A neonate was noted to be microcephalic and hypotonic. Clinical examination showed evidence of bilateral chorioretinitis. Following a seizure, a CT scan was obtained.
CT is more sensitive to calcification than MR and helps suggest the diagnosis.
MR is more sensitive than CT to the absence of cortical dysplasia, which assists in differentiation from CMV.
Pitfalls
Intracranial calcifications may regress or even resolve over time in cases of treated toxoplasmosis. This correlates with the intensity of antimicrobial therapy and is accompanied by neurologic improvement.
Radiologic Findings
An axial non-contrast CT (Fig. A ) shows prominence of the lateral ventricles and third ventricle out of proportion to the sulci, consistent with hydrocephalus. In addition, multiple irregular calcifications are present within the basal ganglia bilaterally and also scattered throughout the brain parenchyma. A more cephalad image (Fig. B ) shows bifrontal extra-axial collections consistent with subdural hygromas or chronic hematomas. Areas of cystic encephalomalacia are present, and mutlifocal irregular parenchymal calcifications are again identified.
Diagnosis
Congenital toxoplasmosis
Differential Diagnosis
Congenital cytomegalovirus (periventricular Ca2+, often polymicrogyria)
Congenital rubella (severe microcephaly, more subtle pattern of Ca2+)
Discussion
Background
Congenital toxoplasmosis develops after the parasite Toxoplasma gondii is passed to the fetus transplacentally. This usually occurs when an immunocompetent mother is infected for the first time during gestation, but congenital transmission may also occur from a mother who is immunocompromised and chronically infected. Congenital toxoplasmosis is second in frequency to cytomegalovirus infection among the TORCH infections. The incidence of congenital toxoplasmosis is about 1 to 2 cases per 1000 births per year.
Etiology
Toxoplasmosis is caused by the obligate intracellular protozoan parasite Toxoplasma gondii. This usually infects human beings via inadequately cooked meat that harbors oocysts (cattle, sheep, and pigs are intermediate hosts), but may also be acquired from contact with cats (the definitive hosts) and from unwashed fruits and vegetables via a fecal-oral route. CSF adds pleocytosis and elevated protein.
Clinical Findings
Most infants are asymptomatic at birth, with onset of symptoms in the first days to weeks of postnatal life. Infection may be generalized or concentrated primarily in the CNS. CNS findings include chorioretinitis (bilateral in 85%), hydrocephalus, and seizures. Severely affected patients have microcephaly, tetraplegia, mental retardation, and/or blindness.
Pathology
Gross
Ventricular dilatation, scattered calcifications
Microscopic
Multifocal necrotizing granulomatous infection that is often accompanied by a granular ependymitis
Imaging Findings
Both CT and MR may show ventricular dilatation and areas of encephalomalacia
CT
Scattered multifocal cerebral calcifications with less of a periventricular predilection than CMV
MR
Delayed myelination
Focal areas of parenchymal destruction
Treatment
Usually long-term treatment with the antimicrobials pyrimethamine and sulfadiazine
If infection is diagnosed in utero, maternal treatment with spiramycin can reduce the incidence and severity of congenital infection
Prognosis
Variable, depending on early identification and prompt institution of therapy. This has been greatly aided by neonatal screening programs. In children treated for 1 year, signs of active CNS infection (CSF pleocytosis, elevated CSF protein) resolved, and this group had significantly better neurologic and developmental outcomes than a group that was untreated or treated for less than 1 month.
Selected Readings
Becker LE. Infections of the developing brain. AJNR 13:537-549, 1992.
Patel DV, Holfels EM, Vogel NP, et al. Resolution of intracranial calcifications in infants with treated congenital toxoplasmosis. Radiology 199:433-440, 1996.
Roizen N, Swisher CN, Stein NA, et al. Neurologic and developmental outcome in treated congenital toxoplasmosis. Pediatrics 95:11-20, 1995.
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