Introduction

The pituitary stalk, also called the infundibulum, is a narrow funnel of tissue that links the hypothalamus to the pituitary gland. It carries small blood vessels and axons that transport hypothalamic releasing factors and posterior pituitary hormones. This link ensures that hypothalamic signals reach the pituitary and that pituitary hormones are secreted in a regulated way. Any damage or abnormality of the pituitary stalk hormone flow and lead to endocrine dysfunction.

Empty Sella Syndrome (ESS) is a radiological condition in which the sella turcica is partly or completely filled with cerebrospinal fluid (CSF), leading to a flattened or shrunken pituitary gland. Because the pituitary stalk crosses the sella to reach the gland, changes in the sellar space can alter its shape and function. Understanding pituitary stalk abnormalities is therefore important for interpreting the clinical significance of ESS.

Anatomy of the pituitary stalk

The pituitary stalk measures about 3–5 mm in length and 2–3 mm in diameter in adults. It tapers smoothly from the hypothalamus down to the pituitary. Through the stalk run two important pathways: the portal venous system, which carries hypothalamic releasing hormones to the anterior pituitary, and the axons of hypothalamic neurons, which carry precursors of vasopressin and oxytocin to the posterior pituitary. Due to this anatomy, the stalk is crucial for both anterior and posterior pituitary function.

Empty sella syndrome

Definition

An empty sella is seen on MRI when the sella turcica contains CSF and the pituitary is thinned.

• Partial empty sella: less than 50% of the sella volume is filled with CSF
• Complete empty sella: more than 50% of the sella is CSF-filled, and the gland is ≤2 mm thick

Types

• Primary ESS: occurs without prior pituitary disease. The most accepted explanation is a defect in the sellar diaphragm, which allows CSF to pulsate into the sella and flatten the gland
• Secondary ESS: occurs after pituitary damage, such as surgery, haemorrhage (Sheehan syndrome), trauma, irradiation, infection, or autoimmune destruction. In this case, the pituitary shrinks or disappears, leaving a space

Effect of empty sella on the pituitary stalk

As CSF fills the sella, the pituitary gland flattens against the floor, and the stalk is stretched upward. This mechanical stretching may reduce dopamine transport from the hypothalamus. Because dopamine normally inhibits prolactin release, disruption of this pathway can result in mild hyperprolactinemia. 

This “stalk effect” is one of the most consistent biochemical findings in ESS. MRI often shows the stalk elongated and centred in the midline, although in some cases it may be displaced or kinked.

Types of pituitary stalk abnormalities

Congenital abnormalities

Pituitary stalk interruption syndrome (PSIS)

PSIS is a developmental disorder in which the stalk is absent or very thin. MRI shows three key findings: a small anterior pituitary, an ectopic posterior pituitary located at the median eminence, and an invisible or interrupted stalk. These patients often present in childhood with short stature and growth hormone deficiency, but by adulthood, they may have multiple pituitary hormone deficits. The sella may appear partially empty because of the underdeveloped gland.

Septo-optic dysplasia (SOD)

SOD is another congenital syndrome involving midline structures. Patients have optic nerve hypoplasia, absence of the septum pellucidum, and pituitary dysfunction. MRI often shows a very thin or absent stalk, an ectopic posterior pituitary, and an empty or partially empty sella. Endocrine deficits are variable, but growth hormone and ACTH deficiencies are common.

Acquired abnormalities

Inflammatory and autoimmune causes

Inflammatory processes such as lymphocytic hypophysitis can cause diffuse stalk thickening. Patients often present with headache, visual symptoms, or hypopituitarism. Diabetes insipidus is common because the posterior pituitary pathway is disrupted. Over time, chronic inflammation can lead to pituitary shrinkage and a secondary empty sella. Other infiltrative disorders, such as sarcoidosis and Langerhans cell histiocytosis, also cause stalk thickening and can progress to pituitary atrophy.

Tumours

Several tumours can arise in or around the pituitary stalk, including craniopharyngiomas, germinomas, and metastases. These masses often cause visible stalk enlargement on MRI and may compress both the stalk and the gland. Treatment with surgery or radiation may control the tumour but often damages the pituitary, leading to secondary ESS. Tumour-related stalk damage usually results in significant hormone deficiencies, including diabetes insipidus.

Imaging and diagnosis

MRI is the key tool to see both the empty sella and the stalk. In empty sella syndrome, T1-weighted MRI typically shows a fluid-filled sella with a thin pituitary rim and a slit of normal gland at the bottom. The pituitary stalk itself is often flattened or thinned by the CSF and lies in the midline. Primary ESS usually has a normal-appearing residual gland and stalk, whereas secondary ESS often shows distortion or scarring of the pituitary and stalk.  Pituitary stalk abnormalities are measured by size: a normal adult stalk is about 2–3 mm in diameter. Thickening is usually defined as ≥3–4 mm on MRI. In contrast, an interrupted or absent stalk may not be visible on MRI, except by inference (e.g. an ectopic posterior lobe).

If a pituitary stalk abnormality is seen, it should be correlated with clinical findings. Thickening suggests inflammation or tumour, whereas a barely visible stalk suggests PSIS or severe damage. In empty sella patients, any unusual stalk appearance should prompt further evaluation.  For example, a very thick stalk in an empty sella might indicate past hypophysitis or Langerhans cell disease. If the stalk is absent or ectopic, one should consider PSIS or other developmental syndromes. A stretched-but-normal stalk in an otherwise asymptomatic patient often requires no specific treatment, but the clinician must check for hormone changes (especially prolactin or GH levels).

Hormonal significance

Pituitary stalk abnormalities greatly influence pituitary function. In PSIS, the lack of a stalk means the hypothalamic hormone supply is cut off.  These patients typically have panhypopituitarism (multiple pituitary hormone failures) and often require lifelong hormone replacement. Even without full PSIS, any disruption of the stalk impairs pituitary trophic regulation. Pituitary inflammation or tumour that damages the stalk often leads to central diabetes insipidus (ADH deficiency) and multiple pituitary hormone deficits.

In empty sella syndrome, hormone effects are more subtle but still important. Many patients have normal pituitary function, especially in mild ESS. However, up to one-third of patients may have one or more hormone deficiencies. The most common issue is mild hyperprolactinemia, likely due to stalk compression as noted. Low growth hormone and low gonadotropins are also reported. Clinicians should screen ESS patients for endocrine problems even if the finding was incidental. A detailed pituitary hormone panel (ACTH/cortisol, TSH/FT4, GH/IGF-1, LH/FSH, prolactin) and a diabetes insipidus evaluation are recommended when ESS is discovered. In our earlier discussion of ESS, we noted that multiple studies find pituitary deficiency in a substantial fraction of ESS cases, especially in men and in secondary ESS.

Summary

Pituitary stalk abnormalities can play a key role in empty sella syndrome.  Certain congenital or acquired stalk lesions actually cause the pituitary to shrink and leave an empty sella (as in PSIS or chronic hypophysitis).  Conversely, an empty sella itself mechanically stretches the stalk, which can alter its function (e.g. reducing dopamine delivery and raising prolactin). Thus, the stalk’s status helps determine the clinical picture: an absent or thick stalk usually indicates a pathological process requiring further workup, whereas an elongated but otherwise normal stalk often reflects a benign primary empty sella.  

In all cases, careful MRI evaluation of the stalk and pituitary plus endocrine testing is important. When empty sella and stalk issues coincide, patients should be managed with a multidisciplinary approach (endocrinology, neurology/neurosurgery, ophthalmology), treating any hormone deficits and monitoring for evolving symptoms.