A 73-year-old man comes to the emergency department due to right-sided weakness and difficulty speaking.  The patient woke up with the symptoms an hour before arriving but felt well when he went to bed last night.  He has a history of paroxysmal atrial fibrillation but is not adherent with medical therapy.  Temperature is 98.6 F (37 C), blood pressure is 130/70 mm Hg, and pulse is 110/min and irregularly irregular.  Physical examination shows right-sided hemiplegia, hemisensory loss, and aphasia.  Despite appropriate treatment, the patient’s symptoms fail to improve.  Over the next week, which of the following processes is most likely to occur in the affected brain region?

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?

A 65-year-old woman is brought to the clinic by her husband due to worsening memory problems.  She has a medical history significant for long-standing hypertension, type 2 diabetes mellitus, and depression.  Physical examination shows cognitive impairment but no focal neurologic deficits.  Two years later, the patient dies suddenly from a massive myocardial infarction.  Congo red staining of brain samples obtained from the hippocampus and cerebral arterioles reveals patchy red deposits that turn yellow-green under polarized light.  This patient most likely suffered from which of the following conditions?

A 34-year-old woman comes to the office due to a 2-day history of reduced sensation in her legs.  Lately, the patient has also had significant fatigue, especially with exercise.  Six months ago, she had an episode of visual blurring that resolved spontaneously after a few days.  Medical history is significant for psoriasis, for which she uses a topical glucocorticoid ointment.  The patient does not use tobacco or illicit drugs.  Vital signs are normal.  Examination indicates decreased pain and light touch perception in both legs below the level of the umbilicus.  Mild bilateral spasticity is noted.  Which of the following pathologic brain lesions is most specific for this patient’s disease process?

A 59-year-old man comes to the emergency department with diplopia that started several hours ago.  His past medical history is significant for long-standing diabetes with poor glycemic control, right-knee osteoarthritis, and peptic ulcer disease.  Physical examination shows right-sided ptosis with the right pupil in the inferolateral position.  Pupils are equal in size and reactive to light bilaterally.  This patient’s condition is most likely due to which of the following etiologies?

A 45-year-old woman is brought to the emergency department after an episode during which she abruptly lost consciousness and had rhythmic jerking movements of the limbs followed by a period of confusion.  The patient has had mild daily headaches associated with nausea that have progressed over the past 2 years.  The headaches are worse at night and occasionally awaken her.  The patient reports no head trauma, visual changes, weakness, numbness, or difficulty swallowing or speaking.  She does not use alcohol or illicit drugs.  There is no family history of seizures.  An intracranial mass is discovered on neuroimaging and a biopsy of the mass is shown in the image below.

Which of the following is the most likely diagnosis?

A 62-year-old woman comes to the office due to tingling and numbness in her feet over the last several months.  The patient has also noticed a small ulcer on her right foot that “doesn’t seem to be healing.”  Medical history is significant for long-term diabetes, hypertension, and gout.  Physical examination shows decreased pain sensation over both feet and bilateral absence of ankle reflexes.  This patient’s neurological symptoms are most likely associated with which of the following features?

A 56-year-old man is brought to the emergency department due to progressive weakness and lethargy.  The patient has also had a nonproductive cough for the past several weeks.  He has no prior medical conditions and takes no medications.  He has smoked a pack of cigarettes daily for 30 years.  Physical examination shows no abnormalities.  Chest x-ray reveals a lung mass.  Further evaluation reveals an electrolyte abnormality induced by ectopic antidiuretic hormone production from a lung mass.  This patient is at greatest risk of which of the following conditions if his electrolyte abnormality is corrected too quickly?

A 23-year-old, previously healthy man was involved in a motor vehicle collision.  He lost consciousness at the scene but recovered by the time emergency medical services arrived.  The patient was alert and awake in the ambulance but lost consciousness again soon after arriving at the emergency department.  His breath smells of alcohol.  Blood pressure is 130/90 mm Hg, pulse is 68/min, and respirations are 12/min.  A bruise is noted over the left temple area.  The left pupil is mildly dilated.  Brain imaging would most likely reveal blood accumulating between which of the following tissues?

