For the purpose of a clear demonstration of the skull base structures by computed tomography (CT), we first investigated a model human skull (embedded into 2% agar gel containing 0.1% iodine) by examining it with EMI-CT1010 with the scanning plane at +25° to -90° to Reid's base line. The overlapping slice and magnification method was used at the same time for examining the optic canal, sella turcica and internal auditory meatus.
In the model study the optic canal was best viewed with the scanning plane at -10° to Reid's base line, the sella turcica and the anterior part of the posterior fossa were at -20°, the anterior half of the middle fossa was at -30°, the anterior skull base and the internal auditory meatus were at -40°.
Clinically, 10 cases (sphenoidal ridge meningioma, craniopharyngioma, recurrence of sphenoidal ridge meningioma, hematoma in the cerebellum, cerebellar astrocytoma, orbital tumor, pituitary adenoma, recurrence of tuberculum sellae meningioma, acoustic neurinoma and C-P angle meningioma) were examined by CT with the scanning plane at +25° to Reid's base line (ordinary section) and the plane at -10° to -40° (reverse section) used in the model study.
With reverse sections, the size and extent of lesions and their relationship to the base of the skull were delineated better than in those with ordinary sections. The two-plane CT examinations (ordinary section and reverse section) were helpful for three-dimensional evaluation of lesions and in determining the best method for surgery or radiotherapy.
From a technical point of view, it is emphasized that a reverse section can be done by head scanners with no difficulty in patient positioning. Reverse section produces an insignificant amount of artifacts caused by body movement, air in the paranasal sinuses and tooth fillings.