Pirogov's Triangle

PIROGOV'S TRIANGLE, trigonum linguale, is a small triangular space in the lateral part of the suprahyoid region of the neck, formed below (posteriorly) by the tendon of the digastric muscle (m. digastricus), above by the hypoglossal nerve (n. hypoglossus), which passes obliquely together with the lingual vein, and internally (anteriorly) by the outer (posterior) edge of the mylohyoid muscle (m. mylo-hyoideus). The floor of the triangle is occupied by the hyoglossus muscle (m. hyo-glossus). This triangle is the most reliable route to the lingual artery (a. lingualis; Pirogov) (see figure). The possibility of accurately determining the course of the lingual artery is the practical significance of Pirogov's triangle.

Pirogov's triangle is part of the medial wall of the submandibular region; to reach it surgically, the patient must be positioned with the head strongly tilted back and turned to the opposite side. By an incision starting at the anterior edge of the sternocleidomastoid muscle at the midpoint of the distance between the lower jaw and the hyoid bone, the skin and subcutaneous tissue with the superficial fascia, the platysma muscle (m. platysma myoides), and the first cervical aponeurosis, which forms the anterolateral wall of the bed (capsule) of the submandibular salivary gland here, are opened; to penetrate deeper, the gland is separated and retracted upward, exposing the thin fascial medial wall of its bed, which is easily separated by blunt dissection, after which a small layer of tissue lining Pirogov's triangle is exposed. Upon removal of the tissue, the intermediate tendon of the digastric muscle, attached here to the lesser horns of the hyoid bone, and both bellies of the muscle are visible, with the posterior belly partially covered by the stylohyoid muscle (m. stylo-hyoideus), which attaches to the greater horn of the hyoid bone. From the greater horn of the hyoid bone, the thin hyoglossus muscle (m. hyo-glossus) runs obliquely upward and inward; along its lateral surface passes the hypoglossal nerve in the form of a white, shiny, round-in-cross-section structure, and below it the lingual vein (v. lingualis). If the hyoglossus muscle is cut transversely or separated bluntly along the course of its fibers just above the hyoid bone, then in the tissue lying behind the muscle, Pirogov's triangle is found and isolated; 1-m. stylo-hyoideus; 2-posterior belly of m. digastricus; 3-m. hyo-glossus; 4-n. hypoglossus; 5-anterior belly of m. digastricus; 6-m. mylo-hyoideus; 7-a. maxillaris ext.; the strongly pulsating lingual artery is found and, if necessary, ligated right there. The described relationships of the artery with the named structures are so precise that its ligation in this place is a relatively easy matter. But cases may arise of either a significant reduction in the size of the already small triangle or even its complete absence, which makes finding the lingual artery very difficult. The base of Pirogov's triangle faces upward toward the hypoglossal nerve, and the apex downward toward the hyoid bone. The dimensions of the triangle are small; its height—the distance from the hypoglossal nerve to the hyoid bone—is on average about one centimeter. Pirogov's triangle is very small in the case when the hypoglossal nerve and the hyoid bone approach each other; then the hypoglossal nerve passes too close to the tendon of the digastric muscle. Pirogov's triangle may be completely absent if the tendon of the named muscle is held at the hyoid bone by a wide and longer-than-usual tendinous loop; as a result of this, the tendon of the digastric muscle rises upward, moves away from the hyoid bone by 3-4 cm, and passes either over the hypoglossal nerve or above it. When approaching the lingual artery in such a case, one has to artificially create Pirogov's triangle by pulling the tendon of the digastric muscle downward.