Relevance of sinonasal anatomical variations in the preoperative evaluation by computed tomography for endonasal surgery

Endonasal surgery is utilized in diagnosis, biopsy, management and follow-up of several sinonasal diseases. In order to perform this procedure with the appropriate safety, preventing iatrogenic lesions, it is essential that the surgeon can preoperatively rely on an appropriate mapping of bone structures involving the nasal fossae, paranasal cavities and their drainage pathways. The imaging method of choice for this evaluation is computed tomography (CT), considered as the golden-standard, based on the evaluation of axial, coronal and sagittal images. Coronal images can be directly acquired, preferentially with the patient in ventral decubitus, or otherwise being reconstructed from axial images. Spiral, and especially multislice CT equipment allow multiplanar image reconstruction with a quality similar to the images directly acquired in the coronal plane, with the advantage of eliminating artifacts originated by eventual dental restorations. Sagittal reconstructions supplement the anatomical detailing of paranasal cavities provided by coronal images, especially of frontal sinuses and frontal recess. Anatomical variations involving the ethmoid sinuses are very frequently found. Earwaker, evaluating 800 patients, has observed 52 types of variations involving the nasal fossae and paranasal cavities, with 93% of patients presenting one or more of these variations. Some of the variations have no clinical significance; however, other should be valorized and described, considering that they may be related to the genesis of sinusopathy or even may affect endonasal