SciELO - Scientific Electronic Library Online

 
vol.15 número2ANALISIS CUANTITATIVO Y TOPOGRAFICOS DEL AZUFRE EN LA ZONA PELUCIDA DE LOS OVOCITOS DE RATON, HAMSTER Y CONEJO índice de autoresíndice de materiabúsqueda de artículos
Home Pagelista alfabética de revistas  

Servicios Personalizados

Articulo

Indicadores

  • No hay articulos citadosCitado por SciELO

Links relacionados


Revista chilena de anatomía

versión impresa ISSN 0716-9868

Rev. chil. anat. v.15 n.2 Temuco  1997

http://dx.doi.org/10.4067/S0716-98681997000200001 

ANATOMICAL STUDY ON THE VARIATIONS OF THE ANTERIOR BELLY OF
THE DIGASTRIC MUSCLE

MUSCULO DIGASTRICO: ESTUDIO ANATOMICO SOBRE LAS VARIACIONES
DE SU VIENTRE ANTERIOR

 

Jesús Carlos Andreo
João Adolfo Caldas Navarro
João Lopes Toledo Filho

Departamento de Morfologia - Anatomia - da Faculdade de Odontologia de Bauru da Universidade de São Paulo (USP). Brasil.

SUMMARY: Several investigators have recently emphasized the need of a better knowledge of the normal anatomy and variations of the anterior belly of the digastric muscle. Hypertrophy of the muscle mass, and variation in number and site of insertion of this muscle in relation to the midline may interfere with its functional behavior. Upon clinical or imaging examination, these variations may occasionally be confused with an infarcted submental lymph node. Some investigators have suggested that these variations may be involved in asymmetrical movements of the temporomandibular joint. We report here 5 cases detected during routine dissection in order to alert the professionals to the incidence of this type of variation. The volume of the anterior belly of the digastric muscle in some cases is quite developed, considerably approaching the midsagittal plane. Five cases of variation in number of anterior bellies were detected. In 3 of them only one accessory belly was observed, located in the right antimere in 2 cases and in the left antimere in the third. In 1 case 2 accessory bellies were detected, one in each antimere, although both of them crossed the midsagittal plane in an Xshaped pattern. In another case, 2 accessory bellies were detected in a single antimere, one of them more developed and parallel to the normal belly, and the other less developed and oblique in relation to the normal belly. In view of the multiple anatomical variations and their possible repercussions on the functional behavior of this important suprahyoid muscle, we suggest that all variations should be described and, if possible, that all clinical cases should be documented.

KEY WORDS: 1. Anatomy; 2 . Digastric muscle; 3. Muscles of the neck; 4. Suprahyoid muscles; 5. Muscles of mastication.

  INTRODUCTION

The knowledge of anatomy and its variations is very important for the use of modern methods of diagnostic imaging, as pointed out by several investigators (LARSSON & LUFKIN, 1987; NORTON, 1991; SARGON & CELIK, 1994).

According to NORTON , anatomical variations of the digastric muscles were described as early as in the past century by MORESTIN (1894), TESTUT (1894), SIRAUD (1895), PETRINI (1898), and VANNUCCI (1899), and later by WAERN (1935). However, it was only recently that this topic attracted greater attention due to its importance for the diagnosis of diseases of the mouth floor and of the submandibular and submental regions.

An increased muscle mass along the midline of the submentonian region can be identified by computer tomography as a pseudomass of the mylohyoid muscle and can only be differentiated by enhanced contrast or by magnetic resonance (NORTON). An accessory belly of the digastric muscle crossing the submental trigone may be erroneously identified as an infarcted submental lymph node both by computer tomography and magnetic resonance, unless the radiologist or surgeon is aware of the possibility of this anatomical variation.

SARGON & CELIK agree with these inves-tigators when they state that some types of variation of the digastric muscle may be confused with pathological conditions, and for this reason knowledge of the muscle anatomy and of the variations of the mouth floor is useful for the evaluation of the base of the skull by magnetic resonance and computer tomography. Some investigators have pointed out the possibility that these anomalous insertions of the digastric muscle are involved in asymmetrical mandibular movements of the temporo-mandibular joint (STOCKSTILL et al., 1991).

