Septa in the Foramen of Monro
Direct Answer
The foramen of Monro does not contain septa as a normal anatomical structure; however, pathological membranous obstructions or septa can develop at this location due to congenital malformations, inflammatory processes, or post-surgical complications. 1, 2, 3
Normal Anatomy and CSF Flow
The foramen of Monro (interventricular foramen) serves as the communication pathway between the lateral ventricles and the third ventricle, through which CSF flows as part of normal circulation. 4, 5
- CSF flows from the lateral ventricles through the foramina of Monro into the third ventricle, then continues through the aqueduct of Sylvius to the fourth ventricle. 4, 5, 6
- This pathway is normally patent without any septations or membranes obstructing flow. 1
Pathological Septa/Membranes
Types of Obstructive Lesions
Membranous obstruction of the foramen of Monro represents an abnormal finding that can be:
- Congenital: Idiopathic membranous strictures present from birth, though often diagnosed later in life. 1, 7
- Inflammatory: Secondary to infectious processes such as neurocysticercosis, which can cause inflammatory obstruction. 8
- Post-surgical: Developing after endoscopic procedures like third ventriculostomy, where granulation tissue or membranous tissue forms across the foramen. 2, 3
Clinical Presentation
- Bilateral membranous obstruction causes marked dilation of both lateral ventricles with normal third and fourth ventricles, presenting with severe headaches. 1
- Unilateral obstruction results in isolated enlargement of one lateral ventricle (unilateral hydrocephalus). 8, 7
- Symptoms typically include headaches as the most common presenting complaint. 1, 8
Intraoperative Findings
When pathological septa are encountered during endoscopic exploration:
- Thick, tough granulation tissue may cover the foramen following previous surgical interventions. 2
- Thin membranous tissue can occlude the foramen in idiopathic or congenital cases. 2, 7
- Bilateral membranous obstruction with auto-fenestrated cavum septum pellucidum has been documented. 1
Treatment Approach
Endoscopic fenestration is the preferred first-line treatment to avoid permanent shunt placement:
- Endoscopic foraminoplasty involves perforating the obstructing membrane to restore CSF flow. 2, 3
- Septostomy (fenestration of the septum pellucidum) may be performed concurrently to allow communication between lateral ventricles. 1, 3, 8
- Stent placement through the fenestrated foramen can maintain patency in cases of recurrent obstruction. 2
- Ventriculoperitoneal shunt placement is reserved for cases where endoscopic treatment fails or is not feasible. 1
Key Clinical Pitfall
The most important caveat is that membranous obstruction of the foramen of Monro can develop years or even decades after initial endoscopic procedures (up to 20 years post-ETV), requiring long-term surveillance in patients with treated hydrocephalus. 3