Kalyan Natarajan

Skull base growth in childhood

While studying skull base changes in craniosynostosis, it became apparent that there is a lack of reference studies quantifying the changes of three-dimensional (3D) parameters of the normal skull base throughout childhood. Using advanced 3D visualisation techniques, 34 points of the skull base were identified on MRI scans of 66 normal children, aged 1 month to 15 years. Several distances and angles between the various landmarks were measured in an attempt to quantify the growth of skull fossae with age. Two main growth periods were observed: before and after the first 5 years of life. Most change occurred in the first period. Anatomical regional differences were identified between the two sexes. During the first 5 years of life, the anterior fossa showed rapid growth rate with respect to its anterior projection in males, whereas in the females there was a more concentric growth pattern. The body of the sphenoid bone and the middle fossa showed a rapid growth rate in both sexes which was greater in the females. The posterior fossa showed a concentric pattern of growth in both sexes with a greater growth rate in the females. These findings provide new insight into the pattern of growth of the various parts of the skull base and can be used for comparative study of deformities that affect such growth.

Skull Base Growth in Craniosynostosis

Although considerable scientific work has been published on the role of the skull base in craniosynostosis, the changes with age throughout childhood have not been fully outlined. The realisation that little attention has been paid to the posterior skull in craniosynostosis, resulted in renewed interest in skull base growth. The availability of computer-based image analysis provides a new accurate method of study in three dimensions. Using three-dimensional visualisation techniques, 34 points of the skull base were identified on CT scans of 50 children with craniosynostosis of various types, aged from 1 month to 5 years. Several distances and angles between the various landmarks were measured in an attempt to quantify the growth of skull fossae with age. Comparisons were made with normal controls. In children with craniosynostosis, the anterior fossa was overdeveloped in the males, whereas in the females remained underdeveloped throughout the first 2 years of life. The body of the sphenoid showed moderate underdevelopment in the first 2 years in both sexes, the effect being more prominent in the males. The middle fossae showed overdevelopment in both sexes in the first 2 years of life. The posterior fossa was underdeveloped in both sexes in the first 2 years of life, the effect being more prominent in the females. Craniosynostosis seems to affect both sexes to a similar degree, but there are regional differences in the growth pattern. Better understanding of the normal growth pattern of the skull base and the effect of craniosynostosis upon it may assist our approach to surgical treatment and in particular the role of anterior and posterior skull expansive surgery.

The clinical value of electroencephalogram/magnetic resonance imaging co-registration and three-dimensional reconstruction in the surgical treatment of epileptogenic lesions

Abstract With the rapid developments in image processing, new clinical applications of manipulation and three-dimensional (3-D) reconstruction of neuro-imaging are evolving. Combination with other non-invasive techniques aimed at localising electric sources in the brain is of particular interest. These techniques rely on the recording of brain electrical activity and/or the associated magnetic fields from multiple areas on the scalp. Data obtained from an electroencephalogram (EEG) or from magnetoencephalography (MEG) can be fused in 3-D arrangement with anatomical [magnetic resonance imaging/computerised tomography (MRI/CT)] and/or metabolic [positron emission tomography (PET)] data. Such techniques highlight information on the functional correlates of anatomical or space-occupying lesions and their role in the localisation of related symptomatic epilepsy. In the present study we report on methodological issues and preliminary clinical data on spectral EEG/MRI co-registration procedures, offering two examples of children presenting with hemispheric lesions, one frontal tumour and one temporal arterio-venous malformation. The EEG was acquired from 32/64 electrode location. The electrode position and that of four reference points were measured with a dual sensor Polhemus 3D Isotrak digitiser. Sources of EEG activity were determined in 3-D space with the inverse solution method low resolution electromagnetic tomography (LORETA), providing for each frequency component, the topographic distribution of active electrical sources. The positions of the reference points were also measured on MRI, and co-registration of EEG and MRI was achieved using a transformation algorithm. The reconstructed 3-D images of co-registered EEG/MRI clearly demonstrate the relationship between the space-occupying lesion and the epileptic activity. Preliminary results show that in all the patients it was possible to identify with a remarkable accuracy the 3-D topographic relationship between lesion and cortical areas showing localised abnormalities on the EEG. The present method could further enhance the understanding of the effect of resective treatment of structural lesions on brain functioning. The new combined images can be used in combination with image-guided surgery equipment to modify effective surgical resection.

Maxillary volume growth in childhood.

&NA; Nasomaxillary abnormalities in form, position, and development in children are often prominent features of craniosynostosis, and in particular, craniofacial dysostosis. While attempting to quantitatively assess the volumetric maxillary deficiency in these patients, it became apparent that there was no “normal” reference range for maxillary volumes throughout childhood that could be used for comparison. The aim of this study was to generate a model for measuring maxillary volume and subsequent changes throughout childhood. The technique of segmentation was applied to magnetic resonance images obtained in 55 healthy children (30 boys, 25 girls), aged 1 month to 184 months (15.33 years). Maxillary volumes were plotted against age for boys and girls to create a model for normal maxillary growth during the first 15 years of life. Maxillary volumes were larger in boys at all ages. However, the pattern of maxillary growth in boys and girls was similar and could be divided into three periods, each lasting approximately 5 years. During the first 5 years of life, there is a steady increase in maxillary volume, at the end of which the maxilla has reached 53 percent of the volume recorded at 15 years. There is an accelerated rate of growth between 5 and 11 years, which corresponds to the development and eruption of the permanent dentition. Thereafter, until the age of 15 years, the rate of growth of the maxilla plateaus. Maxillary volume in the first 12 months of life is, on average, 29 cm3 in boys and 25 cm3 in girls. By 15 years of age, it has increased to an average of 73.0 cm3 in boys and 59.4 cm3 in girls (an increase by a factor of 2.5 in boys and 2.4 in girls). The difference between the two sexes is statistically significant for the entire series (boys: mean maxillary volume = 56.55 cm3, SD = 24.61; girls: mean maxillary volume = 40.68, SD = 17.69, p = 0.009, one‐way analysis of variance). (Plast. Reconstr. Surg. 111: 1591, 2003.)

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.