A magnetic resonance imaging (MRI) of her brain was performed urgently; the scan is shown in Fig. 61.1.

• This child demonstrates typical findings for slowly progressive intracranial pressure in this age group.
  
• The reasons for this could be hydrocephalus, with mass lesion as a cause.
  
• Posterior fossa masses are common in this age group.
  
• Arachnoid cysts occur, postinfectious or hemorrhagic hydrocephalus also occurs, and in some children subdural hematomas present in this fashion (even as a result of nonaccidental trauma).1
  
• Benign macrocrania with benign enlargement of the subarachnoid spaces should not present with this constellation of developmental delay and neurologic exam findings.

• This child needs urgent imaging.
  
• Ultrasound, computed tomography (CT) scan, or MRI scan are all reasonable options depending on the availability, though MRI is clearly the most definitive, and might be required regardless of the result of the other studies.

• The MRI shows a cerebrospinal fluid (CSF) density collection in the region of the suprasellar cistern and 3rd ventricle with associated obstructive hydrocephalus.
  
• Typically, arachnoid cysts of the suprasellar space may extend up and compress the 3rd ventricle and obstruct the foramen of Monro causing hydrocephalus.
  
• Arachnoid cysts of the 3rd ventricle may also appear with this pattern.¹
  
• Tumor cysts from craniopharyngioma or Rathke’s cleft cysts may also be located in this region but should show a different density from that of CSF.
  
• Tumor cysts from hypothalamic astrocytomas should demonstrate a tumor mass in addition to a cystic component.
  
• Epidermoid or dermoid cysts should show a different density on fluid-attenuated inversion-recovery, but may also occur in this location.²

• Treatment options include1
  
  
  
  • Cyst fenestration, either open or endoscopic³
    
  • Cyst shunting procedure

• Endoscopic fenestration might be the procedure of choice (open cyst fenestration via craniotomy usually has not worked to manage this condition).^1,3
  
• Endoscopic third ventriculostomy may also be done in the same setting. See Fig. 61.2 and Fig. 61.3.
  
• The risks for this include standard anesthesia risks, risks of infection, and significant bleeding; however, these are low risks as for all intracranial surgeries.
  
• Specific to this surgery, risks of incomplete fenestration of the cyst, and recurrence of the cyst are possible. Cortical damage; intracranial hemorrhage; risk of seizures; damage to the fornix, the hypothalamus, or the basilar artery; or other uncontrolled intraventricular bleeding are also important risks to consider.

• The chance of success of this procedure is difficult to assess.
  
• Standard endoscopic third ventriculostomy for obstructive hydrocephalus might have a success rate as low as 40% in this age group, but successful fenestration of this cyst should have a more reliable duration of effectiveness.3,4

• If the initial procedure fails, open fenestration is an option, but the surgical approach is not without significant potential morbidity.
  
• Cystoperitoneal shunting of the cyst should relieve the obstructive hydrocephalus and would be the procedure of second choice.¹