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Infundibulum

The infundibulum, also known as the pituitary stalk, is a slender midline structure connecting the hypothalamus to the pituitary gland. It serves as the critical anatomical and functional conduit for neural and hormonal communication between the hypothalamus and hypophysis, enabling regulation of endocrine homeostasis.

The infundibulum is of major importance in neuroendocrinology and neuroradiology, as subtle changes in its thickness, signal, or enhancement may indicate systemic, inflammatory, neoplastic, or infiltrative disease.

Synonyms

  • Pituitary stalk

  • Infundibular stalk

Location

  • Midline structure within the suprasellar cistern

  • Extends from the tuber cinereum of the hypothalamus superiorly

  • Inserts into the posterior aspect of the pituitary gland inferiorly

  • Traverses the diaphragma sellae

  • Situated posterior to the optic chiasm

  • Anterior to the mammillary bodies

  • Superior to the pituitary gland within the sella turcica

Anatomical components

  • Neural component:

    • Hypothalamo-hypophyseal tract

    • Axons from supraoptic and paraventricular nuclei

  • Vascular component:

    • Hypothalamo-hypophyseal portal venous system

  • Glial and connective tissue framework:

    • Provides structural support and compartmentalization

Relations

Anteriorly:

  • Optic chiasm

  • Optic nerves

Posteriorly:

  • Mammillary bodies

  • Posterior perforated substance

Superiorly:

  • Hypothalamus

  • Third ventricle floor

Inferiorly:

  • Pituitary gland (neurohypophysis)

Laterally:

  • Suprasellar cistern

  • Cavernous sinuses (indirectly)

Vessels and connections

  • Superior hypophyseal arteries:

    • Supply the upper infundibulum and median eminence

  • Inferior hypophyseal arteries:

    • Supply the lower stalk and posterior pituitary

  • Portal venous system:

    • Transports releasing and inhibiting hormones to anterior pituitary

Function

  • Neuroendocrine communication: Conveys hypothalamic hormones to the pituitary gland

  • Hormone transport: Allows oxytocin and vasopressin transport to posterior pituitary

  • Endocrine regulation: Essential for control of growth, thyroid, adrenal, gonadal, and water balance functions

  • Integration: Links central nervous system with endocrine system

Clinical significance

  • Infundibular thickening: Seen in sarcoidosis, Langerhans cell histiocytosis, tuberculosis, lymphoma, and hypophysitis

  • Diabetes insipidus: Damage or infiltration disrupts vasopressin transport

  • Tumors: Germinomas, craniopharyngiomas, metastases may involve the stalk

  • Congenital anomalies: Interrupted pituitary stalk syndrome

  • Post-surgical or post-radiation change: Stalk edema or scarring

  • Imaging pitfall: Mild symmetric thickening can be physiological, especially in children

MRI appearance

T1-weighted images:

  • Normal infundibulum: Thin, midline structure with intermediate signal intensity

  • Normal thickness:

    • ≤3 mm at the level of the median eminence

    • ≤2 mm at the level of the pituitary insertion

  • Posterior pituitary bright spot: Normally present inferior to the stalk

T2-weighted images:

  • Normal: Intermediate signal intensity

Diffusion-weighted imaging (DWI):

  • Normal: No diffusion restriction

Post-contrast T1-weighted images:

  • Normal: Mild, homogeneous enhancement

CT appearance

Non-contrast CT:

  • Normal infundibulum: Usually not well visualized

Post-contrast CT:

  • Normal: Thin enhancing stalk may be faintly seen

MRI images

MRI Infundibulum axial anatomy image -img-00000-00000

MRI images

MRI Infundibulum sag anatomy image -img-00000-00000

MRI images

MRI Infundibulumcoronal anatomy image -img-00000-00000