23.1 Introduction

When treating patients with hydrocephalus, neuroendoscopic procedures offer the chance to fenestrate different membranes, create alternate cerebrospinal fluid (CSF) pathways, remove obstructing lesions, or re-establish normal pathways of CSF flow.1,2

The use of endoscopic methods to create pathways for CSF between ventricles, membranes, and the subarachnoid space, or between tumors and the ventricular system has become the treatment option of choice.3 Thus, neuroendoscopy is a frequently used alternative to ventriculoperitoneal shunt placement and open surgery.2,4,5

Septum telencephali is a term introduced by Andy and Stephan6 to denote the midline structure located in the rostral telencephalon and divided into two compartments: a superior portion (septum pellucidum [SP]) enclosed by a thin membrane and containing glial cells and fiber bundles, and a caudal portion (septum verum).5,6 The SP is a thin, bilaminar translucent sheet (pellucidum means transparent). Located between the lateral ventricles, it extends from the genu and rostrum of the corpus callosum to the superior surface of the fornix, and from the lamina terminalis to the splenium of the corpus callosum.5,7,8

The main options for treating patients with monoventricular hydrocephalus (MH) are to create fenestrations using a neuroendoscopic approach, place CSF shunts, or perform open surgery.3,9 Shunts are generally considered the simplest treatment option, although high revision rates have been reported, especially in infants, those with infectious diseases, and cases related to arachnoiditis. A neuroendoscopic septum pellucidum fenestration (SPF) allows the passage of CSF from one lateral ventricle to the other—from the side with the higher pressure to the side with lower pressure (Fig. 23.1, Video 23.1, Video 23.2, Video 23.3, and Video 23.4).5 This procedure offers an alternative to shunt placement and open surgery for patients with MH,1,5 and its use has a record of low morbidity and good results in selected patients.1,9

23.2 Indications/Contraindications

The ideal indication for a septostomy is an obstruction of the foramen of Monro (FOM).2,10 The SP forms the medial wall of the frontal horn, body, and atrium.5 Abnormalities in the SP are seen in 0.3 to 1.75% of normal computed tomography (CT) scans. The most common lesions in the SP are cysts followed by tumors. The prevalence of cysts is 10 to 15% in autopsies. Cysts are related to incomplete SP cavity obliteration and are usually an anatomical variation.11 In most cases, the cyst is connected to the ventricles and the CSF flows back and forth from one structure to the other. A cyst of the septum pellucidum (CSP) is also called the “fifth ventricle” or cavum vergae.12

Almost all patients with a CSP are asymptomatic.13 When symptoms are present, they are caused by an increase in intracranial pressure (ICP) and hydrocephalus; these conditions may result from the cyst obstructing the CSF flow at the level of the FOM, which in turn leads to MH.

MH has been observed in patients of all ages, including fetuses, premature infants, neonates, children, and adults. The etiologies of MH can be congenital (e.g., cavum vergae) or acquired (e.g., ventriculitis secondary to infection or following hemorrhage, tumors, or cysts).9

Sign and symptoms of MH include headache, emesis, loss of consciousness, sensorimotor disturbances, and other complaints.14,15 The increased ICP with compression of the optic nerve can result in symptoms such as abducens nerve palsy, nystagmus, papilledema, retinal hemorrhage, partial or total loss of vision, and visual field defects.12 In addition, the SP is an important relay station linked with the hippocampus, hypothalamus, and the limbic system.5 The symptoms patients experience as a result of mass effect in this region include behavioral, autonomic, and sensorimotor disturbances; mental status changes; memory impairment; seizures; emotional lability; and frontal ataxia.12

Today, the main options for treating MH are shunts and neuroendoscopic surgery. As mentioned before, due to the high rates of complications including infection and revisions, the use of ventriculoperitoneal shunts in this condition are not favored.3,9,14,16,17 The neuroendoscopic technique allows a physiologic restoration of the CSF flow through a natural or created pathway; it is minimally invasive and does not require permanent implants.1,2,9

Surgical opening of the SP, as a stand-alone endoscopic procedure, is used primarily to treat isolated lateral ventricle enlargement. This condition involves one collapsed and one grossly dilated ventricle, thereby significantly distorting the anatomy and increasing the degree of difficulty associated with this procedure.18

Although there are not many contraindications for SPF, one absolute contraindication is acute hydrocephalus. The success of the SPF is directly related to the etiology of the hydrocephalus, history of intraventricular hemorrhage, and other factors associated with thickening of the septum.10