31 Endoscopic Exploration and Biopsy of Basal Cisterns



10.1055/b-0036-142006

31 Endoscopic Exploration and Biopsy of Basal Cisterns

José Juan Sánchez Rodríguez, Jaime Gerardo Torres-Corzo, and Leonardo Rangel-Castilla


31.1 Introduction


Neuroendoscopy has revolutionized the management of hydrocephalus since the mid-1990s. Endoscopic procedures like endoscopic third ventriculostomy (ETV) are the treatment of choice for most cases of obstructive hydrocephalus.1,2,3,4,5,6 Neuroendoscopy, as a diagnostic tool, has allowed a better understanding of the causes and mechanisms that result in hydrocephalus.4,5 However, neuroendoscopic exploration should not be limited to the ventricles as it is possible to access the subarachnoid space of the basal cisterns transventricularly, particularly with a flexible neuroendoscope.7,8,9,10,11 The interpeduncular, prepontine, and prebulbar cisterns can be reached through an ETV,4 and the cisterna magna through the foramen of Magendie of the fourth ventricle.12 This method has enabled neurosurgeons to explore, diagnose, and conduct procedures inside the basal cisterns safely. These procedures include biopsies,4,13 parasitic extraction5 (see Chapter 28), and biopsy of exophytic brainstem cerebral gliomas,14 among others. Basal cisterns can be affected by infectious, auto-immune, granulomatous, and other disorders that can result in basal meningitis with adhesive arachnoiditis and subsequent hydrocephalus.15,16,17 Chronic meningitis and other granulomatous diseases affect the basal cisterns more than the rest of the arachnoid spaces, so diagnosis can be a challenge especially when biopsies are not taken from affected areas (cortex).4 Simultaneously, secondary hydrocephalus can be treated with endoscopic procedures.4,10,11,18 This chapter will review in detail the indications, operative technique, results, clinical outcome, and possible complications of endoscopic transventricular basal cistern exploration and biopsy.



31.2 Indications/Contraindications


Transventricular arachnoid biopsy of the basal cisterns is indicated on patients with chronic meningitis of uncertain diagnosis that despite empiric treatment has had no clinical improvement. Diagnostic work-up includes magnetic resonance imaging (MRI) demonstrating enhancement of the basal cisterns, with or without hydrocephalus, and negative cerebrospinal fluid (CSF) from repeated lumbar punctures (gram, culture, immunologic, and molecular tests).4,9 Thoughtful exploration of the basal cisterns and ventricular system should be performed if necessary. Exploration should include at a minimum the interpenducular and prepontine cisterns, Liliequist’s membrane, both lateral ventricles, and the third ventricle. Exploration of the cerebral aqueduct, fourth ventricle, and cisterna magna is done only when feasible and by an experienced neuroendoscopist4,10,11,12 (see Chapters 27 and 28). Ventriculomegaly is not a requisite for transventricular basal cistern exploration. Endoscopic exploration in pediatric and adult patients with normal ventricular size has been demonstrated to be safe and feasible.1,19,20


Exploration of the basal cisterns is also indicated for patients with intraventricular neurocysticercosis. The presence of parasites may not be evident on neuro imaging, and exploration of the basal cisterns for parasites is necessary5,9 (see Chapter 28).


It is important to be familiar with the term frozen subarachnoid space, a direct endoscopic finding mentioned in the literature. It refers to severe adhesive arachnoid bands attached to the basilar artery and clivus, diminishing the average visible pulsations of the basilar artery; this phenomenon was named “frozen” subarachnoid space due to the immobile appearance of the vasculature.4 This endoscopic finding is determined during the neuroendoscopy posterior to endoscopic third ventriculostomy and no specific measuring method is used to make this differentiation.4 The frozen subarachnoid space plays an important role in predicting the efficacy of ETV, and it can prevent further exploration down into the basal cisterns.21 This is common for patients with chronic meningitis.4,21


Contraindications for basal cistern exploration are patients with aneurysms of the arteries of the skull base and severe anatomical abnormalities that do not allow differentiating the third floor ventricle structures.9,11 Taking an arachnoid biopsy in the pier of the cisterna magna is contraindicated in patients with complete agenesis of the cerebral aqueduct and the foramen of Magendie.9,11