A researcher is studying neuronal changes in various physiologic and pathologic states.  Microscopic examination of neural tissue obtained from experimental animals reveals neurons with shrunken nuclei and eosinophilic cytoplasm lacking Nissl bodies.  Which of the following is the most likely cause of these findings?

A 27-year-old woman comes to the office due to almost daily headaches for the past 3 months.  The patient describes constant “dull pressure” in her head that is worse at the end of the day.  She is an office manager and is able to work through the pain.  The patient has a history of seasonal allergies and her sister has migraine headaches.  Which of the following is the most likely diagnosis?

Experimental animals are immunized to protein fragments derived from peripheral nerve myelin.  Subsequent analysis finds evidence of a T-cell response as well as production of autoantibodies against nonprotein antigens.  This leads to segmental demyelination of peripheral nerves in the animals.  The experimentally induced condition is most analogous to which of the following?

A 24-year-old man comes to the office for hearing loss, tinnitus, and unsteadiness with walking.  A contrast-enhanced, T1-weighted image of his brain is shown below.

This patient is most likely to have a mutation involving which of the following genes?

A 70-year-old woman with a history of unilateral extremity weakness and seizures is found unresponsive at home by her home health care nurse.  On arrival of emergency medical services, she is found to have no pulse or spontaneous respirations and is declared dead.  Autopsy shows a large thrombus occluding the left anterior descending coronary artery.  Additional cerebral findings are shown in the exhibit.  Which of the following most accurately describes the pathogenesis of this patient’s brain lesion?

A 56-year-old man dies in the hospital due to aspiration-related complications.  The patient was admitted 5 days ago with right-sided weakness, sensory loss, and difficulty with speech and swallowing.  CT scan revealed an area of hypodensity in the left frontoparietal region.  Autopsy examination is performed, and a section of loose, spongy tissue from the abnormal brain area is obtained.  Histologic findings after staining for lipids are shown below.

The cells most intensely stained in this patient’s brain specimen represent which of the following cell types?

A 43-year-old woman is brought to the emergency department because of a sudden and severe headache.  Her blood pressure is 160/90 mm Hg and pulse is 90/min.  Her pupils are symmetric and reactive to light and she can move all four extremities without weakness.  CT of her head is shown below.

This patient’s condition is most likely caused by which of the following?

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?

A 72-year-old woman comes to the office for a routine follow-up visit accompanied by her son.  The patient has experienced progressive memory loss over the last 2 years.  She now needs help with her daily activities, such as shopping and housekeeping.  The patient’s son says, “She used to be such an independent person, but now she needs help with most things.  She even forgot my name the other day!”  Medical history includes hypertension, hyperlipidemia, and type 2 diabetes mellitus.  Family history includes major depressive disorder in her father.  MRI reveals diffuse cortical and hippocampal atrophy.  Which of the following biochemical changes is most likely contributing to this patient’s condition?

A 57-year-old man is hospitalized for aspiration pneumonia.  The patient was healthy and worked as an engineer without difficulty until about 4 months ago.  Since that time, he has developed severe confusion, mood changes, and memory impairment and had to take medical leave from work.  The patient is now completely dependent on his wife for toileting, feeding, and general self-care.  Physical examination shows disorientation and sporadic, jerky extremity movements.  During hospitalization, the patient lapses into a coma and dies.  Postmortem examination of his brain shows widespread atrophy of the cerebral cortex and cerebellum.  Histologic analysis of the patient’s brain tissue would most likely show accumulation of which of the following?

A 56-year-old male with history of polycystic kidney disease presented to the emergency room because of sudden onset severe headache.  He has never had this type of headache in the past.  Examination shows some nuchal rigidity.  Neurologic examination is within normal limits.  Which of the following is the most likely diagnosis?

A 35-year-old woman comes to the office due to trouble seeing out of her right eye.  The patient started having blurry vision and pain with eye movement 2 days ago.  She has no headache, vertigo, slurred speech, numbness, or weakness.  Two years ago, the patient had an episode of double vision that spontaneously resolved after a few weeks.  On physical examination, she has an afferent pupillary defect with markedly reduced visual acuity on the right.  Funduscopy reveals blurring of the optic disk margins in the right eye.  MRI of the brain reveals multiple, ovoid white matter lesions with perpendicular orientation to the lateral ventricles.  This patient’s condition is most likely caused by an inappropriate immune response directed against which of the following cells?

