Dr. Mitusha Verma

Dr. Mitusha Verma
Consultant Radiologist
MRI Department of
Nanavati Super Speciality
Hospital, Mumbai

Lighting the Path

Tracing the tracts with Diffusion Tensor Imaging

Imaging has grown much beyond its morphologic aspect to providing functional and physiologic details. With current non-invasive MRI techniques, one may assess the Tumour grade, suggest the best possible surgical approach, prognosticate as well as perform post treatment follow-ups to see for treatment response, residue and possible recurrence.

Where on one hand non-contrast sequences like Arterial Spin Labelling used to assess tumour blood flow have the advantage of being non-invasive, sensitive, cost effective and repeatable, sequences like Diffusion Tensor Imaging provide further insight to Tumour characteristic and help in pre-operative planning.

Diffusion Tensor Imaging (DTI) provides superior visualisation and quantification of Tumour involvement in relation to various white matter tracts. It can delineate tract invasion and displacement. These not only helps to discriminate between diffuse and focal brain stem Tumours, grade these masses but also to guide the best path to be followed during surgical biopsies and excisions. It has been quite well established in supratentorial masses but with the present state-of-the-art imaging techniques, we can achieve considerable level of sensitivity for brain stem lesions as well.

This was well-projected with a recently performed MRI on a two year old girl who was experiencing imbalance while walking, making her prone to frequent falls. A 3.9 x 3.7 x 3.1 cm sized, heterogenous mixed signal intensity, predominantly T2 hyper-intense, well-defined lesion was detected with its epicentre in her right half of pons and an exophytic component extending into the right cerebella-pontine angle cistern. The lesion was hypo-refused on Arterial Spin Labelling as well as DSC perfusion.

Diffusion Tensor Imaging clearly depicted the relation of this pontine mass lesion with the adjoining white matter tracts. The mass was seen displacing these tracts changing their colour hues rather than destroying them. The corticospinal tracts, was seen displaced along its right lateral margin, whereas the right middle cerebellar peduncle and central tegmental tract were seen effaced along its right lateral margin. No major white matter tract was identified along the posterior aspect of the lesion, thereby making this approach suitable for surgery. On histopathology this pontine mass turned out to be WHO Grade I, localised pontine pilocytic astrocytoma.

Given the present advanced imaging techniques, Tumour imaging protocols must include advanced sequences like Arterial Spin Labelling, DSC perfusion, 3D BRAVO, Neuronavigation, MR spectros-copy as well as Diffusion Tensor Imaging to provide all possible morphologic as well as functional details, besides routine morphologic sequences like T1WI, T2WI, DWI, SWAN and FLAIR.