Computer simulation of a neurosurgical operation: craniotomy for hypothalamic hamartoma

Although magnetic resonance imaging has revolutionised the management of intracranial lesions with improved visualisation of anatomical structures, it only produces two-dimensional images, from which the clinician has to extrapolate a three-dimensional interpretation. Several approaches can be used to create 3D images; the discipline of image segmentation has encompassed a number of these techniques. Such techniques allow the clinician to delineate areas of interest. The resulting computer-generated outlines can be reconstructed in a three-dimensional arrangement. Although a plethora of "generic" segmentation techniques exist, we have developed a refined form, dependent on general and particular properties of the anatomical structures under investigation. High-contrast structures such as the ventricles and external surface of the head are found by using a localised adaptive thresholding technique. Less definable structures, with poor or nonexistent signal change across neighbouring structures, such as brain stem or pituitary, are found by applying an "energy minimisation"-based technique. To demonstrate the techniques we used the example of an 8-year-old boy with uncontrolled gelastic seizures due to a hypothalamic hamartoma, who is being considered for surgery. We were able to demonstrate the anatomical relationships between the hypothalamic hamartoma and adjacent structures such as optic chiasm, brain stem and ventricular system. We were subsequently able to create a video, reproducing the stages of craniotomy for excision of this tumour. By creating true 3D objects, we were able at any stage of the simulation to visualise structures situated contralaterally to the approaching surgical dissector. These 3D representations of the structures can be either invisible or opaque, in order to afford 3D localisation as the "virtual" surgical dissection proceeds. The clinical application of such techniques will enable surgeons to improve their understanding of anatomical relations of intracranial lesions and has obvious implications in image-guided surgery.