A 22-year-old man comes to the office due to occasional dull headaches that awaken him from sleep.  The patient has no associated neurologic deficits.  There is no history of migraines in the family.  His temperature is 37.2 C (99 F), blood pressure is 140/80 mm Hg, pulse is 60/min, and respirations are 12/min.  On physical examination, there are several 3- to 5-cm flat, pigmented spots on his trunk.  There are also multiple, subcentimeter, soft, fleshy, cutaneous tumors located on his trunk and neck.  The predominant cells forming these tumors most likely originated from which of the following structures?

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?

A 23-year-old woman is brought to the emergency department unconscious after a motor vehicle accident.  The patient was texting on her cell phone and was not wearing a seatbelt during the incident.  She has no known medical problems and takes no medications.  Her temperature is 36.7 C (98 F), blood pressure is 155/90 mm Hg, pulse is 62/min, and respirations are 10/min.  A linear skull fracture at the junction of the frontal, parietal, temporal, and sphenoid bones is seen on head CT scan.  A branch of which of the following arteries is most likely severed in this patient?

A 64-year-old man with type 2 diabetes mellitus is evaluated in the clinic due to occasional dizziness.  His symptoms usually occur while playing table tennis.  The patient has not had any falls or loss of consciousness.  He has no known history of coronary artery disease or stroke.  The patient has smoked a pack of cigarettes daily for the past 40 years and occasionally drinks alcohol.  Orthostatic vital signs are normal.  ECG shows normal sinus rhythm.  Doppler ultrasound evaluation of the left vertebral artery reveals retrograde (caudal) flow instead of normal antegrade flow.  Which of the following arteries is most likely to be occluded based on these ultrasound findings?

A 71-year-old man comes to the emergency department due to sudden-onset vision loss in his left eye for one hour.  He has a history of coronary artery disease, hypertension, and type 2 diabetes mellitus.  Blood pressure is 145/80 mm Hg and pulse is 72/min.  On examination, the patient can see only hand motions through the left eye.  Funduscopic evaluation of the eye shows a cherry-red spot in the macula with surrounding retinal whitening.  Cranial nerve examination is otherwise unremarkable.  There is a left-sided neck bruit on cardiovascular examination.  Which of the following is the most likely path of the embolus causing this patient’s symptoms?

A 32-year-old woman is evaluated for pain and a palpable mass in the right flank.  Imaging studies reveal a large mass arising from the right kidney and similar smaller masses in the left kidney.  Surgery to remove the right-sided tumor along with the right kidney is performed; a cross section of the specimen is shown in the image below.

Histopathologic evaluation shows that the mass is composed of fat, smooth muscle, and blood vessels.  This patient is most likely to have which of the following additional findings?

A 3-year-old girl is brought to the emergency department due to worsening fever and lethargy.  Her parents report that she has had recurrent upper respiratory illness and recently had been irritable and pulling at her ears.  She has also been eating poorly and vomiting, and has progressively become more lethargic.  The patient has no chronic medical conditions and has received all recommended vaccinations.  While being evaluated in the emergency department, she has a generalized tonic-clonic seizure.  CT scan of the head shows a solitary 2-cm, ring-enhancing lesion in the left lateral temporal lobe.  The pathogen responsible for this patient’s current condition most likely gained access to the brain from which of the following structures?

A 65-year-old man comes to the emergency department due to sudden-onset headache.  The patient has had no recent falls or head trauma.  Medical history includes hypertension and lung adenocarcinoma with abdominal metastasis.  Initial noncontrast CT scan of the head reveals a small temporal lobe hemorrhage.  Over the next 24 hours, the patient becomes progressively obtunded and develops generalized tonic-clonic seizures.  Blood pressure is 190/96 mm Hg, pulse is 38/min, and respirations are 10/min with brief episodes of apnea.  A repeat noncontrast CT scan of the head reveals acute hemorrhage expansion with brain herniation.  Which of the following findings is most likely to be observed on this patient’s repeat neurologic examination?

A 4-day-old premature infant in the neonatal intensive care unit becomes hypotonic and less responsive.  She was delivered vaginally at 30 weeks gestation, and her birth weight was 1,200 g (2 lb 10 oz).  Physical examination shows a lethargic infant with weak and high-pitched crying, prominent scalp veins, and tense fontanelles.  Cranial ultrasound reveals blood in the lateral ventricles.  Which of the following structures is the most likely source of the bleeding?

