242	D.T. Ginat et al.

5.3.12\ Hypothalamic Hamartoma

Thermal Ablation

5.3.12.1\ Discussion

Hypothalamic hamartomas can be difficult to reach and remove via open surgical and endoscopic techniques. Thermal ablation offers a minimally invasive option in cases of associated epilepsy. Notably, it is not necessary to ablate the entire lesion, but it may be sufficient to interrupt the fiber tracks exiting the hamartoma. Therefore, one should not be surprised to find that the ablation zone occupies just a portion of the lesion on postoperative imaging (Fig. 5.55).

Fig. 5.55  Hypothalamic hamartoma laser ablation. Coronal post-contrast T1-weighted MRI shows the peripherally enhancing ablation zone at the neck of the large hypothalamic hamartoma. The patient’s seizures improved after a transient increase in activity shortly after the procedure

5.3.13\ Callosotomy

5.3.13.1\ Discussion

Callosotomy, or surgical division of the corpus callosum, has been used successfully to treat intractable seizures, particularly drop attacks. Division of the corpus callosum can be partial (Fig. 5.56) or total and can be performed via thermal ablation (Fig. 5.57). MRI is the most suitable modality for depicting the extent of the surgical lesioning. The most common postoperative findings include surrounding T2 hyperintensity related to edema in over 20% of cases within 1 week and corpus callosum hematoma in 15% of cases. Other changes following callosotomy include atrophy and signal abnormalities in the cerebral white matter, perhaps related to Wallerian degeneration. The microstructural changes in the transected fibers can persist for many years after surgery and can be detected on diffusion tensor imaging, including fractional anisotropy and apparent diffusion coefficient maps. Therefore, diffusion tensor imaging is useful for depicting which fibers of the corpus callosum remain intact.

5  Imaging the Intraoperative and Postoperative Brain	243
a	b

c

Fig. 5.56  Partial callosotomy. Sagittal T1-weighted (a) and axial FLAIR (b) images show a defect in the body of the body of the corpus callosum (arrow). Diffusion tensor

imaging tractography map (c) shows interruption of corpus callosum body white matter tracts between the genu and splenium of the corpus callosum (arrows)