An 18-year-old previously healthy woman is brought to the emergency department with 2 days of fever, headache, and lethargy.  She has also had nausea and several episodes of vomiting.  Her temperature is 38.9 C (102 F), blood pressure is 110/60 mm Hg, and pulse is 108/min.  On physical examination, the patient is diaphoretic, delirious, and has a petechial rash on the trunk and extremities.  Signs of meningeal irritation are present.  CT scan of the head reveals no mass lesions.  She is scheduled for a lumbar puncture for cerebrospinal fluid analysis.  During this procedure, which of the following anatomical landmarks helps locate the optimal site for needle insertion?

A 70-year-old, right-handed woman comes to the emergency department with a daylong history of vision disturbance and bumping into objects on the left side.  She also has had a mild headache over the past several hours.  Medical history includes hypertension, hyperlipidemia, and type 2 diabetes mellitus.  Physical examination shows left homonymous hemianopia with macular sparing.  Noncontrast CT of the head demonstrates an area of focal parenchymal hypoattenuation consistent with ischemic infarction, as shown in the image below:

Which of the following additional examination findings is most likely to be present in this patient?

A 55-year-old man with poorly controlled hypertension and type 2 diabetes mellitus comes to the emergency department due to difficulty seeing.  He has had blurry vision for the last 2 weeks, and 1 day ago he suddenly noticed a shadow develop across the visual field of his left eye.  The patient has no recent headache, double vision, vertigo, light sensitivity, or nausea.  On examination, pupils are equal and reactive to light.  There is an area of reduced vision in the left eye.  Funduscopic examination reveals a flame-shaped hemorrhage in the left temporal hemiretina.  Transmission of visual information to which of the following structures is most likely impaired in this patient?

A 54-year-old man is brought to the emergency department by his wife after he develops difficulty speaking.  When asked about the onset of his symptoms, the patient slowly responds with “I… weak… morning…” and becomes very frustrated.  His wife says that he was able to grasp a pen without any problem while completing medical release forms, but had trouble signing his name.  On examination, he is able to state his first name but with difficulty, and correctly points to different body parts on command.  He also has mild weakness involving his right arm and face.  This patient’s speech difficulties are most likely caused by a lesion affecting which of the following brain areas?

A 16-year-old boy is brought to the emergency department after an eye injury during a baseball game.  He was batting for his high school team when the opposing pitcher made a wild throw and the baseball hit him in the right eye.  The patient has since been having diplopia that worsens when he looks up.  On physical examination, he has mild periorbital ecchymosis, enophthalmos, and limited vertical movement of the right eye.  Visual acuity and left eye examination are normal.  CT scan of the head reveals an orbital floor fracture.  Which of the following additional findings is most likely to be seen in this patient?

A 34-year-old man is evaluated in the clinic due to difficulty walking over the past 2 weeks.  His symptoms have resulted in several recent falls, but he has had no head trauma or loss of consciousness.  He has never had these symptoms before.  The patient is frustrated as he cannot carry out his duties as a mailman.  He has a history of crack cocaine use in the distant past but no current illicit drug use.  The patient is in a monogamous relationship but previously had numerous sexual partners.  The physician asks him to stand with his feet close together, arms to the sides, and eyes closed.  This maneuver most likely tests for abnormalities in which of the following?

An 18-year-old woman is brought to the emergency department by her parents for altered mental status that began today.  Two months ago, the patient began restricting her dietary intake due to fear of being overweight.  Since then, she has experienced notable weight loss and has felt weaker overall.  The patient’s parents have been encouraging her to eat, and today, she agreed to eat watermelon and pineapple for breakfast.  Afterward, she fell while walking and appeared very somnolent.  The patient is otherwise healthy with no chronic medical conditions and takes no medications.  BMI is 16 kg/m², decreased from 18.5 kg/m² a few months ago.  The patient is oriented to name only and has a poor attention span.  Pupils are equal and reactive, but she has nystagmus and lateral gaze palsy.  Strength and sensations are equal in the bilateral extremities.  The patient walks in short steps and has difficulty maintaining her balance.  Abdominal and skin examinations are unremarkable.  Head imaging reveals no hemorrhage.  This patient’s clinical findings are most likely due to which of the following?

