The foramen of Magendie: a comprehensive review of its history, anatomy, pathology, and surgical approaches

Abstract

The foramen of Magendie (FOM), or median aperture, represents a critical anatomical structure allowing cerebrospinal fluid outflow from the fourth ventricle into the cisterna magna. Since its description by François Magendie in the 19th century, its existence, embryological development, and clinical importance have been subjects of debate and refinement. This review synthesizes the historical context, developmental biology, and anatomical nuances of the FOM, alongside its involvement in congenital and acquired pathologies, particularly Blake’s pouch cysts, Dandy–Walker malformations, and obstructive neoplasms. We further analyze controversies surrounding its recognition in early literature, anatomical variants including agenesis, and its surgical implications. Surgical approaches such as the telovelar and transvermian routes are compared, with emphasis on minimizing morbidity while ensuring exposure. Advances in neuroimaging and microsurgical technique have reinforced the FOM’s relevance in modern neurosurgery. A comprehensive understanding of its anatomy, pathology, and historical discourse is essential for anatomists, neurosurgeons, and clinicians managing posterior fossa pathologies.

Introduction

The brain’s ventricular system contains cerebrospinal fluid (CSF), which is generated primarily from the choroid plexus [1]. In healthy physiological states, CSF travels from the paired lateral ventricles to the third ventricle by the interventricular foramina (of Monro). It continues to flow from the third to the fourth ventricles via the cerebral aqueduct (of Sylvius). It finally exits the fourth ventricle to continue into the cisterna magna. CSF can exit the fourth ventricle via three structures. The foramen of Magendie (FOM), or median aperture, is the single median pathway for CSF flow exiting the fourth ventricle to the cisterna magna (Figs. 1–3) [2]. The two lateral apertures or foramina of Luschka allow for egress of CSF into the cerebellopontine angle (Fig. 1).

Fig. 1.

Drawing illustrating the region of the foramen of Magendie (red circle). FH, right frontal horn; left and right foramina of Monro (arrows); III, third ventricle; CA, cerebral aqueduct; OH, left occipital horn; TH, left temporal horn; IV, fourth ventricle.

Fig. 2.

The foramen of Magendie seen in two cadaveric specimens (*).

Fig. 3.

Cadaveric specimen with retractors placed to better view the inferior medullary velum and foramen of Magendie (*). Courtesy Dr. Albert Rhoton.

This comprehensive paper provides a comprehensive review of the FOM, from its origins in the embryo to its pathological relevance and a historical context to explain how anatomists have come to understand the structure in its entirety. This information has clinical significance owing to the foramen’s involvement in certain congenital and acquired disease states.

The protocol of the study did not require approval by the ethical committees or informed consent. The study followed the Declaration of Helsinki (64th WMA General Assembly, Fortaleza, Brazil, October 2013).

Embryology

The FOM develops as follows. The neural tube forms during the fourth week of gestation [3]. It is closed dorsally by the end of the fourth week of gestation, remaining open only at its rostral and caudal ends: the rostral and caudal neuropores [4].

Three main vesicles form near the rostral end of the neural tube. Cavities within these vesicles will develop into the mature ventricular system, as described in the introduction. The vesicle in the rhombencephalon develops into the fourth ventricle.

After the closure of the caudal neuropore during weeks 5–6 of gestation, the rhombencephalon splays dorsally, and the roof plate stretches to create the tent-shaped fourth ventricle [5]. Around weeks 10–12, fenestrations begin to form in the tela choroidea of the fourth ventricle (known at this stage of development as Blake’s pouch) [6]. These individual fenestrations expand through week 16 of gestation, at which point they have matured into a single aperture: the FOM. Failure of these fenestrations to develop can lead to forming a Blake’s pouch cyst, described in the “Pathology” section below [7].

Anatomy

Understanding the anatomical position of the FOM first requires a detailed depiction of the positioning of the fourth ventricle (Fig. 1). This ventricle is best characterized as tent-shaped and is located between the cerebellum posteriorly and the brainstem anteriorly. It has a roof, a floor, and two lateral recesses. The roof begins rostrally at the terminus of the cerebral aqueduct and ends caudally at the FOM. The apex of this “tent,” also called the fastigium, provides the unofficial dividing point between the superior and inferior portions of the fourth ventricle [8].

The FOM is the largest opening of the fourth ventricle; the diameters of the cerebral aqueduct and the lateral foramina of Luschka are smaller. This aperture is approximately 6 mm in diameter [9]. It is located at the level of the inferior medullary velum and sits opposite the obex of the brainstem anteriorly and the cerebellar vermis posteriorly (Fig. 4) [10]. It is bordered superolaterally by the tela choroidea (Fig. 5) [11].

Fig. 4.

