CLINICAL-SIGNIFICANCE OF ASYMMETRY OF THE FORNIX AND MAMILLARY BODY ON MR IN HIPPOCAMPAL SCLEROSIS

PURPOSE: To investigate the clinical significance of MR-defined asymme try of the fornix and mamillary body for presurgical determination of the side of hippocampal sclerosis in patients with temporal robe epile psy. METHODS: Fast spin-echo MR images were evaluated for evidence of an asymmetrically small fornix and mamillary body in 33 patients with pathologically proved hippocampal sclerosis (presurgical hippocampal s clerosis group), 7 patients who had undergone anterior temporal lobect omy (mean, 3 years from surgery) because of hippocampal sclerosis (pos tsurgical hippocampal sclerosis group), and 34 healthy subjects (contr ol group). Fast spin echo hippocampal volumetry was performed in each patient. RESULTS: In the control group, 6% (2 of 34) of subjects had M R evidence of asymmetrically small fornix and none (0 of 34) of the su bjects had asymmetrically small mamillary body. In the patient populat ion, an asymmetrically small fornix was seen in 42% of presurgical hip pocampal sclerosis group, 39% (13 of 33) ipsilateral, and 3% (1 of 33) contralateral, and in 71% of the postsurgical hippocampal sclerosis g roup (5 of 7), all ipsilateral. In the presurgical hippocampal scleros is group, hippocampal atrophy measured with MR was more severe in pati ents with an ipsilaterally small fornix than in patients without. An a symmetrically small mamillary body was found ipsilaterally in 3% (1 of 33) of the presurgical hippocampal sclerosis group and in 57% (4 of 7 ) of the postsurgical hippocampal sclerosis group; all patients with a n asymmetrically small mamillary body in the postsurgical hippocampal sclerosis group also had an asymmetrically small fornix on the same si de. CONCLUSION: In presurgical hippocampal sclerosis patients, an asym metrically small fornix can be seen ipsilaterally on the side of the h ippocampal sclerosis; however, its low frequency, its association with severe hippocampal atrophy only, and the possibility of false-positiv e results limit its clinical usefulness in determining the side of the seizure focus. An asymmetrically small mamillary body is too rare to be used for presurgical location of hippocampal sclerosis. However, an asymmetrically small fornix and mamillary body are frequently seen on MR images after temporal lobectomy.