The neuropathology of fatal cerebral malaria in malawian children

Abstract

We examined the brains of 50 Malawian children who satisfied the clinical definition of cerebral malaria (CM) during life; 37 children had sequestration of infected red blood cells (iRBCs) and no other cause of death, and 13 had a nonmalarial cause of death with no cerebral sequestration. For comparison, 18 patients with coma and no parasitemia were included. We subdivided the 37 CM cases into two groups based on the cerebral microvasculature pathology: iRBC sequestration only (CM1) or sequestration with intravascular and perivascular pathology (CM2). We characterized and quantified the axonal and myelin damage, blood-brain barrier (BBB) disruption, and cellular immune responses and correlated these changes with iRBC sequestration and microvascular pathology. Axonal and myelin damage was associated with ring hemorrhages and vascular thrombosis in the cerebral and cerebellar white matter and brainstem of the CM2 cases. Diffuse axonal and myelin damage were present in CM1 and CM2 cases in areas of prominent iRBC sequestration. Disruption of the BBB was associated with ring hemorrhages and vascular thrombosis in CM2 cases and with sequestration in both CM1 and CM2 groups. Monocytes with phagocytosed hemozoin accumulated within microvessels containing iRBCs in CM2 cases but were not present in the adjacent neuropil. These findings are consistent with a link between iRBC sequestration and intravascular and perivascular pathology in fatal pediatric CM, resulting in myelin damage, axonal injury, and breakdown of the BBB.

Figure 1

Brain weights of children in the CM1, CM2, CM3, and COC groups compared with the normal brain weights of age-matched white children. The brain weights of most children in the CM1, CM2, and, to a lesser extent, CM3 groups are higher than the normal values. CI indicates confidence interval.

Figure 2

A and B: Coronal sections through the cerebral hemispheres of a CM2 patient. A: Numerous petechial hemorrhages are distributed throughout the white matter. The lateral and third ventricles are compressed because of edema. B: Close-up view of hemorrhages in the white matter. The gray matter is largely spared. C through G: Vascular changes in CM2 patients. C: The lumen of all small vessels in the field is distended by sequestered iRBCs. D: Some microvascular endothelial cells are hypertrophic and display large vesicular nuclei (arrowheads). E: A small branching vessel in the white matter contains iRBCs and hemozoin. One of the branches (arrow) is occluded by thrombus, is partially denuded of endothelial cells, and is associated with an RH. In the adjacent branch with iRBC sequestration, hypertrophic endothelial cells display large nuclei (arrowhead). F and G: RHs in the cerebral white matter correspond to petechial hemorrhages in A and B. G: Small, often thrombosed, ruptured capillaries containing iRBCs are immediately surrounded by a zone of necrosis that, in turn, is surrounded by a ring of extravasated RBCs, a few white blood cells, and extraerythrocytic pigment granules. C through G: H&E staining. Scale bars: 25 μm (C and D); 50 μm (E and G); 100 μm (F).

Figure 3

Quantification of RHs (A) and RH-associated findings (B–D) in the CM1 (shaded circles) and CM2 (unshaded circles) groups. A: The RHs are present only in the CM2 group and are most numerous in the cerebral white matter, followed by the cerebellar white matter, brainstem, and fiber tracts of the subcortical gray matter. In the cortex, RHs occur at the gray-white matter junction. B: RH-associated myelin damage is confined to the CM2 group and follows the distribution of RHs, being most frequent in the cerebral white matter and gray-white matter junction, followed by the cerebellar white matter and the fiber tracts of the subcortical gray matter and brainstem. C: RH-associated axonal injury occurs only in the CM2 group, follows the distribution of RHs, and is most prevalent in the cerebral and cerebellar white matter and the fiber tracts of the subcortical gray matter, followed by the brainstem. D: Fibrinogen extravasation in association with RHs is confined to CM2 cases, follows the distribution of these hemorrhages, and is most prevalent in the cerebral white matter, followed by the cerebellum, subcortex, and brainstem. hpf indicates high-power field.

