单选题 A 20-year-old woman comes to the physician because of multiple burns on her hands. She says that she gets burned quite often when she cooks, particularly while operating the oven. She also has burned herself when picking up her morning cup of coffee and when testing the water temperature in the shower. The patient is concerned because she cannot feel when objects are "really hot" and often does not notice that she has burns until she looks at her hands. She has no significant past medical history, no recent illnesses, and no sick contacts. Her surgical history is significant only for removal of impacted wisdom teeth 1 year ago. The patient has never smoked, drinks alcohol occasionally, and does not use illicit drugs. Her family history is significant for multiple sclerosis in her mother. Examination shows diminished pinprick and temperature sensation across the upper back, shoulders, and arms bilaterally. Light touch, position, and vibration sense are preserved. Examination of the lower extremities is unremarkable. Damage to which of the following spinal cord areas is most likely responsible for this patient's symptoms?

单选题 A 26-year-old man is brought to the emergency department after a high-speed motorcycle collision.  The patient was thrown several feet after his motorcycle collided with a car.  On arrival, he is profoundly comatose.  A CT scan of the head performed within an hour of the event shows no abnormalities.  The patient dies several hours later, and autopsy examination is performed.  Brain histopathology shows widespread axonal swelling, predominantly at the gray-white junction.  Immunohistochemical staining of these axons reveals accumulation of alpha-synuclein and amyloid precursor proteins.  Which of the following is the most likely cause of these observed findings?

单选题 A 65-year-old woman is found dead in her house.  The family notes that she had difficulty walking over the past few months.  The woman had a history of atrial fibrillation treated with anticoagulation therapy.  Autopsy reveals bruising of the scalp.  Intracranially, there is a large epidural hemorrhage with brain herniation.  In addition, the spinal cord shows symmetric myelin layer vacuolization and axonal degeneration involving the posterior columns and the lateral corticospinal tracts.  Which of the following is the most likely cause of this woman's spinal cord findings?

单选题 A 1-month-old, full-term boy is brought to the emergency department by his mother due to difficulty awakening him from sleep.  The mother says that the infant was momentarily left alone this morning and rolled off a bed.  Since then, he has been sleepy and less active than usual.  Physical examination shows a lethargic boy with a large, full anterior fontanelle.  Bilateral retinal hemorrhages are seen on funduscopic examination.  Which of the following is the most likely diagnosis?

单选题 A 62-year-old man is brought to the emergency department after a generalized tonic-clonic seizure.  His wife reports that he has been having episodic headaches, nausea, and progressive weakness for the past several weeks.  The headaches are particularly worse at night and occasionally awaken him.  Other medical conditions include well-controlled hypertension and osteoarthritis.  On physical examination, the patient is postictal but follows simple commands.  He is admitted to the hospital for further evaluation but dies several days later due to aspiration pneumonia and septic shock.  During autopsy, examination of the brain shows a poorly circumscribed, hemorrhagic, necrotic mass in the left cerebral hemisphere with a midline shift away from the mass.  Which of the following is the most likely diagnosis?

单选题 A 16-year-old boy is being evaluated for difficulty walking.  On physical examination, he has thoracic scoliosis and multiple small scars on his hands.  When asked about these, the boy replies, "I frequently burn my hands by accident because I can't feel the heat."  Neurologic examination reveals 1+ biceps reflexes and 3+ patellar reflexes bilaterally, as well as decreased muscle strength in the bilateral upper and lower extremities.  His hand muscles are atrophic, and position and vibration senses in the feet are also impaired.  Which of the following is the most likely cause of this patient's problems?

单选题 A 78-year-old female is brought to the ER because of altered mental status of recent onset and difficulty walking. She has a history of Parkinsonism and has had difficulty walking lately. She lives alone and has had a few falls recently. Her BP is 180/100 mm Hg and pulse is 68/min. Her CT scan of the head is shown below. Which of the following is the most likely cause of her symptoms?

单选题 A 45-year-old man is brought to the emergency department after sustaining a traumatic head injury in a motor vehicle collision. The patient was found unresponsive and had several generalized tonic-clonic seizures during transport. Medical history includes hypertension as well as alcohol and cocaine misuse. Temperature is 36.7 C (98.1 F), blood pressure is 170/96 mm Hg, pulse is 50/min, and respirations are 10/min. Pulse oximetry shows 98% on mechanical ventilation with 50% oxygen. On examination, the patient is comatose with midpositioned and fixed pupils and rigid extension of the upper and lower extremities. Noncontrast CT scan of the head is shown in the image below: Damage to which of the following structures is the most likely explanation for this patient's abnormal posturing?

单选题 A 64-year-old man is being evaluated for nausea and a new-onset headache that worsens when he bends over. Brain imaging shows a hemispheric cerebral mass that is subsequently biopsied. Light microscopy of the tissue specimen is shown in the image below. Which of the following histologic findings is most characteristic of this lesion?