Neurosurgery notes/Infection/Cranial infection/Parasites/Protozoa/Toxoplasmosis

Toxoplasmosis

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Protozoa

General

  • Serum antibodies are seen in 30% of the normal population.

Microorganism

  • T . Gondii
    • An obligate intracellular organism.
    • The definitive host is the cat.

Pathogenesis

  • Human infection is caused by ingestion of cat feces or raw meat.
  • The cyst may lie dormant until the host becomes immunocompromised.
  • It is the most frequent mass lesion in the brain in patients with AIDS.

Presentation

  • Infection of the mother during pregnancy causes congenital lesions such as
    • Brain necrosis,
    • Periventricular calcification,
    • Hydrocephalus,
    • Hydranencephaly,
    • Chorioretinitis,
    • Hepatosplenomegaly.
  • Acquired infection may cause meningoencephalitis or abscesses.

Evaluation

  • Radiology
    • It is hypoactive on thallium-201 single photon emission CT.
  • Microscopy
    • The cyst is full of and is surrounded by free tachyzoites that can be seen on H & E.
  • Diagnosis
    • Have positive IgG antibiodies to toxoplasmosis on blood testing.

Treatment

  • Non AIDS
    • 4 weeks of sulfadiazine and pyrimethamine with leucovorin (to rescue the cells from the antifolate effects)
  • AIDS
    • Remainder of life
    • Seen in 10% of autopsy cases.
    • Occurs late in the course of HIV infection, usually when CD4 counts are < 200 cells/mm3
    • The most frequent cause of focal neurologic symptoms in AIDS.
    • Present as
      • Mass lesion (toxoplasmosis abscess)
        • The most common lesion-causing mass effect in AIDS patients (70–80% of cerebral mass lesions in AIDS) (see below for CT/MRI findings)
      • Meningoencephalitis
      • Encephalopathy
    • Toxoplasmosis may cause focal or diffuse lesions and predominantly causes basal ganglia and gray/white matter junction lesions.
    • The serum IgG level is increased with infection, and pathologic examination demonstrates a mononuclear inflammation with extracellular tachyzoites and encysted bradyzoites
    • Imaging
      • Most common findings
        • Large area (low density on CT) with mild to moderate edema
        • Ring enhancement with IV contrast in 68% compatible with abscess (of those that did not ring-enhance
        • Many showed hypodense areas with less mass effect, with slight enhancement adjacent to lesion)
        • Well circumscribed margins
      • Most commonly located in basal ganglia, are also often subcortical
      • Often multiple (typically > 5 lesions) and bilateral
      • Usually with little to moderate mass effect (in BG, may compress third ventricle and Sylvian aqueduct, causing obstructive hydrocephalus)
      • Most patients with toxoplasmosis had evidence of cerebral atrophy
    • Treatment: is with pyrimethamine and sulfadiazine for life.