Intraoperative microscopic identification of the region at and around the foramen of Magendie. (A) Zoomed out view (white arrows: posterior inferior cerebellar arteries, white asterisk: choroidal plexus of the fourth ventricle, black asterisks: striae medullaris, white dashed line: cerebral aqueduct opening). (B) Zoomed in view (white arrows: posterior inferior cerebellar arteries, white asterisk: choroidal plexus of the fourth ventricle, black asterisks: striae medullaris, blue arrow: cerebral aqueduct, white dashed line: cerebral aqueduct opening). (C) Slightly zoomed out and focused on the floor of the fourth ventricle (white arrow: posterior inferior cerebellar arteries, black asterisks: striae medullaris, blue arrow: cerebral aqueduct, white dashed line: cerebral aqueduct opening). (D) Zoomed in and focused on the floor of the fourth ventricle (black asterisk: striae medullaris, blue arrow: cerebral aqueduct, white dashed line: cerebral aqueduct opening).

Fig. 5.

Brain magnetic resonance imaging sequences showing the foramen of Magendie (yellow dashed line). (A) Sagittal constructive interference in steady state sequence (red arrow: posterior inferior cerebellar artery; red asterisk: choroidal plexus of the fourth ventricle, blue arrow: cerebrospinal fluid flow passing through the foramen of Magendie), (B) axial T2-weighted sequence. (C, D) Cine phase-contrast magnetic resonance imaging (blue arrows: cerebrospinal fluid flow passing through the foramen of Magendie).

History

This foramen is named after François Magendie (1783–1855), a French anatomist who described it after researching CSF flow in human cadavers during the early 1820s.

François Magendie (Fig. 6) made groundbreaking contributions to physiology, neuroanatomy, and pharmacology [12, 13]. However, his recognition in non-French literature remains limited. Our review highlights his significant impact on the emerging field of neurosurgery. He employed Galvanic current to treat neuralgias and vivisected cranial nerves to understand their functions, devised a method to extract CSF, and detailed its properties in normal and pathological states [14]. Magendie accurately described the roles of posterior and anterior rootlets using vivisection and discovered the sensitivity of the meninges to pain [12]. His identification of the foramen, now named after him, is discussed here.

Fig. 6.

François Magendie. Image source: Wikimedia Commons (Public Domain) [13].

Born on October 6, 1783, in Bordeaux, Magendie died on his birthday in 1855. He witnessed significant events like the occupation of Paris, the Hundred Days, and Waterloo. Following his father’s path, he became a well-trained surgeon and later an experimental physiology pioneer [15, 16].

At sixteen, too young for the École de Santé, Magendie apprenticed at the Hôtel-Dieu under surgeon Baron Alexis de Boyer. In 1803, Magendie became a medical student at the Hôpital Saint-Louis. By 1807, he was an anatomy instructor at the École de Médecine. He earned his medical degree in Paris on March 24, 1808 [12].

Magendie’s first post-thesis publication appeared in the Bulletin des Sciences Médicales, commemorating anatomist Marie François Xavier Bichat [17]. In 1811, he became an anatomy demonstrator at the Faculté de Médecine in Paris, teaching anatomy, physiology, and surgery for three years. In 1826, he became Médecin adjoint at the Salpêtrière and chair of medicine in 1831 at the Collège de France.

Magendie’s neuroanatomical research included significant observations of the retina, thalamus, and cerebral peduncles’ roles in movement. He found that the cornea was innervated by the trigeminal nerve. His most significant yet controversial contribution was distinguishing sensory and motor nerves in the spinal cord, contemporaneously with English anatomist Charles Bell.

Magendie was infamous for his pivotal yet controversial public vivisections. His live dissections, such as the notorious public dissection of a dog, influenced animal cruelty laws in Britain. In 1824, he demonstrated cranial nerve vivisection methods, which advanced the understanding of nerve functions despite being condemned for their brutality. Magendie debated the origin of CSF and documented its flow from the fourth ventricle into the subarachnoid space through the FOM [18].

Controversy

There has been much debate about whether the FOM is real [19-21]. Magendie first described his ventricular findings to the Academy of Sciences in Paris in 1828. His landmark book and accompanying atlas, Recherches physiologiques et cliniques sur le liquide céphalo-rachidien ou cérébro-spinal (Physiological and clinical investigations about the cerebrorachidian or cerebrospinal fluid), published in 1842, formally detailed the FOM. Before this publication, the most detailed descriptions of the fourth ventricle had been rooted in animal studies by Galen during the Roman era and human studies by anatomists such as Vesalius and Cotugno during the Renaissance era. Magendie’s foraminal “discovery” of the mid-1800s was a rediscovery of the structure detailed by Vesalius and others [22].

