The Suprapyramidal Fossa:a3-Dimensional Reconstruction And Surgical Observation

Objective To clarify the position, occurrence rate, and configuration of the suprapyramidal fossa (SF) through surgical observation and3D reconstruction combined with observation of HRCT images of temporal bone to better locate and identify the facial nerve (FN) in surgery of chronic otitis media.Methods The air cell of the SF of300ears with chronic otitis media (COM) was observed during surgery as well as in the corresponding temporal bone HRCT images collected before surgery of these patients in order to define the occurrence rate and location of SF. The air cell and its abutting structures, were reconstructed applying HRCT images in which the SF appeared to define the relationship between the SF and the FN. As a control group, the temporal bone HRCT images of160outpatients who had diagnosed of no ear diseases yet scheduled this test for exclusive diagnosis were collected during the corresponding period to obtained HRCT imaging observational information in these patients.Results In68%(205cases) of patients in the surgical group, the suprapyramidal fossa is present at the posterior wall of the facial recess of the retrotympanum. This air cell usually the only air cell present on the surface of the pyramidal segment of the facial canal, is usually the largest if small air cells are found around it. The position of this air cell is as follows:the pyramidal segment of facial canal medially, posterior part of the tympanic annulus laterally, the incudal fossa as well as aditus and antrum superiorly and the chordal ridge inferiorly. Its configuration varies between round or oval (11.7%,35cases), curved-rod (52.7%,158cases) or irregular (4%,12cases). In control group, the observational rate of the SF was76%(122cases), there is no statistical difference in the occurrence of the SF in these two groups (P>0.05). The sensitivity and specificity of HRCT imaging in detecting the SF were79.0%and88.4%, respectively.Conclusions Occurrence and configuration of the SF is not a rule; however, the positive relationship between the SF and the second genu of the FNC is a rule, if the SF is detected. Considering this, the SF may be a novel anatomic landmark to identify the second genu of the FN during middle ear surgery. However, HRCT imaging has a limited diagnosis value when the SF is atypical.