31.3 Operative Technique



31.3.1 Preoperative Preparation


The procedure is performed under general anesthesia with the patient in the supine position. The patient’s head should be in neutral standing and flexed at 20 to 30º.4,5,7,8,9,10,11,12 The side chosen for the approach is based on the characteristics of each patient and the imaging studies, but the right side is preferred. The bur hole is placed at the standard Kocher’s point.4,5,7,8,10,11,12 We only perform this procedure with the flexible neuroendoscope. It is possible to take a transventricular arachnoid biopsy using a rigid endoscope, usually limited to the interpeduncular and prepontine cisterns. A flexible neuroendoscope also allows for transaqueductal exploration of the fourth ventricle and the cisterna magna.4,10,11,12 The use of a rigid endoscope is contraindicated for transaqueductal exploration. Before inserting the endoscope into the ventricle, we recommend taking a biopsy of the cerebral cortex with adjacent meninges and a ventricular CSF sample.4



31.3.2 Description of Procedure


Once the endoscope is in the lateral ventricle, the foramen of Monro is identified and the third ventricle is accessed. The ETV is performed in a standard fashion (see Chapter 21). It is important to observe the characteristics of the ependyma covering the ventricles and the premammillary membrane, since these have been suggested as a prognostic factor of ETV in infectious diseases.21 The ETV size has to be sufficiently extended to permit the passage of the endoscope; if the Liliequist’s membrane is closed, it must also be opened.4,10 Introduce the endoscope through the fenestration carefully into the interpeduncular cistern in front of the basilar artery, preventing direct contact of the tip with the basilar artery and avoiding tearing of the perforating arteries located in the cistern (Video 31.1). Carefully navigate through the interpeduncular cistern to the prepontine cistern (between the basilar artery and clivus) and the prebulbar cistern, following the ventral part of the basilar artery and the junction of the vertebral arteries (Video 31.1).4,11 During this exploration of the characteristics of the arachnoid, blood vessels, and nerves observe for signs of inflammation, permeability of the subarachnoid space, CSF flow, and the presence of exudates or granulations. Arachnoid biopsy is performed by gentle traction on arachnoid, preferably arachnoid membranes and trabeculae, with a grasping forceps4 (Fig. 31.1). If any particular area is seen to be more inflamed or to have more exudates, it is important to take a biopsy at that site if possible (respecting the neurovascular structures of the skull base). To take a biopsy of the cisterna magna, the fourth ventricle is approached by the endoscope through the foramen of Magendie and then navigated. The technique is described in Chapters 27 and 28, and the biopsy is taken in the same way as described there. In this procedure, it is important not to damage the posterior inferior cerebellar arteries subsequent to passing through the foramen of Magendie.4,12

Fig. 31.1 Endoscopic views (a) of prepontine and prebulbar cisterns affected with adhesive arachnoiditis and exudates; (b) biopsy in area with exudates; (c) closeup of the biopsy site; (d) cottonlike exudates; (e) new target site for biopsy; (f) clamps taking arachnoid fragment during biopsy; (g) clamps with arachnoid fragment after biopsy; (h) biopsy site of (f) and (g); no bleeding or lesions are observed.
Video 31.1 Endoscopic basal cistern exploration and biopsy (flexible neuroendoscope). This intraoperative endoscopic video demonstrates an exploration of the basal cisterns and biopsy in a patient with infectious arachnoiditis. The endoscope is introduced into the right lateral ventricle and third ventricle. Reactive inflammatory granular nodules are observed on the ependymal wall. An endoscopic third ventriculostomy is performed using standard technique. The floor of the third ventricle is abnormally thick secondary to the chronic inflammatory process. The flexible endoscope is passed into the basal cisterns. Arachnoiditis and cottonlike exudates are observed on the arachnoid layers. Using a biopsy forceps, specimens of the arachnoid are taken. Observe the reactive inflammatory process of the basilar artery. Specimens are obtained from multiple locations of the basal cisterns. Arachnoid adhesions are released to clear basal cisterns and permit adequate CSF flow. The endoscope is advanced into the premedullary cistern. Arachnoiditis is again observed around the vertebral artery and lower cranial nerves. After a complete exploration, the neuroendoscope is carefully withdrawn.

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Jun 1, 2020 | Posted by in NEUROSURGERY | Comments Off on 31 Endoscopic Exploration and Biopsy of Basal Cisterns

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