Wallerian Degeneration in the Optic Radiation After Temporal Lobectomy Demonstrated In Vivo with Diffusion Tensor Imaging

Abstract

Summary:Purpose; Diffusion tensor imaging allows the quantitative assessment of the microstructural organization of tracts in vivo (MR tractography). We used the new technique of MR tractography to demonstrate the effects of temporal lobectomy on the optic radiation.Methods: Spatially normalised maps encoding magnitude of the bias (anisotropy) of diffusion of three patients with temporal lobe resections were compared with spatially normalised diffusion maps of 22 control subjects. All three patients were operated on for the treatment of medically intractable temporal lobe epilepsy and had a normal neurologic examination before surgery. One patient had an amygdalocorticectomy. Two patients had standard en bloc resections, one of whom developed a homonymous hemianopia after surgery.Results: In the patient with hemianopia, a significant reduction of diffusion anisotropy (greater than mean ? 2 SD) consistent with wallerian degeneration was demonstrated in the optic radiation on the side of the temporal lobectomy, extending from the temporal to the occipital lobe. In the other patient with standard en bloc resection but clinically no hemianopia, the optic radiation was only marginally affected. In the third patient (amygdalocorticectomy), the diffusion anisotropy was within the normal range in the expected position of the optic radiation.Conclusions; Our findings show that MR tractography may be a useful tool to demonstrate wallerian degeneration in the optic radiation after temporal lobectomy in patients with hemianopia. This is the first time that this new method has been applied in postoperative imaging; it enables us to visualise the morphologic correlate of dysfunctional pathways after epilepsy surgery in vivo. The potential for using MR tractography to study other aspects of epilepsy is discussed. Key Words: MR tractography-Diffusion anisotropy-Intractable temporal lobe epilepsy.Temporal lobectomy is the most common surgical procedure performed for medically refractory symptomatic epilepsy. The optic radiation can be damaged during surgery, resulting in visual field defects. The clinical consequences of temporal lobectomy with regard to visual field defects range from quadrantanopia, which is commonly seen in en bloc resections, to hemianopia, if the resection extends more posteriorly (1). The aim of this study was to investigate the microstructural changes in the optic radiation after temporal lobectomy. We used diffusion tensor imaging (DTI), a new magnetic resonance (MR) technique suitable for the visualization of tracts (MR tractography) (2-4).Accepted January 6, 1999. Address correspondence and reprint requests to Dr. U. Wieshmann at National Society for Epilepsy, MRI Unit, Chalfont St. Peter, Gerrards Cross, Bucks SL9 ORJ, U.K. METHODS SubjectsOne patient with homonymous hemianopia and two patients with clinically full visual fields were selected for this study to compare the optic radiation of patients with and without clinical deficit after surgery. Twenty-two control subjects (14 men and seven women; m...

Changes in fiber tract integrity and visual fields after anterior temporal lobectomy

“…2,3 In particular, Wallerian degeneration may occur when severed fiber tracts are disconnected from their afferent and efferent projections, and there is some evidence that degeneration along temporooccipital fiber tracts correlates with postoperative visual field defects. 2,4,5 Diffusion tensor imaging (DTI) is a quantitative method that can be used to evaluate changes in white matter integrity by measuring the directionality of water along a fiber tract (fractional anisotropy [FA]). 6 We investigate preoperative to postoperative changes in white e-Pub ahead of print on September 29, 2010, at www.neurology.org.…”

“…24,25 Concurrent damage to the pos- terior portion of Meyer's loop can affect the lateral sector, resulting in a complete quadrantanopia, and damage to the superior portion of the optic radiations can cause a hemianopia. 4 This would appear to be the case for TLE01, who sustained a hemianopia and widespread FA reductions along the ILF, splenium of the CC, and adjacent temporo-occipital white matter likely encompassing part of Meyer's loop and the superior optic tracts. Our other patients showed visual defects primarily to the medial sector of the upper quadrant, with more modest involvement of the lateral sector.…”

Longitudinal evaluation of corticospinal tract in patients with resected brainstem cavernous malformations using high-definition fiber tractography and diffusion connectometry analysis: preliminary experience

“…Further decreases in the mean QA values in the most caudal segment (Cases 1 and 3) are potentially consistent with wallerian degeneration occurring over months. 30,34,45 Acute compromise of the fiber tract integrity (e.g., due to hematoma) may be evident using FA within days of the event, 49 with further changes due to wallerian degeneration being observed within months. 30 It is noteworthy that the perilesional decreases in the QA values either deteriorated or stayed stable over the follow-up period and after the removal of the CM and associated hemorrhagic products.…”

Geniculocalcarine Tract Disintegration after Ischemic Stroke: A Diffusion Tensor Imaging Study

“…[20][21][22][23] For example, MR tractography predicts visual field defects following temporal lobe resection. 19 Vision recovery after perinatal stroke as evidenced by functional and diffusion MR imaging has also been shown.…”

“…[16][17][18] Although a case describing vision recovery after a perinatal stroke as evidenced by functional and diffusion MR imaging has been reported, 19 there are no data regarding disintegration of the GCT after an infarction. [20][21][22][23] Understanding ischemic damage to the GCT and probable plasticity is important in determining the prognosis of vision impairment and recovery. We used DTI-derived parameters to measure the GCT in 71 patients with unilateral occipital or temporal-occipital ischemic stroke with GCT involvement.…”