Nevertheless, his work was rejected by many nineteenth-century anatomists [23]. The most prominent of this group were Monro, Krause, Todd, Virchow, and Reichert [9, 15, 16]. However, Magendie’s research was notably confirmed by German anatomists Axel Key and Magnus Gustaf Retzius in 1875 [20]. These researchers injected fluid into cadaver ventricular systems to demonstrate flow into and out of the fourth ventricle, which corroborated the existence of the FOM. In 1931, Rogers [21] defined the median aperture as a deformity in the roof of the fourth ventricle. Most major anatomical atlases and textbooks display the FOM as a perforation in the inferior medullary velum, as reviewed by Spierer [8]. This is consistent with Magendie’s description.

Pathology

Two common categories of pathology affect the FOM: neoplastic obstruction and cystic malformations. Their common consequence is hydrocephalus due to impaired CSF egress from the fourth ventricle.

Tumors

Ependymomas, subependymomas, and medulloblastomas are the most frequent neoplasms of the fourth ventricle [24]. By encroaching on or obstructing the FOM, they impair CSF circulation. Computed tomography and magnetic resonance imaging can aid differentiation: ependymomas are often hyperdense with heterogeneous enhancement, subependymomas are iso-/hypodense and usually non-enhancing, and medulloblastomas typically appear hyperdense with uniform enhancement and can fill the ventricle. Histological confirmation is essential. Surgical excision, usually via midline suboccipital craniectomy, remains the mainstay.

Congenital and cystic anomalies

Dandy–Walker malformations exemplify developmental anomalies involving the posterior fossa, characterized by vermian agenesis, fourth ventricular cystic dilation, and hydrocephalus [25]. Variants of this malformation spectrum frequently impact the FOM. Blake’s pouch cyst, arising from failed fenestration of the tela choroidea during gestation, results in persistent cystic dilation and vermian hypoplasia [7]. While some patients re-expand the vermis after shunting, persistent obstruction requires intervention such as ventriculoperitoneal shunting or endoscopic third ventriculostomy (ETV).

Anatomical variants

Agenesis of the FOM has been described in surgical series. Cruveilhier [26] reported an absence in 2% of cases, and Tubbs [27] observed surgical cases of agenesis. Other variants include septations, arachnoid veils (Fig. 7) obstructing CSF pathways, and partial duplications [28, 29]. Such anomalies complicate both radiological interpretation and surgical access. Their presence underscores the importance of individualized preoperative imaging.

Fig. 7.

Arachnoid veil covering the foramen of Magendie.

Surgical Approaches

There are three main surgical approaches to the FOM: the direct approach, the transvermian approach and the telovelar approach (TVA), each involving a midline suboccipital craniectomy.

The direct approach simply spreads the cerebellar tonsils, identifies the FOM and enters this corridor into the fourth ventricle (Figs. 4, 8). Such approaches are used, for example, to verify CSF egress out of the fourth ventricle during posterior fossa decompression in patients with Chiari malformations, especially in the face of concomitant syringomyelia.

Fig. 8.

Intraoperative direct approach through the cerebellar tonsils into the fourth ventricle via the foramen of Magendie.

The transvermian approach splits the cerebellar vermis in the midline. In this exposure, the inferior vermis is incised up to the level of the fastigium of the fourth ventricle, and the two halves of the vermis are retracted to opposite sides. This provides wider and more rostral exposure than the TVA. Still, it is riskier because it can cause caudal vermis syndrome (truncal ataxia, disequilibrium, and nystagmus) and cerebellar mutism [30]. The transvermian approach is therefore relied upon far less frequently in the modern clinical setting.

In contrast, the TVA advances through the cerebellomedullary fissure without incision of the vermis. The cerebellar tonsils are separated and blunt dissection is carried out between the tonsil and the adjacent uvula on the side of the procedure (or bilaterally if the surgeon needs this type of access) [31]. Once the tonsil and uvula are retracted, the surgeon must identify and protect the posterior inferior cerebellar artery (PICA) and its branches. The operating window in this approach is narrower than in the transvermian approach, but the lack of tissue dissection reduces the risk of caudal vermis syndrome and cerebellar mutism [32]. This approach is, therefore, more commonly used in the modern clinical setting.

In both approaches, the surgeon must identify and protect the floor of the fourth ventricle once the operating window has been established to avoid injuring the posterior pons and medulla oblongata.

ETV can be applied in cases where surgical resection of a tumor or cyst is not deemed necessary, but the clinical symptoms of hydrocephalus must be relieved.

The FOM serves as a vital outflow tract for CSF circulation. Its embryological origins, debated history, and surgical relevance highlight its central role in neurosurgical practice and neuroanatomical research. Recognition of its anatomical variants and pathological involvement—ranging from congenital cysts to obstructive tumors—remains essential for accurate diagnosis and safe intervention. Modern imaging techniques, coupled with refined surgical approaches such as the telovelar method, have reduced morbidity while improving exposure and outcomes. Beyond its clinical significance, the FOM illustrates the evolution of anatomical knowledge, from Magendie’s contentious 19th-century observations to its current acceptance as a cornerstone in ventricular anatomy. An understanding of the FOM is important for anatomists and clinicians addressing posterior cranial fossa disease.