In view of the importance of the anatomical variations of the anterior belly of the digastric muscle, in the present report we compare the data obtained in the study of this muscle with those in the literature in order to provide data that may aid imaging diagnosis.

MATERIAL AND METHOD

Important aspects of the digastric muscle, such as an anatomical variations, were studied by macro and mesoscopic dissection using a DF Vasconcellos M900 surgical microscope with a 12.5 mm eyepiece and a 200 mm objective. Documentation was obtained by taking slides and photographs with a Nikon camera fitted with a NikkorMedical 110 mm lens.

RESULTS

In some cases, the anterior belly of the digastric muscle was quite voluminous, closely approaching the midsagittal plane (Figure 1). Five cases of variations in the number of anterior bellies were observed. Only one accessory belly was present in 3 and was located in the right antimere in 2 of them (Figures 2 and 3), and in the left antimere in the third (Figure 4). Two accessory bellies were found in 1 case, one in each antimere, but both of them crossing in an Xshaped pattern along the midplane (Figure 5). Two accessory bellies in a single antimere were detected in another case, one of them more developed and parallel to the normal belly, and the other less developed and oblique in relation to the normal belly (Figure 6).

DISCUSSION

According to SICHER & DU BRUL (1991), anatomical variations of the digastric muscle are frequent and are usually limited to the anterior belly of the muscle. A survey of the literature showed that some investigators present a generic description of the topic, considering that the anterior bellies of the digastric muscle may anastomose through accessory muscle fasciculi (APRILE et al., 1971). Other investigators have reported more detailed descriptions, stating that the anterior belly may fuse (ORTS LLORCA, 1959; TESTUT & JACOB, 1961) or that a supernumerary fasciculus is inserted into the median raphe (cases not detected in the present study) or into the digastric fossa, as illustrated in Figures 2, 3, 4, 5 and 6 (TESTUT & JACOB).

According to some investigators (SICHER & DU BRUL, 1991), the most frequent variations in relation to the typical format are oblique connections between the two bellies, as shown here in Figure 5, or two accessory bellies parallel to the anterior bellies of the digastric muscle, as shown here in Figure 6 (NORTON).

There are also descriptions of an accessory belly of the anterior belly of the digastric muscle in only one of the antimeres, as can be seen here in Figures 3 and 4 (SATO et al., 1987; MICHNA, 1989; CELIK et al., 1992; SARGON & CELIK, 1994).

LARSSON & LUFKIN (1987) described an accessory belly of the anterior belly of the digastric muscle crossing the midsagittal plane, as shown here in Figure 2. These authors also reported a case of absence of the anterior belly of the digastric muscle, which was not found by us.

Considering the multiple anatomical variations of the anterior belly of the digastric muscle and the possibility that they may interfere with the functional behavior of this important suprahyoid muscle, we suggest that all variations be reported and, if possible, that clinical cases be documented.

Figures 1, 2, 3, 4, 5 and 6 - Anterolateral region of the neck. Suprahyoid region: a) body of the mandible; b) vasculonervous mylohyoid pedicle; c) submandibular gland duct; d) submandibular gland; e) hypoglossus nerve; f) anterior belly of the digastric muscle; g) accessory belly of the digastric muscle. Infrahyoid region: h) infrahyoid muscles; i) thyroid cartilage.

