53 Endoscopic Third Ventriculostomy and Biopsy of Pineal Region • Endoscopic third ventriculostomy (ETV) ◦ Symptomatic obstructive hydrocephalus. ◦ Patent subarachnoid spaces with adequate space between the clivus and the brainstem. ◦ Thinned/bowed floor of the third ventricle on sagittal MRI: – Indicates likelihood of safe fenestration of the floor. – Absence of this finding is not an absolute contraindication. • Pineal region biopsy ◦ Presence of a lesion in the pineal region or posterior third ventricle where pathologic diagnosis will significantly impact treatment options. ◦ Confirmation of absence of vascular lesion that would make biopsy contraindicated. • Position: The patient is positioned supine with the head placed on a gel donut or Mayfield horseshoe headrest. • Body: The body is placed supine with the arm boards or arms tucked at the side; a bilateral shoulder roll has to be used if head extension is desired for pineal region biopsy. • Head: The head is kept neutral or with a slight flexion. • The operating table is rotated 90 or 180° from anesthesia. • Monitors are placed at the foot of the bed for the operating surgeon and assistant. • A connection to the operating table for a pneumatic arm for the endoscope may be made. • Desired entry points are identified ◦ Laterality: Right side is preferred in most cases; though if one lateral ventricle is larger than the other, the larger ventricle is utilized. ◦ ETV: 1 cm anterior to the coronal suture at the mid-pupillary line. In infants with a patent anterior fontanelle, this can be marked at the junction of the fontanelle and the ipsilateral coronal suture ◦ Pineal region biopsy: Depending on the anatomy of the third ventricle and location of the lesion, a more anterior entry may be required. Simultaneous ETV and pineal region biopsy may require multiple burr holes or a single hole midway between both trajectories ◦ Neuronavigation: Particularly useful in pineal region biopsy to identify target intraoperatively and define entry, or to plan trajectory in patients with small ventricles or abnormal ventricular morphology. It can be used in any case for optimization of entry point • C-shaped or linear incision large enough to accommodate one or multiple burr holes is made (Fig. 53.1). • Identification of the midline. • Coronal suture. • Anterior fontanelle. • Skin is opened sharply. • Subcutaneous fat and galea may be opened sharply or with monopolar electrocautery. • Pericranium is opened with monopolar in the location of the entry point. • Care is taken to avoid injury to the anterior fontanelle when present. • Skin flap is retracted with suture or a self-retaining retractor. Fig. 53.1 Patient positioned supine on a Mayfield horseshoe head holder. Note the marking of midline and the C-shaped incision at the mid pupillary line. • Coronal suture. • Anterior fontanelle. • Entry point identification ◦ Repeat identification and update entry with neuronavigation, if utilized. ◦ Entry point is always identified anterior to the coronal suture. • Burr holes ◦ With patent anterior fontanelle, the entry point can be created using Kerrison punches at the anterolateral edge of the fontanelle. ◦ Without patent anterior fontanelle, the entry point is created with a pneumatic drill, Hudson brace, or hand twist drill with hole large enough to accommodate peel away sheath and endoscope. • Dura is opened in a cruciate fashion. • Bipolar electrocautery is used to coagulate dural edges ◦ Good hemostasis is important to prevent run down of blood products that would obscure view with endoscope. • Cannulation of ventricle (Fig. 53.2) ◦ The determination of depth is based on the measurement of cortical mantle on MRI preoperatively. ◦ Peel away sheath is inserted to depth adequate to just enter the ependyma of the lateral ventricle. ◦ The inner cannula is removed to confirm cerebrospinal fluid (CSF) flow. – CSF is sampled if a specimen is desired. – Endoscope is inserted for initial confirmation of ventricular access. – Sheath is peeled away to the appropriate depth and stapled to skin and/or drapes. ◦ Confirmation of side of entry. – Neuronavigation. – Anatomic landmarks. • Navigation of endoscope ◦ Identification of landmarks within the lateral ventricle (Fig. 53.3). – Foramen of Monro – Fornix – Choroid plexus – Septum pellucidum – Veins: Septal and thalamostriate ◦ Identification of landmarks within the third ventricle (Fig. 53.4) – Neural structures: Optic chiasm, tuber cinereum, hypothalamus, thalamus, inter-thalamic adhesion, habenular commissure, posterior commissure. – Arteries: Basilar artery, perforating branches. – Veins: Internal cerebral veins. – Recesses: Optic, infundibular, pineal, prepontine cistern. – Clivus. – Cerebral aqueduct. ◦ 0° Rigid endoscope is the most often utilized. – 30° Endoscope should be available if visualization is inadequate with the 0° scope. – Flexible scopes may be useful in cases of difficult trajectory, though optics are lower quality. ◦ Fenestration is performed anterior to the mammillary bodies and basilar apex at the midline. ◦ Basilar apex can be identified through thinned floor (tuber cinereum). ◦ If the floor is opaque, attempts at hydrodissection or endoscopic coring of the floor may still allow visualization and safe fenestration. ◦ Endoscope, blunt forceps, monopolar, laser, and Fogarty balloon have all been described as instruments used to make initial fenestration. – Use of monopolar and laser must be used cautiously due to risk of thermal injury to the underlying basilar artery. ◦ Widening of the fenestration can be done with inflation of a Fogarty balloon or spreading of blunt forceps.
53.1 Indications
53.2 Patient Positioning
53.3 Skin Incision
53.3.1 Critical Structures
53.4 Soft Tissue Dissection
53.4.1 Critical Structures
53.5 Craniotomy
53.6 Dural Opening
53.7 Intradural Exposure
53.8 Pearls
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