Displaced corticospinal fibre tracts by a pontine cavernoma

A 53-year-old man with a left pontine cavernoma presented with sudden onset headache and left facial paraesthesia. Examination showed decreased sensation to light touch in the ophthalmic and maxillary divisions of the trigeminal nerve with absent motor signs. Magnetic resonance imaging showed an acute bleed into a pontine lesion measuring 2.0 ¥ 1.7 cm (Fig. 1a). Diffusion tensor imaging (DTI) tractography (Fig. 1b) demonstrated displacement of the left corticospinal tract (arrows), more medial than normal (rectangles in Fig. 1a,b). There was no interruption of the corticospinal tract (star in Fig. 1b) accounting for the lack of motor dysfunction. The cavernoma was successfully removed with resolution of the facial sensory disturbance 48 hours post surgery. Surgical excision of deeply situated lesions can injure white matter tracts and cause subsequent disability. DTI tractography provides non-invasive, in vivo visualization of the orientation and integrity of white matter tracts. DTI tractography utilizes the principle that water diffuses along the fibre tracts. The direction of the maximum water diffusion is traced and using various algorithms, the location and course of white matter tracts can be visualized in relation to any structural lesion. Pre-operatively, DTI tractography can be use to plan lesion resection to avoid injury to eloquent white matter structures. In this case, DTI tractography was able to illustrate the displacement of normal fibre tract anatomy by a cavernoma, correlate the man’s non-disabling clinical features with his pathology and assist in the successful resection of the cavernoma with no postoperative morbidity. Received 2 April 2009; accepted 5 April 2009.