A 65-year-old man is brought to the emergency department due to acute-onset, right-sided weakness and slurred speech.  He also has a severe headache and nausea.  Medical history is significant for poorly controlled hypertension and chronic tobacco use.  Blood pressure is 240/120 mm Hg and pulse is 104/min.  On physical examination, the patient is lethargic with right hemiparesis and lower facial weakness, right hemisensory loss, and dysarthria.  Noncontrast CT scan of the head is shown in the image below.

Which of the following cerebral blood vessels is most likely affected in this patient?

A 31-year-old female with new-onset generalized tonic-clonic seizures has an intracranial mass detected on head CT scan.  Biopsy of the mass reveals neoplastic cells that stain positive for synaptophysin and negative for glial fibrillary acidic protein.  These neoplastic cells most likely originate from the same precursor tissue as which of the following?

A 34-year-old man is evaluated in the clinic due to persistent buzzing in his right ear for the past 6 months.  The patient also has decreased hearing on the right side.  He has had no fever, ear pain, runny nose, sore throat, or cough.  The patient does not use cotton swabs and has not been exposed to loud noise.  He tried using over-the-counter oral pseudoephedrine with no improvement in his symptoms.  On physical examination, there is no sinus tenderness, and mucous membranes are moist without erythema or exudate.  Otoscopic examination reveals normal-appearing external auditory canals bilaterally with pinkish-grey tympanic membranes.  MRI of the brain reveals an intracranial tumor.  This patient’s lesion has most likely arisen from which of the following structures?

A 43-year-old male with advanced HIV is hospitalized for evaluation of recent-onset headaches and personality changes.  Imaging of the brain shows a solitary mass within the temporal lobe.  Biopsy of the mass reveals uniform cells containing the Epstein-Barr virus genome.  This patient most likely suffers from which of the following?

A 32-year-old man is brought to the emergency department due to weakness and tingling that started in his feet and is now at his knees.  A week ago, the patient noticed that his legs felt weak while climbing stairs.  Since then, the weakness has progressively worsened every day.  Today, he fell twice when attempting to walk.  Medical history is insignificant, except for a mild respiratory infection 2 weeks ago that resolved spontaneously.  The patient does not use tobacco, alcohol, or illicit drugs.  He takes no medications.  Vital signs are within normal limits.  Physical examination shows marked weakness in the distal muscles and moderate weakness in the proximal muscles in both legs.  Deep tendon reflexes are absent at the knees.  This patient’s condition is most likely associated with which of the following?

A 12-year-old boy is evaluated for chronic headaches and visual changes.  The headaches have progressively worsened over the past year and are associated with nausea.  The patient’s parents are especially concerned as his symptoms have been interfering with his coursework in middle school.  An intracranial calcified mass is detected on brain imaging.  The mass is surgically removed and on gross inspection shows cystic spaces filled with thick, brownish-yellow fluid that is rich in cholesterol.  This mass is most likely derived from cells responsible for forming which of the following structures?

A 75-year-old man is brought to the emergency department due to 2 hours of left-sided chest pain and dyspnea.  The patient has lived in a skilled nursing facility since developing right-sided hemiplegia, hemi-sensory loss, and aphasia 4 months ago.  He has a history of diabetes mellitus, hypertension, and hypercholesterolemia.  As an ECG is being obtained, the patient develops ventricular fibrillation and dies despite resuscitative efforts.  An autopsy is performed; a coronal section of the brain is shown in the image below.

The walls of the brain lesion are most likely composed of which of the following?

A 68-year-old woman comes to the office due to tingling and numbness affecting her hands and legs.  The patient’s symptoms began 2 years ago with a “pins-and-needles” sensation in the soles of her feet, which has since progressed slowly upward to the mid-calf level.  Lately, she has also had similar symptoms in her fingers.  The patient has a 15-year history of type 2 diabetes mellitus complicated by diabetic retinopathy.  Other medical conditions include hypertension and osteoarthritis.  On physical examination, ankle reflexes are absent and sensation of joint position is decreased in the toes.  Romberg sign is present.  A lesion involving which of the following best explains this patient’s findings?

A 32-year-old woman comes to the office due to left eye pain that is accentuated by ocular movements.  She also has periodic dimming of vision in the same eye.  The patient has had several such episodes over the last month, most often after a hot shower or intense workout.  A year ago, she had an episode of numbness and tingling in her left arm that resolved spontaneously.  The patient has no other medical issues and takes no medication.  She smokes half a pack of cigarettes a day and does not use alcohol or illicit drugs.  Vital signs are normal.  BMI is 26 kg/m².  Ophthalmologic examination shows swelling of the optic disc on the left.  Neurologic examination shows a mild intention tremor and broad-based gait.  Which of the following is the most likely cause of the patient’s current condition?

