Operative Planning

• Review imaging (magnetic resonance imaging [MRI], computed tomography [CT])
  
• Note degree of edema and enhancement pattern of lesion on MRI
  
• Note presence of calcium or hemorrhage within the lesion on noncontrast CT and MRI
  
• Note presence of hydrocephalus
  
• For radiographic visualization of tumor progression along optic tracts and radiations, consider use of specialized MRI sequences (i.e., fluid attenuated inversion recovery and diffusion tensor imaging)
  
• Radiographically define specific location of tumor relative to the third ventricle and chiasm
  
  
  
  • Lesions with predominant location confined to the optic chiasm
    
  • Lesions that destroy the chiasm and penetrate into the third ventricle
    
  • Lesions that grow predominantly into the third ventricle with only partial involvement of the chiasm
    
  • Lesions that originate from the floor of the third ventricle
    
  • Lesions that destroy the chiasm and grow along the optic tract without involvement of the third ventricle
  
  
• Endocrine function evaluation
  
• Ophthalmologic examination with visual field testing
  
• Diencephalic syndrome: a vigilant, emaciated infant or young child with macrocephaly, nystagmus, and visual deficits; cause of this characteristic syndrome is usually a large hypothalamic glioma producing hydrocephalus, optic neuropathy, and endocrine deficits
  
• Evaluate for neurofibromatosis type 1 (NF-1): tumors in children with NF-1 often remain stable for years after diagnosis

Special Equipment

• Cavitron ultrasound aspirator

Subfrontal Approach

• Consider orbital osteotomy
  
• For lesions with predominant location confined to the optic chiasm

Transcallosal Approach

• For lesions filling third ventricle with hydrocephalus

Combined (Frontal and Transcallosal) Approach

• For lesions involving both the chiasm and third ventricle

Pterional Approach with or without Orbitozygomatic Osteotomy

• For lesions extending laterally

External Ventricular Drain Placement

• Depending on extent of hydrocephalus, intraoperative or preoperative external ventricular drain placement is an important consideration

Gamma Knife Radiosurgery

• Gamma knife radiosurgery without open neurosurgical intervention may be appropriate for some lesions (e.g., treatment of hypothalamic hamartoma with gelastic seizures)

Tumor Resection

• Many lesions of the hypothalamus are low grade fibrillary astrocytomas with excellent long-term prognosis; therefore, emphasis should be placed on maintaining the integrity of normal structures when possible and resecting exophytic portion
  
• If preoperative testing has revealed a complete afferent pupillary defect in one eye, that optic nerve can be sacrificed to facilitate resection of a prechiasmal lesion
  
• For lesions with a significant cystic component, initial stereotactic aspiration of cystic fluid for relief of mass effect and improvement of intraoperative visualization is a consideration
  
• Diagnosis is confirmed with intraoperative review of frozen section by the neuropathologist
  
• Hemostasis of the resection cavity is methodically achieved with bipolar cautery, Avitene, Surgicel, or Gelfoam

• Slow steroid taper for high grade and recurrent lesions
  
• Shorter steroid taper for low grade lesions
  
• Antibiotics continued for 24 hours
  
• Visual fields assessed
  
• Endocrine function monitored
  
• Close monitoring for fluid status (i.e., diabetes insipidus or fluid retention)
  
• Close monitoring for development of hydrocephalus
  
• A postoperative MRI with and without contrast should be obtained within 48 hours for documentation of tumor resection and subsequent response to adjuvant therapy