional Relationship between the Posterior Belly of Digastric and Stylohyoid Muscle / 체질인류학회지

The digastric muscle is located in the suprahyoid region which consists of anterior belly, intermediate tendon and posterior belly. This muscle is an important landmark when performing an operation of submental and upper neck region. Previous researches have reported about variations of the anterior and posterior belly of digastric muscle. However, there are few studies about the general morphology of the digastric muscle and the relationship with surrounding muscles. The purpose of this study was to analyze the morphology of the anterior belly of digastric muscle and confirm the topographic relationship between the digastric muscle and the stylohyoid muscle of Korean. Thirty-four cadavers (21 males, 13 females; mean age 65 years; range 24~89 years) were used in this study. The skin, subcutaneous tissues, superficial fascia and platysma were removed and a detailed dissection was performed, with extreme care being taken not to damage underlying the muscles of submental and upper neck region. After the dissections, all specimens were sketched and photographed. In 8 specimens, we observed the accessory bellies of the anterior belly of digastric muscle. We classified the accessory bellies into the crossover type (five specimens, 14.7%) that cross the mandibular raphe and unilateral type (three specimens, 8.82%). The findings resulting from observation of the anatomical relationship between the posterior belly of digastric and stylohyoid muscles, the posterior belly of digastric muscle perforated the stylohyoid muscle in 32 cases (65%) out of 49 sides. This case was subdivided into the belly of the stylohyoid muscle lean to the lateral (twenty-one specimens, 42.9%) or medial side (eleven specimens, 22.4%) of the posterior belly of digastric muscle. In 17 specimens (35%), the stylohyoid muscle existed on the medial side of the posterior belly of digastric muscle.

Localization of Motor Neuronal Cell Bodies Innervating the Digastric Muscle of the Rat Using Cholera Toxin B Subunit (CTB) / 대한해부학회지

We used cholera toxin B subunit (CTB) as a neural tracer to localize motor neuronal cell bodies innervating the digastric muscle. After CTB injection into the left anterior belly, CTB-labelled motor neuronal cell bodies were found in caudal half of the left and right trigeminal nucleus, the left and right facial nucleus, the accessory facial nucleus and the accessory trigeminal nucleus in pons. The total number of CTB-labelled motor neuronal cell bodies were 1,179+/-119.5 in the left pons and 246+/-61.8 in the right pons after CTB injections into the left anterior belly of digastric muscle. After CTB injection into left posterior belly, CTB-labelled motor neuronal cell bodies were found only in the left ventral part of accessory facial nucleus in caudal pons and the total number of CTB-labelled motor neuronal cell bodies were 270+/-29.3.

The Studies on Central Neural Axis to Innervate Rat Digastric Muscle / 대한해부학회지

The present study has been performed to investigate the neural axis of rat digastric muscle using viral tracer, pseudorabies virus. The upper nuclei to innervate digastric muscle were in accumbens nucleus, agran-ular insular cortex, central nucleus of amygaloid, lateral septal nucleus, frontal cortex, and subfornical organ etc, in telencephalon ; arcuate hypothalamic nucleus, lateral hypot-halamic area, medial preoptic nucleus, bed nucleus of stria terminalis, dorsomedial hypot-halamic nucleus, suprachiasmatic nucleus, paraventricular nucleus, and retrochiasmatic area etc, in diencephalon ; nucleus Darkschewitsch, interstitial nucleus of the medial logitudinal fasciculus, parabrachial nucleus, locus ceruleus, Kolliker-Fuse nucleus, trigeminal mesencephalic nucleus, red nucleus, substantia nigra, nucleus of posterior commissure, Edinger-Westphal nucleus, and dorsal raphe nucleus etc, in mesencephalon ; giganto-cellular reticular nucleus, raphe magnus nucleus, raphe pallidus nucleus, raphe obscuous nucleus, nucleus of solitary tracts, lateral reticular nucleus, parvocellular reticular nucleus, area postrema, facial nucleus, pontine reticular nucleus, pontine nucleus of trigeminal nerve and spinal nucleus of trigeminal nerve etc, in rhombencephalon. There are significant difference of numbers of PRV-Ba immunoreactive cells between right and left sides of brain in almost nuclei[P< 0.05]. But PRV-Ba immunoreactive cells were observed only ipsilaterally in accessory trigeminal motor nucleus, accessory facial nucleus and agranular insular cortex. Frontal cortex was the only area which were shown contralateral immunoreactivity. The results of this study provide anatomical support that both the cranial and caudal bellies are innervated by the same upper nuclei. The results also support the suggestion that the lower nuclei of digastric muscle, accessory trigeminal motor nucleus and accessory facial nucleus consist of somatotopic motor complex.