A 60-year-old professor is brought to the emergency department after developing right-sided weakness and numbness during a lecture an hour ago.  He also has nausea and confusion.  The patient smoked a pack of cigarettes daily for 20 years but quit 10 years ago.  He does not drink alcohol.  His father died of myocardial infarction at age 70.  Blood pressure is 190/100 mm Hg, and pulse is 60 /min.  On physical examination, there are no signs of head trauma.  There is diminished right-sided strength (1/5) and an upgoing plantar reflex.  Brain CT without contrast is obtained immediately.  The image is shown below.

Which of the following is the most likely cause of this patient’s condition?

A 22-year-old woman comes to the emergency department due to acute vision disturbances and headache.  About an hour ago the patient experienced a small area of visual loss, which she describes as a hole in the visual field.  The vision disturbance gradually expanded to a C-shape in her peripheral vision and spontaneously resolved after 15-20 minutes.  A progressively worsening, severe, right-sided headache of pulsating quality quickly followed.  The patient has had similar headaches in the past but not of such severity.  She has no other medical conditions and takes no medications.  Blood pressure is 150/86 mm Hg and pulse is 92/min.  On physical examination, the patient is lying still in bed with eyes closed.  The pupils are equal and reactive to light.  Funduscopic examination reveals no abnormalities.  Bilateral upper and lower extremity muscle strength, deep tendon reflexes, and sensation are normal.  Which of the following is the most likely diagnosis?

A study was conducted to determine the utility of adjunctive therapy in bacterial meningitis.  Patients with acute bacterial meningitis whose cerebrospinal fluid (CSF) analysis showed gram-positive diplococci were divided into 2 groups.  The first (control) group was given systemic antibiotics only, and the second (experimental) group was given dexamethasone followed by systemic antibiotics.  Compared to the control group, patients in the experimental group developed fewer neurologic sequelae and had a lower risk of death.  The experimental patients most likely benefited from the use of this drug due to which of the following?

An 82-year-old man is found unresponsive by his neighbor.  The patient lives alone in his suburban home.  When the neighbor went to check on him, the patient was on the floor and not answering any questions.  His medical history is unknown.  On arrival of emergency medical services, the patient is obtunded and responds only to painful stimuli.  Supportive measures are begun, including endotracheal intubation, but the patient dies en route to the hospital.  Autopsy reveals extensive atherosclerotic disease involving the coronary and internal carotid arteries.  Histopathologic examination of the brain in the right middle cerebral artery territory shows neurons with intensely eosinophilic cytoplasm and nuclear fragmentation.  Based on these findings, this patient’s cerebral injury most likely occurred approximately how long ago?

A 54-year-old hospitalized man develops new-onset slurring of speech and extremity weakness.  Medical history is significant for alcohol abuse.  Physical examination reveals confusion, dysarthria, dysphagia, and quadriparesis.  MRI of the brain shows symmetric areas of demyelination in the pons.  Which of the following most likely predisposed this patient to his current condition?

An intracranial mass is removed from a 33-year-old patient.  The mass is composed of cells that have elongated, wavy nuclei.  A biphasic pattern of growth is identified, consisting of areas of dense cellularity interspersed with less dense myxoid regions.  The cells show diffuse S-100 immunoreactivity.  Which of the following is the most likely diagnosis?

A 64-year-old man comes to the emergency department due to left lower extremity weakness.  The patient was asymptomatic when he went to bed the night before, but he has had difficulty standing after waking up today.  He has had no headache, double vision, or back pain.  Medical history is significant for hypertension, diabetes mellitus, and myocardial infarction.  Temperature is 37 C (98.6 F), blood pressure is 140/90 mm Hg, and pulse is 110/min and irregularly irregular.  Left lower extremity examination shows motor power is 0/5, deep tendon reflexes are 3+, and Babinski sign is present.  Right lower extremity examination is normal.  An abnormality in which of the following structures is the most likely cause of this patient’s symptoms?

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?

A 4-year-old boy is brought to the office due to headaches that have worsened progressively over the past month and are most severe when lying down.  He also has had nonbloody, nonbilious emesis for 2 weeks that typically occurs early in the morning.  In addition, the child has intermittent blurry vision, particularly when looking up at the mirror while brushing his teeth.  Physical examination shows bilateral papilledema, inability to gaze upwards, and bilateral eyelid retraction.  Laboratory testing of sodium, growth hormone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) is normal.  Given the early morning emesis and papilledema, a brain mass is suspected and a brain MRI is ordered.  Which of the following is the most likely location of the brain lesion in this patient?