Sellar susceptibility artifacts: theory and implications.

PURPOSE To investigate the prevalence and physical basis of a specific form of MR susceptibility artifact that may be seen in the pituitary gland near the junction of sellar floor and sphenoidal septum. MATERIALS AND METHODS Coronal, T1-weighted MR images of the pituitary glands in 50 subjects without clinical evidence of pituitary or sphenoidal sinus disease were reviewed to determine the prevalence of a focal susceptibility artifact near the sellar floor. A plexiglass phantom was constructed to duplicate this artifact in vitro, the appearance of which was studied by varying the direction and intensity of the readout gradient. RESULTS In the clinical studies, a focal artifact larger than 1 mm2 was observed in MR studies of seven (14%) of 50 subjects and was sufficiently large to mask or mimic pathology in all cases. The location of this artifact was always within the pituitary gland but closely related to the junction of the sphenoidal septum and sellar floor. The artifact was successfully reproduced in the phantom, and its magnitude was shown to be linearly related to the strength and direction of the readout gradient. An explanation for the focal nature and shape of this artifact is presented based on consideration of the boundary conditions of the Maxwell equations of electromagnetism. CONCLUSION A focal susceptibility artifact may be seen on MR images of the pituitary gland closely related to the junction between the sellar floor and sphenoidal septum that may mimic or obscure a microadenoma.