A 71-year-old woman is brought to the physician by her daughter.  She says that her mother went shopping yesterday and could not find her way back home.  Two years ago, her mother “started forgetting things like where she put her keys” and “began to have problems remembering the right words.”  Now she has trouble keeping up with her activities of daily living and refuses to pay her bills because “it’s a waste of money.”  The patient’s past medical history is unremarkable.  Brain magnetic resonance imaging (MRI) is most likely to show atrophy of which of the following structures?

A 54-year-old man is brought to the office by his daughter.  She says that her father has been acting strangely over the past 2 years.  He makes inappropriate sexual jokes, has little regard for social rules, is often irritable, and is borderline aggressive at times.  The patient denies that his personality is any different from normal.  When speaking with the patient, the physician notices that he has minimal verbal output and repeats “it is what it is” when asked questions about his strange behavior.  On physical examination, he appears unkempt but otherwise has no significant findings.  This patient most likely has a condition that predominantly involves which of the following structures?

A 10-year-old boy whose family recently immigrated to the United States is brought to the physician with ataxia, myoclonus, and visual problems.  His parents say that he began acting strangely and having difficulty with school work several months ago.  After the appropriate workup, a brain biopsy is obtained and an RNA virus containing hemagglutinin is cultured from the tissue sample.  Which of the following is the most likely diagnosis?

A 34-year-old man comes to the emergency department due to severe headache.  The patient describes unbearable, throbbing pain around his right eye that awakened him.  Over the past week, he has had several similar episodes, which spontaneously resolved after 20-30 minutes.  He has no other medical conditions and takes no medications.  The patient smokes a pack of cigarettes daily and drinks alcohol on social occasions.  On physical examination, he appears restless and paces in the room.  There is mild conjunctival injection and miosis of the right eye.  Neurologic examination shows no abnormalities.  Which of the following is the most likely cause of this patient’s current symptoms?

A 44-year-old man with a history of advanced HIV is brought to the office by his family due to progressive cognitive decline.  Over the last several years he has had worsening memory deficits and difficulty carrying out simple mental tasks.  The patient has had no headaches, slurred speech, muscle weakness, or changes in vision.  He was diagnosed with HIV 7 years ago, but his medical follow-up and treatment compliance have been poor.  The patient does not use tobacco, alcohol, or recreational drugs.  Vital signs are normal.  He has difficulty with delayed recall as well as several executive function tasks.  The remainder of his neurologic examination is unremarkable.  Two weeks later, he dies from severe pneumonia and respiratory failure.  Which of the following histopathologic findings would most likely be found on biopsy of this patient’s brain?

A 66-year-old man comes to the emergency department due to dizziness, dysarthria, and bilateral limb ataxia.  His symptoms have been steadily worsening over the last 2 weeks.  He has no other medical problems and takes no medications.  He has a 50-pack-year smoking history and does not use alcohol or illicit drugs.  Chest x-ray shows a mass in his right lung.  He is admitted to the hospital for evaluation, but his neurologic symptoms continue to progress.  He dies several months later despite receiving appropriate treatment.  Autopsy shows extensive cerebellar Purkinje cell degeneration.  Which of the following best describes the etiology of this patient’s neurologic condition?

An 82-year-old man is brought to the emergency department after multiple falls.  He has had severe back pain over the last month, for which he has been taking over-the-counter pain medication without significant relief.  Over the last week, the patient has noted weakness in his legs bilaterally, and his gait has become unstable.  Medical history is significant for hypertension, hyperlipidemia, coronary artery disease, and gout.  The patient has lost 6.8 kg (15 lb) in the last month due to poor appetite.  Rectal examination reveals an enlarged, firm, nodular prostate.  Which of the following is the most likely cause of this patient’s current symptoms?

