A 58-year-old woman presents to the clinic with an abnormal sensation on the left side of her body that has been present for the past several months. At first, the area seemed numb and she recalls touching a hot stove and accidentally burning herself but not feeling the heat. Now she is suffering from a constant, uncomfortable burning pain on her left side for the past week. The pain gets worse when someone even lightly touches that side. She has recently immigrated and her past medical records are unavailable. Last month she had a stroke but she cannot recall any details from the event. She confirms a history of hypertension, type II diabetes mellitus, and bilateral knee pain. She also had cardiac surgery 20 years ago. She denies fever, mood changes, weight changes, and trauma to the head, neck, or limbs. Her blood pressure is 162/90 mm Hg, the heart rate is 82/min, and the respiratory rate is 15/min. Multiple old burn marks are visible on the left hand and forearm. Muscle strength is mildly reduced in the left upper and lower limbs. Hyperesthesia is noted in the left upper and lower limbs. Laboratory results are significant for: Hemoglobin 13.9 g/dL MCV 92 fL White blood cells 7,500/mm3 Platelets 278,000/mm3 Creatinine 1.3 U/L BUN 38 mg/dL TSH 2.5 uU/L Hemoglobin A1c 7.9% Vitamin B12 526 ng/L What is the most likely diagnosis?

Subacute combined degeneration of spinal cord

A 80-year-old man is brought to the emergency department with complaints that he "can't control his left leg". His symptoms started a few hours ago. He was outside taking a walk with his wife when suddenly his leg shot out and kicked her. His past medical history is notable for diabetes, hypertension, and a myocardial infarction 5 years ago. He smokes 1-2 cigarettes/day. He does not use alcohol or illicit drugs. On exam, the patient has intermittent wide, flinging movements that affect his proximal left arm and left leg. Which of the following parts of his brain is most likely damaged?

Ventral posterior thalamic nucleus

A 61-year-old man is brought to the emergency department because of increasing weakness of his right arm and leg that began when he woke up that morning. He did not notice any weakness when he went to bed the night before. He has hypertension and hypercholesterolemia. Current medications include hydrochlorothiazide and atorvastatin. He is alert and oriented to person, time, place. His temperature is 36.7°C (98°F), pulse is 91/min, and blood pressure is 132/84 mm Hg. Examination shows drooping of the right side of the face. Muscle strength is decreased in the right upper and lower extremities. Deep tendon reflexes are 4+ on the right side. Sensation is intact. His speech is normal in rate and rhythm. The remainder of the examination shows no abnormalities. An infarction of which of the following sites is the most likely cause of this patient's symptoms?

Posterior limb of the left internal capsule

Thalamus and hypothalamus for USMLE Step 3: High-Yield Anatomy Lessons

Thalamus - Grand Central Station

Major relay for all ascending sensory information (except olfaction) to the cortex.
Key Nuclei & Functions:
- VPL (Ventral Posterolateral): Sensation from the body.
  - Input: Spinothalamic tract, dorsal columns/medial lemniscus.
- VPM (Ventral Posteromedial): Sensation from the face.
  - Input: Trigeminal pathway.
  - 📌 Makeup on the face (VPM).
- LGN (Lateral Geniculate Nucleus): Vision.
  - Input: Optic tract (CN II).
  - 📌 Light for LGN.
- MGN (Medial Geniculate Nucleus): Hearing.
  - Input: Brachium of the inferior colliculus.
  - 📌 Music for MGN.
- VL (Ventral Lateral): Motor feedback.
  - Input: Cerebellum, basal ganglia.

⭐ Thalamic Syndrome (Dejerine-Roussy): A stroke (often PCA territory) can cause contralateral sensory loss, which may be followed weeks later by severe, chronic neuropathic pain (allodynia).

Hypothalamus - The Body's CEO

Regulates vital functions via neural and endocrine signals. 📌 Mnemonic: TAN HATS

Thirst & water balance (Supraoptic/PVN → ADH)
Adenohypophysis (anterior pituitary) control
Neurohypophysis (posterior pituitary) release of hormones
Hunger & satiety
Autonomic nervous system regulation
Temperature regulation
Sexual functions & sleep-wake cycle

Sagittal view of hypothalamus with major nuclei

Key Nuclei & Functions:

Lateral: Hunger. Injury → lean.
Ventromedial: Satiety. Injury → very massive.
Anterior: Cooling (parasympathetic). A/C unit.
Posterior: Heating (sympathetic). Hot pot.
Suprachiasmatic (SCN): Circadian rhythm.
Supraoptic & Paraventricular (PVN): Synthesize ADH and oxytocin.

⭐ Exam Favorite: Craniopharyngiomas, benign tumors arising from Rathke's pouch remnants, can compress the hypothalamus, leading to endocrine dysfunction (e.g., diabetes insipidus), visual field defects, and headaches.

Vascular & Clinical - When Circuits Break

Thalamic Strokes (Posterior Circulation)
- Dejerine-Roussy Syndrome: PCA territory infarct. Presents with contralateral hemisensory loss, followed weeks later by severe, burning neuropathic pain (thalamic pain).
- VPL/VPM Nuclei Infarct: Pure sensory stroke. Contralateral loss of all sensation (face and body).
- VA/VL Nuclei Infarct: Can cause movement disorders like ataxia or abulia (impaired initiative).
Hypothalamic Syndromes
- Wernicke-Korsakoff Syndrome: Damage to mammillary bodies from thiamine (B1) deficiency. Triad: ataxia, ophthalmoplegia, confusion.
- Craniopharyngioma: Suprasellar tumor compressing the hypothalamus, leading to endocrine dysfunction (e.g., ↓GH, DI) and visual field defects.

Arterial supply of the thalamus and surrounding structures

⭐ Thalamic Pain (Central Post-Stroke Pain): A paradoxical, delayed-onset burning pain and allodynia in the area of sensory loss following a thalamic stroke. It is notoriously difficult to treat.

High‑Yield Points - ⚡ Biggest Takeaways

The thalamus is the critical relay station for all sensory information, except for olfaction.

The hypothalamus is the master regulator of homeostasis, controlling the autonomic nervous system and endocrine system.

Key thalamic nuclei include VPL/VPM (somatosensation), LGN (vision), and MGN (audition).

Key hypothalamic nuclei regulate circadian rhythms (SCN), hunger (lateral), and satiety (ventromedial).

A thalamic stroke classically presents with contralateral sensory loss across all modalities.

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Thalamus and hypothalamus