Figure 4

Myelin damage in pediatric CM. A: Myelin pallor and fragmentation has occurred in association with an RH surrounding a thrombosed and disrupted parasitized microvessel in the cerebral white matter. B: Irregular, ill-defined, and variably sized foci of diffuse myelin vacuolation and pallor unassociated with RHs typically occur in the CM2 and, to a lesser extent, CM1 groups. C: Areas of diffuse myelin damage encompass several distended microvessels filled with iRBCs (arrows). Luxol fast blue/H&E staining. Scale bars: 50 μm (A); 100 μm (B and C).

Figure 5

Quantification of non–RH-associated damage in the CM1 (shaded circles) and CM2 (unshaded circles) groups. A: Areas of diffuse myelin damage are present predominantly in CM2 and, to a much lesser extent, CM1 patients and are only occasionally found in the nonmalarial groups. B: Diffuse axonal injury is present in both CM2 and CM1 patients, with only occasional small lesions seen in the CM3 and COC groups. The largest areas of axonal damage occur in the cerebral and cerebellar white matter, followed by the subcortex and brainstem. C: Increased permeability to fibrinogen, independent of RHs or thrombosis, is present in the two malaria groups (CM1 and CM2), with no significant differences between the two groups. D: Reactive astrocytes are present in the subcortical and deep white matter of all brain regions examined in both CM1 and CM2 patients. Compared with the CM1 class, the CM2 group exhibits a greater degree of gliosis in the cerebral white matter. hpf indicates high-power field.

Figure 6

Patterns of axonal damage in pediatric CM detected by β-APP IHC. A and B: RH-associated axonal damage. A: Strongly β-APP–immunoreactive swollen and disrupted axons in an RH around a thrombosed and ruptured white matter capillary. B: Only a few β-APP–positive axons are present in the center of some RHs. C through H: Diffuse axonal injury in CM2 patients. Confluent (C) or single (D) ill-defined irregular patches of β-APP–immunoreactive axons in the cerebral and cerebellar white matter (C, E, and F), the gray-white matter junction (D), and pons (G). Diffuse axonal damage occurs in areas with heavy iRBC sequestration (F and G, arrows). H: Smaller diffuse lesions are evident in the medulla. I and J: Small discrete foci of β-APP–positive axons are present immediately adjacent to capillaries occluded by iRBC with (I) or without (J) a thrombus. In sections double stained for β-APP and Luxol fast blue, diffuse axonal and myelin lesions often (K), but not invariably (L), coincide in areas with prominent iRBC sequestration (arrows). Scale bars: 50 μm (A, B, and F–J); 250 μm (C); 100 μm (D, E, K, and L).

Figure 7

Patterns of BBB disruption detected by fibrinogen IHC. A: Fibrinogen extravasation occurs in association with ruptured capillaries and RHs. B: Fibrinogen has extravasated across a microvessel occluded by thrombus. C and D: Increased permeability of the BBB to fibrinogen in microvessels with heavy iRBC sequestration occurs without thrombosis or hemorrhage in the white (C) and gray (D) matter. Scale bar = 50 μm (A–D).

Figure 8

Immunohistochemical demonstration of intravascular monocytes in the CM2 group. Monocytes with phagocytosed extraerythrocytic pigment fill and distend the lumen of many small vessels in the cortex (A), pons (C), and medulla (D). Although adherent to the endothelium (A, inset), monocytes do not transmigrate across the BBB to infiltrate the neuropil. The lumen of several capillaries (A, C, and D) is occluded by adherent monocytes. B: Monocytes, along with pigment and RBCs, have been released from the vascular lumen in an RH. Stainings: CD68 (A and B); CD45 (C and D). Scale bars: 50 μm (A–D); 2 μm (inset).

Figure 9

Reactive gliosis in CM detected by glial fibrillary acidic protein IHC. A: Mild diffuse gliosis in and around an area of myelin pallor and vacuolation and prominent iRBC sequestration. B: Diffuse gliosis in the neuropil around an RH. Scale bar = 100 μm (A and B).