A 75-year-old man is brought to the emergency department due to problems with vision and right-sided hemisensory loss that started an hour ago.  While in the emergency department, his symptoms gradually worsen and he develops a headache.  Head CT reveals multiple, small lobar hemorrhages of varying ages in the occipital and parietal areas with a medium-size acute bleed in the left parietooccipital lobe.  Two years ago, the patient developed sudden right arm weakness; neuroimaging at that time demonstrated a small left frontal lobe hemorrhage.  He has no head trauma and does not use anticoagulants.  This patient most likely suffers from which of the following?

A 56-year-old woman is brought to the emergency department after a generalized tonic-clonic seizure witnessed by her husband.  The patient has no history of seizures or other medical conditions but has been having recurrent headaches for the past several months.  Physical examination shows mild weakness with increased deep tendon reflexes in the left upper extremity.  MR imaging of the brain reveals a large mass in the right frontal lobe.  Stereotactic biopsy of the mass yields hypercellular white matter with extensive astrocytic aberration, microvascular proliferation, and areas of necrosis lined by tumor cells.  Molecular studies of the abnormal cells are most likely to demonstrate which of the following findings?

A researcher conducts a study to evaluate the morphological changes of various cerebral pathologies using live animal models.  In an experiment, histopathological examination of the brain after an inciting event shows neurons with intensely eosinophilic cytoplasm and condensed basophilic nuclei.  Serial biopsies are obtained to evaluate progressive changes.  Which of the following is most likely to be seen in the affected brain area in the subsequent weeks?

A 46-year-old woman comes to the emergency department due to sudden-onset, severe occipital headache and nausea.  The patient has a history of hypertension and cigarette smoking.  Physical examination shows mild disorientation but no focal weakness, sensory loss, or cranial nerve abnormalities.  Noncontrast CT scan of the head reveals diffuse hyperdensity in the subarachnoid space.  CT angiography reveals a ruptured anterior communicating artery aneurysm.  The patient undergoes endovascular coiling of the aneurysm.  Four days later, there is sudden deterioration in her level of consciousness and new, right-sided hemiparesis is observed.  Repeat CT scan shows no significant changes.  Which of the following is the most likely cause of this patient’s neurological deterioration?

A 36-year-old man comes to the office due to involuntary deviation of the head to the right, accompanied by muscle pain in his neck.  The head-turning occurs in spells that start spontaneously, last 30-40 minutes, and is sometimes suppressed by placing a hand on the chin.  Between episodes, there are no symptoms.  This patient’s condition is best characterized as which of the following?

A 55-year-old, right-handed woman is brought to the emergency department due to acute-onset headache and difficulty with vision.  En route to the hospital, she becomes unconscious.  Medical history is significant for hypertension.  Blood pressure is 150/90 mm Hg and pulse is 90/min and regular.  CT scan of the head without contrast demonstrates an acute hemorrhage in the left temporal lobe with compression of the anterior medial temporal lobe against the free margin of the tentorium cerebelli.  Which of the following cranial nerves is most likely to be compromised in this patient?

A previously healthy 16-year-old boy is evaluated for progressive headaches and blurred vision that started several months ago.  The headaches are more severe upon waking up in the morning and are often accompanied by nausea and vomiting.  He takes no medications and does not use tobacco, alcohol, or illicit drugs.  Physical examination is notable for bilateral papilledema.  MRI of the brain is shown in the exhibit.  This patient’s brain lesion most likely originated from which of the following cells?

A 58-year-old homeless man is brought to the emergency department after being found unresponsive on a sidewalk.  The patient has been hospitalized on several occasions for alcohol and illicit drug intoxication.  He also has a history of hypertension but is not adherent with medical therapy.  On arrival, the patient is obtunded, febrile, and hypotensive.  Physical examination reveals lung crackles and a new blowing diastolic murmur consistent with aortic regurgitation.  Appropriate treatment is started, but the patient dies several days later.  Autopsy examination shows symmetric, bilateral wedge-shaped strips of necrosis over the cerebral convexity, parallel and a few centimeters lateral to the interhemispheric cerebral fissure.  Which of the following is the most likely cause of this patient’s cerebral findings?

Magnetic resonance imaging of the head of a young patient shows an angiomatous lesion involving the cerebellum.  There is also a cystic mass in the right kidney on abdominal ultrasound.  The differential diagnosis must include which of the following?