What is the infundibulum of the brain?

The Infundibulum of the Brain: Anatomical and Clinical Significance

The infundibulum of the brain is a funnel-shaped stalk that connects the hypothalamus to the pituitary gland, serving as a critical pathway for neural and vascular communication between these structures.

Anatomical Definition and Structure

The infundibulum, also known as the pituitary stalk, is a key component of the neuroendocrine system with several important anatomical features:

• It forms a direct connection between the hypothalamus and the pituitary gland
• Contains the infundibular recess, which is a cerebrospinal fluid-filled canal that passes through the center of the pituitary stalk 1
• Extends from the floor of the third ventricle to the pituitary gland 2
• In 81% of individuals, the infundibular recess passes through the entire length of the pituitary stalk and reaches the upper surface of the pituitary gland 1

Embryological Development

The infundibulum has distinct developmental origins:

• It forms from the infundibulum, a ventral extension of the diencephalon during embryonic development 2
• This structure ultimately forms the posterior lobe of the pituitary gland (neurohypophysis) 2
• The anterior and intermediate lobes develop separately from Rathke's pouch (a dorsal evagination of the stomodeum) 2

Functional Significance

The infundibulum serves several critical physiological functions:

1. Neuronal pathway: It contains axons from neurons in the hypothalamus (specifically the supraoptic and paraventricular nuclei) that transport oxytocin and vasopressin to the posterior pituitary for release 2

2. Portal vascular system: Contains blood vessels that carry hypothalamic regulatory hormones to the anterior pituitary, controlling the release of:

   • Thyroid stimulating hormone
   • Corticotropin
   • Luteinizing hormone
   • Follicle stimulating hormone
   • Growth hormone
   • Prolactin 2

3. Cerebrospinal fluid communication: The infundibular recess may function in conjunction with the pituitary gland in cerebrospinal fluid dynamics 1

Clinical Relevance and Pathology

The infundibulum can be affected by various pathological conditions that fall into three main categories 3:

1. Congenital and developmental abnormalities

   • Pituitary stalk interruption syndrome
   • Ectopic posterior pituitary

2. Inflammatory and infectious conditions

   • Lymphocytic infundibulo-neurohypophysitis, which commonly presents as central diabetes insipidus 4

3. Neoplastic lesions

   • Primary tumors (rare)
   • Metastatic disease
   • Ganglion cell tumors (extremely rare) 5

Imaging Evaluation

MRI is the preferred imaging modality for evaluating the infundibulum:

• High-resolution pituitary protocols with focused field-of-view sequences are optimal for assessment 6
• T1 and T2-weighted sequences before and after contrast administration provide comprehensive evaluation 6
• The normal infundibulum appears as a styloid- or cone-shaped structure with variable inclinations toward the third ventricle floor 1
• CT is less sensitive compared to MRI for pituitary pathology, even with optimized technique 6

Clinical Implications

Lesions affecting the infundibulum can have significant clinical consequences:

• Disruption of posterior pituitary function can lead to diabetes insipidus
• Interference with the portal vascular system can affect anterior pituitary hormone production
• Mass lesions can cause compression of adjacent structures including the optic chiasm

When evaluating infundibular lesions, it's important to consider the patient's age, as the spectrum of pathology differs between pediatric and adult populations 3.