The patient was taken to surgery. A tumor was expanding the medulla oblongata, deforming the anatomy, and displacing the midline (Fig. 59.3). Using neuronavigation, the area closest to the surface was the point used for entry.

On the frozen section, the patient’s specimen confirmed a diagnosis of juvenile pilocytic astrocytoma.

• CT scan reveals a grossly enlarged hypodense brainstem with no evidence of hydrocephalus. The hypodensity appears to be reaching the foramen magnum.
  
• The MRI shows a nonenhancing lesion best seen on fluid-attenuated inversion-recovery (FLAIR) study showing a medullary epicenter with minimal if any ventral lateral medulla identified on the right side. The lesion respects the boundaries of the medulla both caudally and rostrally.

• Differential diagnosis includes benign or malignant brainstem tumor. Benign brainstem tumor is favored by the long history without multiple cranial nerve involvement, a respect of the boundaries of the medulla, and a medullary location as opposed to a pontine location.
  
• Benign masses in this location can include pilocytic astrocytoma. Less likely diagnoses include hemangioblastoma, pleomorphic xanthoastrocytoma, and a brain abscess.
  
• Malignant tumors in this location include glioblastoma multiforme, metastases, and lymphoma.^1–3

• Important studies to obtain are swallowing studies, overnight sleep study, and vocal cord assessment by otolaryngology examination. ⁴

• Given the probable benign nature of this lesion, despite its size based on clinical presentation and location, an initial approach should be to obtain a tissue sample (based on imaging studies, the tumor consistency appears to be diff erent from the surrounding brainstem).

• The approach should be done in prone position with some neck flexion with the use of a suitable pediatric head frame to stabilize the head for surgery.
  
• Obtaining accurate neuronavigation information is essential.
  
• Additionally, multimodality evoked potential monitoring should be utilized.
  
• The lesion should be approached through the eroded floor of the 4 th ventricle, if such an area can be identified. 0therwise, relatively safe entry zones should be used.
  
• Given the extension and size of the lesion on the left side, a far lateral approach may also present a less morbid option for resection of this tumor.
  
• Given the finding and the presence of a presumably acceptable distinct appearance of the tumor, a significant debulking taking care to allow for reexpansion of compressed tissue should be done with careful monitoring of vital signs and evoked potentials.
  
• If the walls of the lesion appear to show pulsations that would suggest thinning of the wall, particularly on the left anterior aspect, the procedure should be terminated. A significant but subtotal resection would be sufficient in this case.⁴

• The MRI obtained postoperatively shows a central cavity of resection with a significant amount of residual tumor despite the significant reduction in the total volume of the tumor. There is reexpansion of the brainstem, particularly on the right side.
  
• The patient is doing well; therefore, he may be able to sustain another surgical procedure.
  
• With sufficient time to allow reexpansion toward the central cavity, a second approach via the initial myelotomy tract to obtain further significant resection could be contemplated. ⁵

• A more expectant approach is also an option given the benign nature of the tumor (although we do not favor this option for the reasons stated above).⁶
  
• Alternative treatment plans also include radiotherapy and chemotherapy.
  
  
  
  • Both are associated with significant morbidity at this age and would not represent, at this point, a preferred option given the fact that the patient tolerated the surgery well.^5,7

• Given the benign histology, the slow progression, and the fact that the brainstem is showing reexpansion, the prognosis, although guarded because of the location of the lesion, should be favorable.
  
• This also favors the possibility of further intervention and close follow-up.
  
• The preferred recommendation would be for return surgery through the same myelotomy approach into the brainstem.8–10
  
• Some might recommend, prior to repeat surgery, chemotherapy in an attempt to reduce the tumor burden and then a second look at surgery. This has been advocated for choroid plexus papillomas, as well as some ependymomas.¹¹

• The goal of a second surgery would be further debulking, taking care to avoid significant morbidity in the lower brainstem in particular.
  
• Further tumor reconfiguration toward the cavity would favor a return for surgery.

• Returning a second time could risk some lower cranial nerve difficulties, which can be avoided by staying in the center of the lesion.
  
• Additional risks include the development of hydrocephalus following a second surgery in the posterior fossa.
  
• There is an increased risk of cerebrospinal fluid fistula development in the context of a second duraplasty.
  
• Additional risks include meningitis, posterior fossa hematoma, infection or abscess, poor healing, etc.

• If the histology remains the same and the patient remains stable clinically after further debulking, the recommendation would be for careful observation with baseline MRI scans being done at approximately a 2-month interval. All three treatment options discussed previously remain viable for the future. ⁷

• Not all brainstem gliomas have the same prognosis.
  
• Having the epicenter of the lesion within a non-pontine territory of the brainstem is a favorable prognostic factor.
  
• A prolonged history and a focal positive neurologic examination are favorable prognostic factors. ⁹
  
• Uniformity of the signal within the tumor on imaging studies, either as uniform enhancement or as a FLAIR high signal, represents a favorable factor.
  
• Growth pattern limited to a segment of the brain-stem and, in particular, a deviation toward the floor of the 4 th ventricle are favorable factors. This growth pattern may be either from a dorsal exophytic brainstem tumor or a cervicomedullary tumor, and its limitation suggests restriction of growth by existing ventral corticospinal fibers of the pons or the cervical medullary junction. ¹²
  
• The presence of a cyst is also a favorable factor.
  
• Noninfiltrative tumors if approached with care can be significantly debulked with microsurgical technique and the use of multimodality evoked potential monitoring.