| ObjectiveIn order to orient and avoid damaging important neurovascular structures, from the aspect of operation on the parapharyngeal space (PPS), the anatomic information of the bony structures related to the lateral skull base was obtained. The cadaveric specimens were observed in detail by imitating operations through transcervical approach and transoral-pharyngeal approach.Methods1. The distance and angle among bony landmarks (the root of styloid process, the tip of mastoid process, tympanomastoid fissure, etc) in the lateral skull base in the PPS were determined by measurement of 30 (60 sides) dry adult skulls. So did it to the largest diameter of important foramina.2. The range of the PPS in the cranium bottom district was studied and observed, and its length and width were measured.3. On 10 (20 sides) adult cadaver heads, surgical anatomy were performed by transcervical and transoral-pharyngeal approach. The structures and their relationship in the PPS were carefully observed and recorded, especially in the styloid diaphragm, the last four groups of cranium nerves and the internal carotid artery, etc.Results1. The distance and angle data about styloid process, mastoid process and tympano-mastoid fissure were obtained. It showed that there were remarkable differences in the left side and the right side.2. The measurements of foramina in the lateral skull base showed that there were remarkable differences in the left side and the right side.3. The district of the PPS in cranium bottom was measured. Its length was 33.11±2.95mm (left), 34.88±2.36mm (right), P<0.01. Its width was 17.31±2.22 mm(left),17.15±1.65 mm (right), P>0.05. 4. The shortest distance between mandible and the tip , anterior border of mastoid process and the transverse process of the first cervical vertebra were respectively 22.94±3.08 mm,14. 50±3.57mm,20.34±9.03mm.5. In 20 side samples, there were 30% of the accessory nerves lying in the transverse process of the first cervical vertebra outside, others passing forward. There were 20% of the hypoglossal nerves below the posterior belly of digastrics muscle in 0.5~1.0cm.Conclusion1. The root of styloid process, the tip of mastoid process and the tympanomastoid fissure can be easily detected. The measurement of the distance and angle among reference points can help to orient the important structure, estimate its depth.2. The root of styloid process is a key dissection sign in the PPS. Behind it, there are internal carotid artery, internal jugular vein, cranial nerves, external carotid artery and facial nerve. They must be protected during operation.3. The roof of PPS in the lateral skull base is divided into prestyloid and retrostyloid compartments by the line between the inner margin of lacerated foramen and the root of styloid process. The bony landmarks of prestyloid compartment are medial lamina of pterygoid process, styloid process, great wing of sphenoid bone, petrous pyramid and lacerated foramen. The sign of retrostyloid compartment are jugular foramen and its bone around, the lateral of occipital, occipital condyle. The anterioposterior length of the PPS is from the root of medial pterygoid plate to the lateral-posterior margin of the jugular foramen. The mediolateral width is between the spine of the sphenoid bone and the posterior-medial margin of the jugular foramen.4. The transverse process of the first cervical vertebra can be easily detected on operation, it is an important bony landmarks in which we can look for and protect the accessory nerves. The hypoglossal nerves below the posterior belly of digastrics muscle must be protected on neck dissection.5. The operation space on the PPS is narrow and small; it is very important how to fully expose the PPS. This can be obtained by removing submaxillary salivary gland, the inferior of parotid, styloid process, mastoid process or by abscising digastric muscle, muscle tissue in styloid process, stylomylohyoid ligament, or by subluxating mandible.
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