📚 Endocrinology — L3: Pituitary Tumors

📚 Lecture Overview

This lecture covers the classification, clinical presentation, diagnostic evaluation, and management strategies for pituitary tumors, focusing specifically on prolactinomas and acromegaly. Understanding these neuroendocrine tumors is critical for clinicians to diagnose endocrine hypersecretion syndromes early, prevent permanent neuro-ophthalmologic damage, and manage systemic complications effectively.

🎯 Key Concepts & Definitions

• Microadenomas: Pituitary tumors measuring less than 10 mm in maximum diameter.
• Macroadenomas: Pituitary tumors measuring between 10 mm and 40 mm in diameter.
• Giant Adenomas: Pituitary tumors measuring greater than 40 mm in diameter.
• PIT-NET: Pituitary Neuro-Endocrine Tumors, the 2017 WHO term replacing "Pituitary Adenoma," classified using pituitary transcription factors.
• Apoplexy: Spontaneous hemorrhage or necrosis within a pituitary adenoma, often presenting with sudden, severe headache and cranial nerve palsy.
• Acromegaly: A slowly progressive disease caused by excess growth hormone (GH) and IGF-1 after epiphyseal plate closure.
• Gigantism: GH excess occurring before the closure of growth plates during puberty, leading to increased linear growth.

📖 Main Content

1. Classification of Pituitary Tumors

• Size Classification: Divided into microadenomas (<10 mm), macroadenomas (10–40 mm), and giant adenomas (>40 mm).
• Clinical/Immunohistochemical Distribution:
• Prolactinoma: Most common functional tumor (~51%).
• Non-functioning adenomas: ~37% of cases.
• Acromegaly (GH): ~8.5% (with ~15% GH content on immunohistochemistry).
• Cushing disease (ACTH): ~3% (~15% ACTH content).
• Biological Behavior & Invasiveness:
• Invasive adenomas: Invade the sphenoid or cavernous sinus in up to 40% of cases, increasing recurrence/regrowth risk to 25%–50%.
• Aggressive adenomas: Comprise 2% of macroadenomas; characterized by rapid growth ($≥$20% increase in longest diameter in <6–12 months).
• Carcinomas: Extremely rare (0.1%–0.4%), defined by cranio-spinal or systemic metastasis.
• Surgical Classifications:
• Hardy classification: Differentiates noninvasive intrasellar tumors from invasive tumors causing bone destruction.
• Knosp classification: Grades cavernous sinus involvement using the parasellar internal carotid artery as a landmark to predict surgical resection success.
• 2017 WHO Pathological Classification: Uses transcription factors like PIT1 (mammosomatotrophs, somatotrophs, lactotrophs, thyrotrophs), TPIT (corticotrophs), and SF1 (gonadotrophs).

2. Prolactinomas

• Epidemiology: Most frequent functional pituitary tumor. Female-to-male ratio is 5:1 to 10:1 in reproductive years (ages 25–44), equalizing postmenopause. Microprolactinomas predominate in women, whereas macroprolactinomas are more common in men (4:1 ratio).
• Clinical Presentation:
• Women of reproductive age: Oligo-amenorrhea or short luteal phase (85–90%), anovulatory infertility, and spontaneous or provoked galactorrhea (~90%).
• Postmenopausal women: Mass effect symptoms.
• Men: Half present with tumor mass effects (visual impairment, headache) and half with hypogonadism symptoms (loss of libido, erectile dysfunction, infertility).
• Diagnostic Evaluation & Caveats:
• Serum PRL levels >200–250 ng/mL are almost always due to a macroprolactinoma.
• Stress (e.g., venipuncture) can falsely elevate PRL 2- to 4-fold; use cannulated sampling if suspected.
• Exclude non-tumoral causes: medications, primary hypothyroidism, renal insufficiency, liver failure, and pregnancy.
• Dynamic gadolinium-based MRI is essential for initial diagnosis and treatment response monitoring.
• Complications & Screening:
• Evaluate for bone disease via baseline DXA if long-standing hypogonadism (>6 months) or osteoporosis risk factors exist.
• Screen for GH, TSH, and ACTH deficiencies in all macroadenomas and microadenomas 6–9 mm in size. Measure IGF-I to rule out mixed GH/PRL hypersecretion.
• Treatment & Management:
• Dopamine agonists (DAs), specifically cabergoline, are first-line therapy regardless of tumor size or symptom severity due to high efficacy and long half-life.
• Normalizes PRL in ~90% of microprolactinomas and 75–80% of macroprolactinomas.
• Cabergoline Adverse Effects: GI symptoms, dizziness, fatigue, and rare impulse control disorders (compulsive buying, gambling, hypersexuality). Perform baseline/periodic echocardiography if using high doses (>2.0 mg/week) to monitor for valve alterations.
• Surgical and Radiologic Options: Surgery is reserved for rapid vision loss, apoplexy, CSF rhinorrhoea, or DA resistance/intolerance. Radiotherapy is a third-line option for non-resectable or poorly responsive remnants.

