Several anatomical textbooks and atlases describe the morphology of the parotid gland as a wedge-shaped serous gland with an anterior-posterior length of 35 ± 5.7 mm15 although many variations have been observed in the appearance, extent, shape, and tail of the gland during actual dissections. Recent literature and anatomy textbooks have not paid much attention to the detailed anatomy of the parotid gland and tail. In 1977, Park et al.16 classified the parotid gland into four types according to its morphology: inverted triangular shape (66.7%), oval shape (15.5%), inverted L shape (8.9%), and roughly triangular shape (8.9%). The parotid tail is the most inferior portion of the superficial lobe. It is triangularly shaped and is located deep to the platysma muscle, anterolateral to the sternocleidomastoid muscle, and posterolateral to the posterior belly of the digastric muscle17. In our study, type I, the pistol-shaped parotid gland, was observed in 63.3% of cases and type II, the oval-shape parotid gland, was observed in 36.7% of the cases. We found that the percentage and shape of the inverted triangular shape described by Park et al. are similar to those of the pistol-shaped parotid gland (type I) in our study (Fig. 1).
The description of the boundaries of the superficial lobe of the parotid gland is also different in each textbook. According to the measurements in this study, the parotid gland is located in the anterior aspect of the mandibular ramus and covers the posterior part of the masseter muscle below the zygomatic arch from the otobasion inferius. The superior border of the parotid gland was located 13.4 ± 4.1 mm below HL. Due to the large distance of the parotid gland from HL to the inferior border of the zygomatic arch (11.0 ± 2.3 mm), if a clinician injects botulinum toxin into the lower part of the face to contour the face to be slimmer, most of the toxin may be injected into the parotid gland.
Below the otobasion inferius (between P2 and P3), the parotid gland was located at the posterior part of the ramus and angle of the mandible. Below the angle of the mandible, the parotid gland tail extended 13.2 ± 4.2 mm inferiorly and vertically to ML. The posterior aspect of the parotid gland, measured horizontally from P4 to ML was 31.5 ± 6.3 mm. This result indicated that the parotid gland tail continued to extend below the mandible and covered the anterior border of the sternocleidomastoid muscle (Fig. 3). For this reason, clinicians should be careful during thread-lifting procedures in the neck region. It is worth noting that the most anteriorly projected portion of the parotid gland extended in the direction in which the parotid duct ran.
In our study, the depth from the skin to the parotid gland surface was measured using a 3D scanner. A 3D scanning system is commonly used to estimate clinical outcomes in both invasive and non-invasive procedures involving the head and neck area. Morphological research using the 3D scanning system could provide in-depth data about the anatomical structures of the face, providing us crucial anatomical knowledge that can be used in a variety of clinical applications. The registration technique has been used to accurately determine the depth from the skin to the muscle in our previous cadaveric studies18–21.
Understanding the anatomy of the parotid gland is important and helpful when injecting mid and lower-face fillers, injecting botulinum toxin, and performing thread lifting procedures. The cadaver can be placed on the operating chair to recreate the posture that patients undergoing a procedure are positioned in. This can allow for an accurate assessment of the effect of posture during surgery on the anatomy of the parotid gland. The deformation of facial soft tissues due to change in the anatomical position is often overlooked and only a limited number of studies were conducted on this subject22–24. The facial soft tissues in the midsagittal landmarks were found to be more stable and less varied than those in the lateral aspect of the face. The displacement of the facial soft tissues due to the anatomical posture was larger toward the lateral side of the face, which includes the parotid gland. 23. It is necessary to be aware of this displacement of soft tissues with the change in the anatomical position to avoid damage to the parotid gland during invasive or non-invasive procedures involving the head and neck.
The limitation of our study, we only dissected cadavers of older individuals. In an earlier study, no statistically significant difference in the size of the parotid gland was found between older and younger individuals15. To explore this further, newer studies may be necessary to assess the morphology and the displacement of the parotid gland due to body posture in younger individuals.
In conclusion, in this study we identified the location of the parotid gland and parotid tail through cadaveric dissections, thus providing topographic information that can be used as a reference for invasive and non-invasive procedures in the parotid gland region. Earlier studies have demonstrated that displacement of facial soft tissues occurs with a change in body posture. In light of this information, the results of this study can serve as a reference to surgeons when performing minimally invasive procedures in the head and neck region to avoid surgical complications.