THE LATERAL PROJECTION IN TOMOGRAPHY OF THE PETROUS PYRAMID

¹ From the Department of Radiology, Columbia University, College of Physicians and Surgeons, New York, New York

Because of their anatomic orientation in the petrous pyramid, the external auditory canal, the vertical portion of the facial canal, the malleus and the incus and the round window can best be seen on the lateral tomogram.

Clinical examples have been shown of the value of the lateral tomogram in revealing the pathologic processes affecting these structures.

The "molar tooth sign" is of diagnostic significance; i.e.,, the normal outline of the malleus and incus in the lateral tomographic projection resembles a molar tooth with the crown of the tooth formed by the head of the malleus and the body of the incus, the anterior root by the handle of the malleus, and the posterior root by the long process of the incus. Any irregularity in this molar tooth outline indicates a pathologic condition affecting the malleus and incus or both. The locus of the pathology would be indicated by the portion of the molar tooth outline which is abnormal or displaced.

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