Diffusion tensor imaging of tract involvement in children with pontine tumors

Abstract

Background and purpose: Conventional MR imaging permits subcategorization of brain stem tumors by location and focality; however, assessment of white matter tract involvement by tumor is limited. Diffusion tensor imaging (DTI) is a promising method for visualizing white matter tract tumor involvement supratentorially. We investigated the ability of DTI to visualize and quantify white matter tract involvement in pontine tumors.

Methods and materials: DTI data (echo-planar, 1.5T) were retrospectively analyzed in 7 patients with pontine tumors (6 diffuse, 1 focal), 4 patient controls, and 5 normal volunteers. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were calculated from the diffusion tensor in 6 regions of interest: bilateral corticospinal tracts, transverse pontine fibers, and medial lemnisci. Relationships between FA and ADC values and results of the neurologic examinations were evaluated.

Results: The corticospinal tracts and transverse pontine fibers were affected more often than the medial lemnisci. The DTI parameters (FA and ADC) were significantly altered in all tracts of patients with pontine tumors (P < .05), compared with those values in the control groups. A marginally significant (P = .057) association was seen between the severity of cranial nerve deficit and decreased FA.

Conclusion: DTI provided superior visualization and quantification of tumor involvement in motor, sensory, and transverse pontine tracts, compared with information provided by conventional MR imaging. Thus, DTI may be a sensitive measure of tract invasion. Further prospective studies are warranted to assess the ability of DTI to delineate tumor focality and improve risk stratification in children with pontine tumors.

Fig 1.

MR imaging and DTI of a 15-year-old patient with diffuse pontine tumor. A, Sagittal T1-weighted image. The pontine tumor is diffusely infiltrative. B, Axial T2-weighted image. The pons appears expanded and hyperintense with an area of focal necrosis. C, Axial ADC map. The tumor demonstrates elevated diffusion, and the necrosis is extremely hyperintense. D, Axial FA map. The tumor demonstrates diminished fractional anisotropy, and necrosis is hypointense.

Fig 2.

Axial diffusion tensor color maps of the brain stem at the level of the middle cerebellar peduncles. A, Image of patient with a pontine tumor showing destruction of the normal anisotropy of the corticospinal tracts and posterior displacement of the medial lemnisci. B, Control image showing normal corticospinal tracts, transverse pontine fibers, and medial lemnisci. C, Image of patient with a pontine tumor showing a diffusely infiltrating pattern.

Fig 3.

Axial diffusion tensor color maps demonstrating tract invasion. A, Image of a 6-year-old patient with a diffusely infiltrating pontine tumor. The left corticospinal tract is enlarged, compared with the right, and tumor infiltration separates the corticospinal (anterior arrow) and corticobulbar (posterior arrow) components. B, Image of an 8-year-old patient with a focally exophytic pontine tumor. Mild lateral expansion of the left corticospinal tract (medial arrow), with focally exophytic tumor (lateral arrow).

Fig 4.

Graphs show diffusion tensor imaging parameters for major white matter tracts in the brain stem. A, Fractional anisotropy (FA). B, Apparent diffusion coefficient (ADC). Data are shown for the corticospinal (CS, blue bars), transverse pontine (TP, red bars), and medial lemnisci (ML, yellow bars). Subject groups included patients with pontine tumors, patient control (PAT), and healthy volunteer (VOL) groups.