Neurosurgery notes/Infection/Cranial infection/Parasites/Worms/Echinococcus

Echinococcus

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Worms

General

  • AKA hydatid (cyst) disease

Microbiology

  • E. granulosa
    • General
      • Endemic areas (Uruguay, Australia, New Zealand…).
      • The tapeworms are 2 to 5 mm in length
      • Contain only three to four proglottids (Eggs).
      • Each cyst contains multiple larvae (hydatid sand), and rupture can lead to further cyst formation.
    • Primary definitive host (adult worm)
      • Dog (A dog tapeworm)
    • The intermediate host (larval stage)
      • Sheep
      • Man
    • Life cycle
      • Ova (proglottids) are excreted in dog faeces
      • Contaminate herbage eaten by sheep.
      • Embryos (Oncosphere) hatch and the parasite burrows through the duodenal wall to gain hematogenous access to multiple organs
        • Cysts form in the
          • Liver (65%)
          • Lung (20%)
          • Brain (2%)
      • Dogs eat these infested organs and the parasite enters the intestine where it remains.
      • Man is infected either by
        • Eating food contaminated with ova, or
        • Direct contact with infected dogs.
    • The larva develops into a large cystic lesion
      • Containing
        • External laminar membrane,
        • Germinal layer (the brood capsule),
        • Central fluid layer.
            • Within the cyst fluid are numerous protoscolexes, which form from the brood capsule (refer to figure).
            • Hydatid cyst in lung showing the laminate and proliferative layers. Daughter cysts contain scolices; many of which have degenerated as evidenced by the presence of free hooks. (From the collection of Herman Zaiman, “A Pictorial Presentation of Parasites.”)
            • When ingested by the definitive host, the protoscolexes develop into tapeworms.
            • If the cyst ruptures, however, the protoscolexes can develop into additional hydatid cysts.
            notion image

CNS involvement

  • Occurs in only ≈ 3%.
  • Produces cerebral cysts that are confined to the white matter.
  • Cyst
    • Types
      • Primary cysts
        • Solitary,
      • Secondary cysts
        • Multiple
          • Embolization from cardiac cysts that rupture or from iatrogenic rupture of cerebral cysts
    • Enlarges slowly (rates of ≈ 1cm per year are quoted, but this is variable and may be higher in children),
    • Cyst usually does not present until quite large with findings of
      • Increased ICP
      • Seizures
      • Focal deficit

Evaluation

Bloods

  • Patients often have eosinophilia and may have positive serologic tests for hydatid disease.
  • Enzyme-linked immunosorbent assay (ELISA) or indirect hemagglutination assays are readily available and can be confirmed by immunoblot assays.

Radiological

  • CT
      • Density of the cyst is similar to CSF,
      • It does not enhance (although rim enhancement may occur if there is an inflammatory reaction),
      • Little surrounding edema.
      • It contains germinating parasitic particles called “hydatid sand” containing ≈ 400,000 scoleces/ml.
      CT scan from two patients showing hydatid cysts in brain. Note sharp spherical border with lack of rim enhancement or perifo cal edema. The cyst contents have the same characteristics as CSF.
      CT scan from two patients showing hydatid cysts in brain. Note sharp spherical border with lack of rim enhancement or perifo cal edema. The cyst contents have the same characteristics as CSF.
  • MRI
      • A major cyst with multiple compartments in which smaller cysts
      notion image

Treatment

Medical

  • Albendazole (Zentel®) 400mg PO BID (pediatric dose: 15mg/kg/d) × 28 days, taken with a fatty meal, repeated as necessary.

Surgery

  • Removal of the intact cyst.
  • Every effort must be made to avoid rupturing these cysts during removal, or else the protoscolexes may contaminate the adjacent tissues with possible recurrence of multiple cysts or allergic reaction.
  • The Dowling technique is recommended60:
    • The head is positioned so that the cyst points straight up towards the ceiling when the OR table is 30° head up
    • Drilling burr holes and performing craniotomy must be done very carefully to avoid rupturing the cyst or tearing the dura, which is thin and under tension
    • Do not coagulate with anything but low-power bipolar (to avoid cyst rupture)
    • Open the dura circumferentially away from the dome of the cyst as it may be adherent to the dura
    • Keep the surface of the cyst moist to prevent desiccation and rupture
    • Open the thinned overlying cortex gently, separating it from the cyst with irrigation and cottonoids.
      • The cortical opening need only be ≈ 3/4 the cyst diameter but no less
    • Insert a soft rubber catheter between the cyst and the brain, and gently irrigate with saline as the head of the OR table is slowly lowered 45° while the surgeon supports the adjacent cortex with his/her fingers
    • Continue irrigating more saline and float the cyst out and into a saline filled receptacle
    • If the cyst is ruptured during the procedure,
      • Immediately place a sucker in the cyst to aspirate the contents, remove the capsule, and wash the cavity with saline for 5minutes.
      • Change instruments and gloves.
      • Placing 10% formalin soaked cottonoids on the cavity for a few minutes is controversial61
  • Drapes and potentially contaminated surfaces should be covered with hypertonic saline.