Incidence and clinical relevance of herniation of the mylohyoid muscle with penetration of the sublingual gland.

Swelling of the submandibular region may cause problems in daily clinical diagnosis and requires further exploration. Ultrasonic examination provides a simple, non-invasive and radiation-free method. The goal of our study was to show the high incidence of herniation of the mylohyoid muscle with penetration of the sublingual glands, in some cases clinically imposing as permanent swelling. Penetration was classified into four grades (Grade 0-III). In course of routine examinations of the neck by ultrasound, the anterior part of the mylohyoid muscle was observed in 124 consecutive patients from our outpatient's clinic, presenting with unclear swelling of the neck, mostly due to lymph nodes. In resting position and during swallowing the degree of penetration of the sublingual gland through the mylohyoid muscle was staged. Almost 60% of patients showed an affection of the mylohyoid muscle at either site of varying degrees. In 40% only a thinning of the muscle could be noticed (grade I), whereas in 21 patients (17%) a significant herniation of the gland during swallowing could be observed (grade II). In two patients (2%) a constant breach of the mylohyoid muscle with permanent herniation of the gland imposing as swelling could be seen (grade III). Occasional or permanent penetration of the sublingual gland through the mylohyoid muscle is not a rare finding and can be found in almost every fifth individual using ultrasound. This may impose clinically as permanent swelling and may be of value in the differential diagnosis of swelling in the submandibular region.