Introduction

The submental triangle, which is also known as the suprahyoid triangle, is part of the anterior triangle of the neck. The submental triangle is an unpaired triangle located between the hyoid bone and the mandible and medial to the anterior bellies of the digastric muscles. The borders of the submental triangle are the right and left anterior bellies of the digastric muscles laterally, with the mylohyoid muscles forming the floor of the submental triangle. The submental triangle contains important structures helping in the diagnosis process; for instance, the size of the submental lymph nodes can serve as a good indicator to determine whether the metastasis is present or not.

Structure and Function

The area between the hyoid bone and the mandible gets divided by the anterior belly of the digastric muscle into two triangles, which are the submental triangle and the submandibular triangle. An unpaired submental triangle has its borders by the anterior bellies of the digastric muscles. The submental tringle's apex at the chin and its base is the body of the hyoid bone. The mylohyoid muscles comprise the floor of the submental triangle. The submental triangle contains the submental lymph nodes, the mylohyoid nerve and veins drain into the anterior jugular vein.[1]

The anterior belly of the digastric muscle is attached to the digastric fossa and runs backward and downward to join the posterior belly of the digastric muscle. The joined tendon inserts into the body and the greater cornu of the hyoid bone. The space between the anterior belly of the digastric muscle and the posterior belly of the digastric muscle is the submandibular triangle. The space between the right anterior belly of the digastric muscle and the left anterior belly of the digastric muscle is the submental triangle.

The mylohyoid muscle is above the anterior belly of the digastric muscle. The mylohyoid muscle attaches to the mylohyoid line of the mandible and runs medially and downward to its insertion into the body of the hyoid bone. The right mylohyoid muscle and the left mylohyoid muscle are forming the floor of the submental triangle.

Embryology

The anterior belly of the digastric muscle starts embryonic development in the fourth week of pregnancy from the first pharyngeal arch.[1]

The mylohyoid muscle begins embryonic development in the fourth week of pregnancy from the first pharyngeal arch.

Blood Supply and Lymphatics

The submental lymph nodes are between the anterior bellies of the digastric muscle. The submental lymph nodes drain the floor of the mouth and the central area of the lower lip and the apex of the tongue. The submental lymph nodes drain into the submandibular lymph nodes and the deep cervical group which eventually drain into jugular lymph trunk.

The submental artery is the largest artery of the cervical branches of the facial artery. This artery emerges just after the facial artery exits from the submandibular gland. The submental artery delivers vascular supply to the skin of the submental area and the muscles that border the submental triangle — it anastomoses with the inferior alveolar artery and the sublingual artery. The submental artery runs between the mylohyoid muscle and the mandible and runs either deep or superficial relative to the anterior belly of the digastric muscle.[2]

Nerves

In some cases, there are communications of the mylohyoid nerve and the lingual nerve in the submental triangle. The mylohyoid nerve penetrates the mylohyoid muscle; then it runs parallel to the submental artery and the submental vein. The submental nerve runs beneath the submental artery and the submental vein.[3]

Muscles

The anterior belly of the digastric muscle, which forms the lateral borders of the submental triangle, is innervated by the inferior alveolar nerve which is a branch of the mandibular branch of the trigeminal nerve.[1]

The mylohyoid muscle, which forms the floor of the submental triangle, is innervated by the inferior alveolar nerve which is a branch of the mandibular branch of the trigeminal nerve.

Physiologic Variants

Researchers have found supernumerary muscle bundles in some cadavers that ran across the midline of the submental triangle. The mylohyoid nerve innervated these supernumerary muscle bundles. The researchers believed that these supernumerary muscle bundles were a combination of the anterior belly of the digastric muscle and the primordial remnants of the mylohyoid muscle.[4]

Surgical Considerations

A deficiency in the differentiation of the first pharyngeal arch is responsible for some variations of the anterior belly of the digastric muscle. These variations must be taken into consideration while performing surgery in the submental triangle region.[1]

While performing surgery to remove the anterior belly of the digastric muscle from the mylohyoid muscle, take the lingual nerve and the hypoglossal nerve into consideration because they often present in a complicated arrangement in both the submental triangle and the submandibular triangle.[3]

Clinical Significance

Masses confined to the submental triangle are diagnosed mainly by fine-needle aspiration, and the mainstay treatment is surgical excision except in cases of an abscess. Drainage and systemic antibiotics are the preferred treatment for an abscess. Histologically, there is a wide variety of the submental triangle mass entity including lipoma, sarcoidosis, non-Hodgkin lymphoma, hemangioma, abscess, dermoid cyst, and reactive lymphoid hyperplasia.[5]

The congenital lymphatic malformation can manifest as a submental triangle mass. The congenital lymphatic defect is suggested by clear fluid in the fine needle aspiration and low flow lesion in ultrasonography with Doppler.[6]

The submental triangle masses are complicated by dental presentations and cheilitis.[5]

The cut-off value of the size of the submental lymph nodes by measuring the short axis to the long axis ratio is 0.5.[7] The submental lymph nodes are commonly involved in metastasis of oral cavity cancer.[8] The submental lymph node is not a common site of tuberculous cervical lymphadenitis.[9]

There is a satisfactory level of the reproducibility for the submental lymph node measurements using 3-D ultrasound.[10] Ultrasonography is sensitive and specific for assessing the submental lymph nodes. Computed tomography scan is not particularly sensitive for determining the status of submental lymph nodes, but has specificity.[11]

The measurement of tongue-based activity is possible by recording electrical activity on the surface of the submental triangle. Electrical activity can be recorded using an electromyograph.