PROPELLER MRI visualizes detailed pathology of hippocampal sclerosis

Abstract

Purpose: Hippocampal sclerosis (HS) is the most common cause of refractory temporal lobe epilepsy. Histopathologically, HS is characterized by neuron loss and gliosis. HS can be identified on MRI by signal increase on T(2)-weighted images and volume loss on T(1)-weighted volume images. The Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction ("PROPELLER") sequence has excellent contrast between grey and white matter and compensates for subjects moving during the scan. The aim of the current report was to explore PROPELLER image quality of the hippocampus compared to routine sequences.

Methods: Routine sequences (T(1) volume, T(2)-weighted, PD and FLAIR images) and PROPELLER images were acquired in four presurgical patients with HS using a GE 3T Excite HD scanner (General Electric). Resected tissue was stained with LFB, and for GFAP, NeuN and dynorphin immunohistochemistry. Hippocampal sections were compared with PROPELLER images.

Results: PROPELLER images were T(2)-weighted and had superior tissue contrast compared to routine sequences. PROPELLER images showed the internal hippocampal structures and tissue changes associated with HS. This corresponded to changes seen on histopathological sections confirming that the sequence could distinguish between different strata and subfields of the hippocampus.

Discussion: The PROPELLER sequence shows promise for detailed in vivo imaging of the hippocampus in patients who did not move overtly, negating the inevitable subtle movements during scans. More detailed in vivo studies of the hippocampal formation, investigating subtle abnormalities such as end folium sclerosis, and the neocortex are now possible and may increase the diagnostic yield of MRI.

Figure 1

T₁-weighted volume (left column), T₂-weighted (middle) and PROPELLER (right) MRI scans at equivalent planes through the hippocampus from three patients. The PROPELLER scans had superior contrast between grey and white matter and within the hippocampal formation. HS can be seen in all patients (left HS, i.e., right on MR images, top and bottom rows; right HS, i.e., left on MR images, middle row). Arrowheads indicate the normal band of myelinated tissue in the superficial aspect of the parahippocampal gyrus extending into the hippocampus proper. Arrows indicate the normal grey matter signal of the subiculum, CA1 and the “C”-shaped contours of the dentate gyrus with intervening white matter strata (strata moleculare, lacunosum and radiatum).

Figure 2

Zoomed PROPELLER image of right (a) and left (b) temporal lobe in patient 1 with left HS. The left temporal lobe has been magnified (c) for comparison with corresponding histopathological sections. Subiculum appears normal on both PROPELLER images and histopathological sections (d; LFB, e; GFAP and f; NeuN immunohistochemistry). There is an abrupt transition to atrophy and signal increase in CA1 (red arrow). This signal increase and atrophy involved all hippocampal subfields, including the hilus. Gliosis (seen best with GFAP) and neuronal loss (seen best with NeuN) were confirmed in these regions on histopathological sections. Mossy fiber sprouting was confirmed on dynorphin immunohistochemistry (g). This was not appreciable in PROPELLER images.

Figure 3

Zoomed PROPELLER images of right (a) and left (c) temporal lobe in patient 2 with right HS. The right temporal lobe has been magnified (b) for the comparison with matched histopathological sections (d, e). NeuN immunhistochemistry confirmed neuronal loss and atrophy (d). The myelinated tissue in the intervening white matter strata (strata moleculare, lacunosum, and radiatum) is clearly seen on the LFB-stained section (e, red arrow) and is indicated by a red arrowhead in the unaffected, normal hippocampus (c). It is less conspicuous on the sclerotic side in this case (b, red arrow). The black arrow and arrowhead indicate the hilus on the sclerotic and normal side respectively.

Figure 4

Zoomed PROPELLER image of right (a) and left (b) temporal lobe in patient 3 with left HS. The left temporal lobe has been magnified (c) for comparison with corresponding histopathological sections (d, e). Only a small amount of hippocampal subfields CA1-3 were available in the histopathological sections. The myelinated tissue in the strata moleculare, lacunosum, and radiatum is clearly seen on the LFB-stained section (e) and can also be appreciated on the section immunolabeled for NeuN (d). Arrows indicate the corresponding areas on the PROPELLER image of the sclerotic hippocampus (c) and histopathological sections (d, e).

Figure 5

Zoomed PROPELLER image of the left temporal lobe (a) with corresponding histopathological sections for patient 4. All hippocampal subfields are available in the histopathological sections. The myelinated tissue in the strata moleculare, lacunosum, and radiatum is clearly seen on the LFB stained section (b, red arrow indicates the corresponding area of low signal on the PROPELLER images). Sections immunolabeled for GFAP (c) show the abrupt transition to gliosis in CA1 (black arrow). This corresponds to signal increase on PROPELLER images (white arrow). The neuronal loss can be seen on sections immunolabeled for NeuN (d, black arrow) with good preservation of nerve cells in subiculum and some nerve cells also preserved in CA3. Section immunolabeled for dynorphin shows mossy fiber sprouting (e).