The anatomic basis for ultrasound in the diagnosis and treatment of styloid process–related diseases

BACKGROUND: The styloid process (SP), stylohyoid ligament and lesser horn of hyoid bone together form the stylohyoid chain. Differences in the ossification degree and the connection sites of each segment of the stylohyoid chain on both sides lead to variations in the length, orientation, thickness, and straightness of SP. The incidence of elongation of the SP, known as styloid process syndrome (SPS), is around 4%, with only 4% of patients showing elongation show symptoms. Computed tomography (CT) remains the first-choice auxiliary examination for diagnosing SPS, but its performance can be affected by a variety of factors. Ultrasound can reveal the parapharyngeal space and adjacent structures, which offer high consistency with CT findings. Here, we investigated the ultrasonographic features of the SP and its adjacent structures in normal adults and assessed the clinical utility of ultrasound assessment for SP-related diseases. METHODS: With the ramus of mandible, mastoid process, SP, and salivary gland as the anatomical landmarks, ultrasonography was conducted on the parapharyngeal space in 78 healthy adults. The scans were performed along the oblique coronal section of the ramus and the cross-sectional plane between the mastoid process and ramus to visualize the SP and its adjacent structures. The SP length, the shortest distance from the SP tip to the outer edge of tonsil (SP-tonsil distance), and the distance from SP to the internal carotid artery (SP–ICA distance) were measured. RESULTS: SP and its adjacent structures were successfully visualized on ultrasonography in all 78 subjects. The measured SP length was 2.65±0.48 cm. The SP–tonsil distance was 1.95±0.50 cm. The SP–ICA distance was 0.509±0.231 cm. The SP length and SP–tonsil distance measured by ultrasound were not significantly different from those measured by CT (P=0.071, P=0.053). Furthermore, the SP length and SP–tonsil distance measured by ultrasound were positively correlated with CT measurements (r=0.917, P=0.071; r=0.978, P=0.053, respectively). SP–tonsil distance was negatively correlated with SP length and SP inward deflection angle. CONCLUSIONS: Ultrasound can accurately reveal the shape and size of SP and its adjacent structures and thus will be helpful for the diagnosis of SP-related diseases.