RESUMEN: Actualmente, algunos investigadores han alertado sobre la necesidad de un conocimiento más profundo, de la anatomía normal y variaciones del vientre anterior del músculo digástrico. La hipertrofia en la masa muscular, la variación en el número y local de inserción de ese músculo en relación a la línea media, puede interferir en su comportamiento funcional. Algunas veces, en el examen clínico o a través de imágenes esas variaciones pueden ser confundidas con linfonodos submentonianos inflamados. Algunos autores han sugerido que tales variaciones pueden estar comprometidas con movimientos mandibulares asimétricos de la ATM. El relato de cinco casos encontrados por los autores, en disecciones de rutina, están siendo publicados con el objetivo de comunicar a los profesionales sobre la incidencia de este tipo de variaciones. El volumen del vientre anterior del músculo digástrico en algunos casos se presenta bastante desarrollado, aproximándose mucho al plano sagital mediano. En cuanto al número de vientres anteriores fueron encon trados 5 casos de variaciones. En 3 de ellos se observó apenas un vientre accesorio, en dos casos estaban en el lado derecho y en el otro, en el izquierdo. En un caso fueron encontrados dos vientres accesorios, uno e cada lado. Sin embargo, ambos cruzaban el plano sagital medio en X. En otro caso fueran encontrados dos vientres accesorios en un único lado, donde uno era mas desarrollado y estaba paralelo al vientre normal y el otro menos desarrollado oblicuo al vientre normal. Considerando la multiplicidad de variaciones anatómicas y la posibilidad que éstas influyeran en el comportamiento funcional de este importante músculo suprahioideo, sugerimos que todas las variaciones deben ser divulgadas y, si es posible, que los casos clínicos sean documentados.

PALABRAS CLAVE : 1. Anatomía; 2. Músculo digástrico; 3. Músculos del cuello; 4. Músculos suprahioideos; 4. Músculos masticadores.

REFERENCES

APRILE, H.; FIGUN, M. E. & GARINO, R.R. Anatomia odontológica. 5a. ed. Buenos Aires, El Ateneo, 1971.         [ Links ]

CELIK, H.; YILMAZ, E.; ATASEVER, A.; DURGUN, B. & TANER, D. Bilateral anatomical anomaly of the anterior bellies of digastric muscles. Kaibogaku Zasshi. 67(5):6501, 1992.         [ Links ]

LARSSON, S. G. & LUFKIN, R. B. Anomalies of digastric muscles: CT and MR demonstration. J Comput Assist Tomogr., 11(3):4225, 1987.         [ Links ]

MICHNA, H. Anatomical anomaly of human disgastric muscles. Acta Anat., 134:2634, 1989.         [ Links ]

MORESTIN (1894) apud NORTON, M. R. op cit.

NORTON, M. R. Bilateral acessory digastric muscles. Brit. J. oral Maxillofac. Surg., 29(3):1678, 1991.         [ Links ]

ORTS LLORCA, F. Anatomía humana. 2a. ed. Barcelona, Científico-Medica, 1959. V. 1. p. 813.         [ Links ]

PETRINI (1898) apud NORTON, M. R. op cit.

SARGON, M. F & CELIK, H. H. An abnormal digasrtric muscle with three bellies. Surg Radiol Anat., 16: 21516, 1994.         [ Links ]

SATO, Y.; UENO, R. & SATO, T. A consideration of the normal and abnormal human suprahyoid and infrahyoid musculature. Okajimas Folia Anat Jpn., 64 (1):1738, 1987.         [ Links ]

SICHER, H. & DU BRUL, E. L. Anatomia oral. 8a. ed. São Paulo, Artes Médicas, 1991. p. 1045.         [ Links ]

SIRAUD (1895) apud NORTON, M. R. op cit.

STOCKSTILL, J. W.; HARN, S. D. & UNDERHILL, T. E. Clinical implications of anomalous muscle insertion relative to jaw movement and mandibular dysfunction: tha anterior belly of the digastric muscle in a cadaver. J. Craniomand Disord., 5(1):64-70, 1991.         [ Links ]

TESTUT (1894) apud NORTON, M. R. op cit.

TESTUT, L. & JACOB, O. Tratado de anatomía topográfica. 8a. ed. Barcelona, Salvat, 1961. V.1. p. 833.         [ Links ]

VANNUCCI (1899) apud NORTON, M. R. op cit. WAER (1935) apud NORTON, M. R. op cit.

Dirección para correspondencia:
Prof.
Dr. Jesús Carlos Andreo
Departamento de Morfologia
Anatomia Faculdade de Odontologia de Bauru
Universidade de São Paulo (USP).
Al. Dr.Octávio Pinheiro Brisolla 975
CEP 17043101
Bauru S.P. BRASIL

Recibido : 12-02-1997
Aceptado : 30-07-1997