POSTPARTUM PITUITARY INFARCTION (SHEEHAN SYNDROME)

Overview and Pathophysiology

• Definition: Sheehan syndrome is postpartum necrosis of the pituitary gland secondary to severe blood loss and hypovolemia during or after childbirth.
• Mechanism:
  1. Pituitary Enlargement in Pregnancy: Primarily due to hyperplasia of lactotroph cells.
  2. Vulnerability to Blood Pressure Changes: The pituitary relies heavily on its portal venous system (relatively low-pressure).
  3. Ischemic Infarction:
     • Historically described as vasospasm of infundibular arteries drained by the portal system.
     • May also involve thrombosis or vascular compression, leading to infarction of the adenohypophysis.
  4. Infarcted Areas: Undergo necrosis, eventually replaced by fibrotic scar tissue.

Extent of Infarction

• Typical Involvement:
  • Often ~97% of the anterior lobe is affected, but the pars tuberalis and part of the superior surface may be spared.
  • Alternatively, a small region at the lateral pole or a thin peripheral rim of tissue adjacent to the sellar wall might remain viable, nourished by a separate capsular blood supply.
• Functional Threshold:
  • >75% loss of adenohypophyseal cells → partial pituitary failure.
  • >90% loss → complete pituitary failure.
  • >30% preserved → may prevent immediate severe hypopituitarism.

Clinical Presentation

1. Acute Onset
   • Severe hypovolemic shock (from hemorrhage) compounded by acute glucocorticoid deficiency can be life-threatening.
   • Immediate pituitary failure symptoms (e.g., shock, adrenal insufficiency).
2. Gradual Onset
   • Inability to lactate (due to prolactin deficiency) is often the first recognized sign postpartum.
   • Amenorrhea or oligomenorrhea, loss of axillary/pubic hair.
   • Lethargy, anorexia, weight loss, and other signs of anterior pituitary hormone deficiencies (TSH, ACTH, LH/FSH, GH).
   • Diabetes insipidus (posterior pituitary failure) is rare.

Diagnosis

• Clinical Suspicion:
  • History of severe postpartum hemorrhage requiring transfusion.
  • Postpartum failure to lactate, persistent amenorrhea, or secondary sexual hair loss.
• Laboratory Tests:
  • Morning (8 AM) Cortisol
  • Free Thyroxine (T4)
  • Prolactin (often low in Sheehan syndrome)
  • Estradiol
  • Insulinlike Growth Factor 1 (IGF-1)
• Imaging (MRI):
  • Early stages: Enlarged pituitary with ischemic infarct.
  • Over months: Gradual shrinkage → atrophy → “empty sella” appearance.

Treatment and Prognosis

• Lifelong Target Gland Hormone Replacement:
  1. Glucocorticoids (for ACTH deficiency)
  2. Levothyroxine (for TSH deficiency)
  3. Sex steroids (for LH/FSH deficiency) if fertility is not immediately desired; gonadotropins for fertility.
  4. GH replacement if needed (particularly in children or if adult GH deficiency is symptomatic).
• Acute Management: Prompt recognition and treatment of adrenal insufficiency is critical to prevent fatal adrenal crisis.
• Long-Term Outlook: With appropriate hormone replacement, patients can maintain a good quality of life.