The Operation – Options
Cranial cyst shunting
Shunting carries a lower surgical risk than cyst fenestration, but it results in the need for lifelong care of the shunt and in the risks of shunt infection, malfunction, and overdrainage. The use of a programmable valve can be considered to lessen the risk of rapid overdrainage. Shunting is considered as a primary or secondary procedure, as follows:
- Primary procedure if hydrocephalus present: When cysts are seen in a setting of macrocephaly in an infant or ventricular enlargement in an older child, there is a high likelihood of associated hydrocephalus. In these cases, shunt placement has a higher rate of success and a lower rate of complications.
- Secondary procedure when fenestration fails: Repeat fenestration after a failed initial fenestration has a low likelihood of success. In these cases, shunt placement should be considered if the cyst remains symptomatic or continues to enlarge.
Cranial cyst fenestration
Fenestration is the most common intervention for enlarging cysts. It tends to balance the pressure gradients between the cyst and intracranial CSF spaces unlike shunts, which may create a pressure gradient. The procedure is considered definitive when successful and reoperations are avoided. The fenestration can be accomplished in two ways:
- Microsurgical fenestration: The surgical microscope is used to fenestrate the cyst into CSF spaces such as the basal cisterns in the case of middle fossa cysts or other subarachnoid spaces for cysts in other locations.
- Endoscopic fenestration: Fenestration is done while visualizing the work with an endoscope. The opening in the skull bone is typically smaller; thus the procedure is less invasive, but there is a higher risk of inadequate fenestration.
- Surgery if cyst growing or symptomatic: Surgical resection is indicated when spinal cysts are growing or symptomatic. The goal of surgery for extradural cysts is drainage of the cyst and repair of the dural tear. In cases of intradural cysts, the cyst should be fenestrated via open laminectomy and the surgeon should ensure free flow of CSF in a cephalocaudad direction.
- Observe when asymptomatic: Observation is all that is required when a spinal cyst is asymptomatic.
- Patient position so craniotomy superior: The patient is positioned prone so that the cyst is at the highest point possible.
- +/- Head holder
- Scalp incision over cyst
- Dural opening over the cyst: Care is taken to avoid injury to the underlying veins.
- Cortical incision when needed: When the cyst does not come to the surface or when it is not accessible via extracerebral dissection, it is reached via a transcortical approach.
- Laminotomy/laminectomy: A laminectomy for cyst fenestration is performed. This allows maximum exposure and fenestration. Laminotomies can be considered for small cysts if it can be ascertained that there is free flow of CSF around the collapsed cyst at the conclusion of the case.
- Communicate cyst with CSF circulation: The cyst is optimally fenestrated into the subarachnoid space, typically the basal cisterns or an adjacent ventricle. Care should be taken that there is free flow of cyst fluid into the subarachnoid space, without any intervening webs.
- Extradural cysts: Extradural cysts usually have a connection to the intradural space at a nerve root and require a dural closure at the point of communication. Myelography can show this connection, thereby allowing a smaller laminectomy and simple ligation.
- Intradural cysts: If the cyst is intradural, the walls are resected except for the portion that is adherent to the spinal cord. That portion is not removed in order to avoid damaging the cord.
- Cyst shunting: Shunting may be used for recurrent cysts.
- Eliminate air within cyst: The resection cavity is filled with irrigation fluid after complete hemostasis. The authors occasionally place oxidized surgical cellulose intradurally to lower the risk of CSF leak.
- Close dura and routine closure: The dura is tightly closed, Grafts may be used as indicated. Routine craniotomy and scalp closure are used.