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Imaging Diagnosis

The MR findings in cerebral malaria show similar cerebrovascular lesions. Acute hemorrhage and infarction have been shown 5 days after the onset of neurological symptoms. In one patient, 1.5-T scans with T1- and T2-weighted images showed increased signal intensity compatible with hemorrhage, and hyperintense areas suggesting infarctions. Follow-up scans 24 days later, after intravenous quinine, showed a decrease in the size of the lesions and the patient's clinical condition had also improved. In another patient, MR scans showed severe diffuse encephalopathy and a focal pontine lesion, consistent with the neurological clinical signs. Cerebral scanning can therefore provide information when patients with cerebral malaria exhibit focal neurological signs. The cerebral edema may be sufficiently severe in infants and young children to cause suture diastasis, which can be recognized on skull radiographs. For the majority of patients with cerebral malaria, imaging will not alter the immediate therapy: CT or MR scans may be of more importance when neurological recovery is incomplete. The imaging findings are nonspecific and noncontributory. Unless a concomitant infarct or infection is suspected, there is usually no reason to image the brain during cerebral malaria.

The kidneys may become small and contracted in chronic malaria but the imaging findings are nonspecific. In blackwater fever the kidneys enlarge and there is renal failure.

The lungs usually remain normal radiologically during acute malaria, although clinical bronchitis occurs in children and responds to antimalarial therapy. Pneumonia and bronchopneumonia may also occur, particularly in the malnourished. As already noted, it has been suggested that children in West Africa who have markedly high parasitemia may have abnormal chest radiographs. The changes reported were a generalized increase in interstitial markings (of unspecified origin). The interpretation of interstitial markings on the chest radiographs of small children can be very controversial and this report, based on one series, needs confirmation. So many small children worldwide are affected by malaria that it is surprising there are no similar reports. In some adults with either falciparum or vivax malaria, the chest radiographs may show pleural effusions, sometimes bilaterally. The lungs may show hazy areas of diffuse interstitial and/or alveolar edema: these are nonsegmental, although occasionally they may coalesce until there is lobar consolidation. The most common interpretation is likely to be of viral or bacterial pneumonia, but there is no clinical evidence to confirm this, and there is no response to antibiotic therapy. However, the lungs do clear with treatment for malaria; the radiographs should return to normal in 3 to 7 days, with a minority taking a few days longer.

The severe pulmonary edema, which is usually fatal, has no unusual radiological characteristics (Fig. 46.2). There is no cardiac enlargement and no evidence of heart failure: small pleural effusions have been reported. Pulmonary edema can occur acutely and unexpectedly, even when the patient has been on treatment for malaria for a few days. Early recognition offers the only possibility of reversal. Unfortunately, even strenuous therapy may not be successful.
Bowel involvement, even infarction, may lead to gastrointestinal symptoms; gastroenteritis is a common complication of malaria but has no specific radiological findings. It can be due to prophylactic drugs.

In summary, the most important factor in diagnosing malaria is to be aware of that possibility, and the most useful contribution to be made by a radiologist is to remember that pulmonary changes and pleural effusions may be due to malaria, particularly the severe pulmonary edema which has such a poor prognosis.

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Copyright: Palmer and Reeder