Endocrine

Thyroid nodules/cancers, parathyroid, adrenal tumors, pituitary, and MEN syndromes for the Surgery Shelf.

Sources: extracted/theory-endocrine.md (TPOT-Surgery_Endocrine_GI.pdf, pp.57–88); First Aid 2026 (first-aid-usmle-bible).

High-Yield Points

• Solitary thyroid nodule: check TSH first → if normal/high, FNA; if low, radionuclide scan for a "hot" (rarely malignant) nodule. Prior neck irradiation sharply raises cancer risk.
• Papillary carcinoma (most common, ~85%): psammoma bodies, Orphan Annie nuclei, lymphatic spread, excellent prognosis. Follicular: FNA cannot diagnose (needs capsular/vascular invasion on resection), hematogenous spread. Medullary (MTC): parafollicular C cells, calcitonin + amyloid, part of MEN2 — screen/resect pheo first. Anaplastic: elderly, rapidly fixed/invasive, always stage IV, dismal.
• Graves: TSH-receptor-stimulating antibodies (TSI), diffuse goiter + proptosis, undetectable TSH. Thyroid storm (post-op/stress) → β-blocker + antithyroid drug + iodine after the antithyroid drug + steroids.
• Primary hyperparathyroidism: ↑Ca, ↓phosphate, ↑PTH — usually a single adenoma → excise it; 4-gland hyperplasia → subtotal (3.5-gland) or total parathyroidectomy + autotransplant.
• Pheochromocytoma: episodic HTN/headache/diaphoresis, ↑metanephrines; α-blockade (phenoxybenzamine) + volume BEFORE β-blockade; "10% rule."
• Primary hyperaldosteronism (Conn): HTN + hypokalemia + metabolic alkalosis + ↑aldosterone with low renin (↑aldo:renin) → unilateral adenoma cured by adrenalectomy.
• Cushing: confirm with overnight 1-mg dexamethasone + 24-h urinary free cortisol; then ACTH + high-dose dex localizes (pituitary suppresses & ↑ACTH; adrenal = ↓ACTH; ectopic = ↑ACTH, non-suppressible).
• Adrenal incidentaloma: exclude pheo before any biopsy; resect if functional or ≥5 cm, else observe.
• Insulinoma: Whipple triad + ↑insulin AND ↑C-peptide, negative sulfonylurea screen (exogenous insulin = low C-peptide). Prolactinoma (most common pituitary tumor) → dopamine agonist first-line even for macroadenoma.

Key Tables / Differentials

Thyroid cancers

MEN syndromes

Board Pearls

• High Ca + low phosphate + high PTH = primary hyperparathyroidism (single adenoma).
• Whenever pheo coexists (MEN2), resect the pheo first to avoid intraoperative hypertensive crisis.
• β-blocker before α-blocker in pheo → unopposed α → hypertensive crisis (never do it).
• MTC does not take up radioiodine; calcitonin is its tumor marker.
• Bilateral milky discharge + amenorrhea → check prolactin → prolactinoma → dopamine agonist.

Classic Vignette Triggers

• "Thyroid nodule + prior childhood neck radiation" → FNA (high cancer risk).
• "Hard, rapidly enlarging fixed neck mass + hoarseness in an elderly patient" → anaplastic carcinoma.
• "HTN + spontaneous hypokalemia + metabolic alkalosis" → Conn (low renin, high aldosterone).
• "Spells of headache, palpitations, sweating + paroxysmal HTN" → pheochromocytoma → α- then β-block, resect.
• "Refractory ulcers + diarrhea + hypercalcemia" → gastrinoma in MEN1.
• "Fasting confusion relieved by eating, ↑insulin + ↑C-peptide" → insulinoma.