3. Acromegaly

• Pathophysiology: A slowly progressive disease caused by excess growth hormone (GH) and downstream insulin-like growth factor I (IGF-1). Gigantism occurs before epiphyseal fusion; acromegaly occurs after epiphyseal closure.
• Etiology: ~99% caused by GH-secreting pituitary adenomas (over 70% are macroadenomas at presentation). Rarely caused by ectopic GHRH or GH secretion.
• Clinical Manifestations:
• Facial/Acral Dysmorphia: Wide hands/feet, broad stubby fingers, rectangular face, widened nose, prominent cheekbones, bulging forehead, and prognathism (jaw malocclusion/teeth separation).
• Systemic Comorbidities: Diabetes or glucose intolerance (20–56%), hypertension (20–50%), obstructive sleep apnea (OSAS) (60–80%), left ventricular hypertrophy, and colonic polyps (up to 45%).
• Laboratory Diagnosis:
• Elevated serum IGF-1 (age- and sex-adjusted) combined with a lack of GH suppression (<1 µg/L or <0.4 µg/L on ultrasensitive assays) following a 75 g oral glucose tolerance test (OGTT).
• Paradoxical GH response: 25–30% of patients show increased GH after glucose load due to aberrant GIP receptor signaling.
• Management & Treatment Goals:
• Primary goal: Normalize age-adjusted IGF-1 and reduce GH to <1 ng/mL (or <0.4 ng/mL with modern assays).
• Surgical Resection: First-line approach for most patients via endoscopic or microscopic transsphenoidal surgery; yields remission in 75–90% of microadenomas and 40–60% of macroadenomas.
• Medical Therapy:
  • First-generation somatostatin receptor ligands (SRLs) (octreotide LAR, lanreotide autogel) are first-line medical therapy for persistent disease.
  • Second-line options include cabergoline, the GH receptor antagonist pegvisomant (PEG), and second-generation SRL pasireotide (PAS).
• Radiotherapy: Reserved as a third-line option for non-resectable or treatment-refractory tumors.

📊 Visual Learning

💡 Important Points to Remember

• Prolactin Threshold: Serum prolactin levels $>200--250 ng/mL$ almost always indicate a macroprolactinoma.
• Cabergoline First-Line: Cabergoline is the preferred dopamine agonist due to its long half-life and high efficacy in shrinking prolactinomas.
• DA Side Effects: Watch for rare impulse control disorders and perform baseline/serial echocardiograms if using high-dose cabergoline ($>2.0 mg/week$).
• Acromegaly Diagnosis: Confirmed by elevated IGF-1 and failure of GH to suppress below $<1 \mug/L$ (or $<0.4 ng/mL$ with ultrasensitive assays) during an OGTT.
• Acromegaly Comorbidities: Systemic effects include hypertension, sleep apnea (OSAS), diabetes/glucose intolerance, cardiomyopathy, and colonic polyps.
• Surgical Remission Rates: Transsphenoidal surgery cures 75–90% of microadenomas and 40–60% of macroadenomas for acromegaly.
• Mixed Tumors: GH/PRL co-secreting adenomas have significantly lower surgical remission rates (20% vs. 68%) compared to pure GH-secreting tumors.
• WHO 2017 Update: Pituitary adenomas are now termed PIT-NETs, categorized using pituitary transcription factors (PIT1, TPIT, SF1).
• Invasive vs. Aggressive: Up to 40% of adenomas are invasive into the cavernous/sphenoid sinuses, while aggressive tumors show a $≥ 20%$ size increase in $<6--12$ months.
• Common Exam Trap: Failing to recognize that stress, renal failure, liver disease, or medications (like antipsychotics) can cause mild hyperprolactinemia, which mimics a prolactinoma.

⚠️ Common Exam Questions

• MCQ Trick: Examiners often present a patient with mild hyperprolactinemia ($<5×$ upper limit of normal) and immediate MRI findings. The trap is jumping straight to a tumor diagnosis when the correct initial step is repeating the test or reviewing medication history and stress factors.
• Diagnostic Pathway Trap: In acromegaly questions, random single GH measurements are useless due to pulsatile secretion. Examiners will try to trick students into diagnosing acromegaly based on a single high random GH level instead of requiring an elevated IGF-1 and failure of GH suppression on an OGTT.
• Treatment Choice: Questions frequently test first-line interventions. Remember: cabergoline is first-line for prolactinomas (regardless of size), while surgery is first-line for acromegaly, followed by first-generation SRLs if disease persists.

📦 Quick Review Checklist

I can differentiate microadenomas, macroadenomas, and giant adenomas by size
I understand the 2017 WHO PIT-NET classification using transcription factors (PIT1, TPIT, SF1)
I can list the classic clinical presentations of prolactinomas in women vs. men
I know why serum prolactin levels above 250 ng/mL point directly to a macroprolactinoma
I understand the diagnostic criteria for acromegaly (elevated IGF-1 and failed GH suppression on OGTT)
I can identify key systemic comorbidities of acromegaly (OSAS, diabetes, hypertension, colonic polyps)
I know why cabergoline is preferred over other dopamine agonists
I understand the indications for transsphenoidal surgery vs. medical therapy vs. radiotherapy