Incidence and Prevalence
- Greater than 60% at presentation: For patients with cerebellar and fourth ventricle tumors, hydrocephalus is present at diagnosis in more than 60% (17), up to 82–91% (5, 6, 21).
- Less than half need permanent treatment: After tumor removal, treatment of hydrocephalus is required in only 15.5–36% (5, 7, 23, 31).
- Under 3 years of age: Cully et al. found that patients younger than 3 years at the time of tumor diagnosis had an increased incidence of hydrocephalus that required treatment (7).
- None recognized: There is no specific sex predilection for this type of hydrocephalus. It could be said that it follows the sex predilection of the specific tumor type (e.g., males for medulloblastomas).
- None found
Many authors have tried to identify possible factors that could help determine which patients will require long-term treatment of hydrocephalus after removal of a posterior fossa tumor.
Degree of preoperative hydrocephalus
- Ventricular index not predictive: The ventricular index [has been used as a tool in the assessment of the degree of preoperative obstructive hydrocephalus secondary to a posterior fossa tumor, but there is no agreement among authors about its validity as a significant factor for predicting the need for shunt placement (25).
- Degree of hydrocephalus controversial: Schmid and Seller (37) did not find symptoms of raised ICP or the degree of ventricular enlargement to be predictive of hydrocephalus needing treatment, while Dias and Albright (9) supported the notion that the severity of preoperative hydrocephalus in patients with posterior fossa tumor was predictive.
- Image analysis of ventricles: A recent study demonstrated that the degree of preoperative hydrocephalus as determined by image analysis of CSF appears to have a statistically significant predictive value for the need for shunting in children after removal of their posterior fossa medulloblastomas (22).
Location of tumor
- Midline tumors: Culley et al. found that tumors affecting midline structures were more likely to be associated with hydrocephalus that required treatment (7).
Histology of tumor
- Medulloblastomas most likely: Due-Tønnessen and Helseth reported that the need for early CSF diversion (ventriculoperitoneal shunt or ETV) after posterior fossa tumor surgery in children was highly dependent on tumor histology, with the highest rate 53% of patients with medulloblastomas and the lowest rate 17% of patients with astrocytomas (10).
Extent of tumor resection
- Subtotal resections: Culley et al. described patients who had subtotal resections as being more likely to need shunting for their hydrocephalus (7).
Need for management of hydrocephalus perioperatively
- Prolonged dependency on EVD: Culley et al. noted that patients requiring EVD for prolonged periods usually needed permanent treatment for their hydrocephalus (7).