A highly agitated 54-year-old man is brought to the emergency department by his family because he is unable to effectively communicate.  He speaks clearly and with conviction but his sentences are incomprehensible.  He does not appear to understand the doctor’s questions, does not follow oral or written instructions, and cannot repeat simple phrases.  Branch occlusion of which of the following arteries is most likely responsible for this patient’s condition?

A 42-year-old woman comes to the office due to dizziness.  She has a 6-month history of episodic bouts where she experiences a spinning sensation associated with nausea and ringing in her left ear.  The patient also has difficulty hearing while holding her phone to the left ear, although hearing in the right ear is normal.  The dizziness improves spontaneously and she feels fine between episodes.  Past medical history is notable for hypothyroidism, for which she is on thyroid replacement therapy, and endometriosis, which led to a hysterectomy at age 38.  The patient works as a supermarket manager.  She does not use tobacco or drink alcohol.  This patient’s condition is most likely the result of which of the following pathologic processes?

A 48-year-old woman comes to the office due to an intermittent ear discharge over the last 2 years.  She has also noticed decreased hearing in the right ear recently.  Past medical history is significant for obesity, hyperlipidemia, seasonal allergies, and diet-controlled diabetes mellitus.  Otoscopy shows a small perforation in the right tympanic membrane and a pearly mass behind the membrane.  Conduction hearing loss is noted in the right ear.  The remainder of the ear, nose, and throat examination is normal.  Which of the following is the most likely cause of this patient’s aural mass?

A 37-year-old previously healthy man comes to the office for evaluation of enlarged lymph nodes.  He has an 8-week history of progressively enlarging cervical lymph nodes associated with subjective fevers, fatigue, and drenching night sweats.  After initial assessment, the patient undergoes excisional biopsy of enlarged lymph nodes in the left posterior triangle of the neck.  Two weeks later, during a follow-up visit, he describes difficulty with overhead activities such as combing his hair or placing dishes on overhead shelves.  Examination shows a left shoulder droop with weakness of left arm abduction above 100 degrees.  Other shoulder movements are normal, and there is no sensory loss.  Which of the following muscles is most likely paralyzed in this patient?

A 56-year-old previously healthy man comes to the office due to decreased hearing in both ears.  He reports difficulty understanding conversations in crowded rooms.  His wife adds that they often argue about the volume of the television set.  The patient cannot remember precisely when he first noticed hearing loss but says it has been present at least 6 months and is getting worse.  For the past 12 years, he has worked in a factory where he has to shout to communicate with coworkers and has seldom worn hearing protection.  An audiogram is obtained as shown in the image below.

Which of the following is most likely abnormal in this patient?

A 23-year-old man comes to the emergency department due to a sensation of food being stuck in his throat.  His symptoms started 2 hours ago after eating fish at a local seafood restaurant.  He has tried swallowing multiple times to clear the food with no relief.  The patient has no difficulty with breathing.  He does not appear to be in significant distress on physical examination.  Laryngoscopy reveals a fish bone lodged in the left piriform recess.  During retrieval of the fish bone, a nerve is injured deep to the mucosa overlying the recess.  Which of the following is most likely to be impaired in this patient?

A 37-year-old man comes to the office due to difficulty sleeping.  He says that his new job as a business executive is very stressful and requires considerable travel.  During the past 3 months, the patient has made numerous trips between the United States and France.  He frequently experiences insomnia and daytime sleepiness for several days after he travels, but his sleep improves significantly thereafter.  Which of the following hypothalamic nuclei is most likely responsible for this patient’s symptoms?

A 15-year-old boy comes to the office due to right ear itching and discomfort for the past several days.  He has no fever or hearing loss but has noted scant drainage of thin, whitish fluid.  The patient has been taking swimming lessons at a local gym.  On examination, there is no redness around the ear, but gentle traction of the pinna elicits pain.  During inspection of the external auditory canal, a speculum is inserted into the meatus in close contact with its posterior wall, causing the patient to suddenly become lightheaded and faint.  He recovers spontaneously within a few minutes with no residual confusion.  Which of the following nerves was most likely irritated during the procedure?

A 35-year-old woman with a history of migraines is evaluated due to a recent increase in headache frequency and severity.  She has had no focal weakness, sensory loss, vision changes, or seizures.  The patient has no other medical conditions and takes sumatriptan as needed.  She does not use tobacco, alcohol, or illicit drugs.  Physical examination shows no focal neurological deficits.  Neuroimaging reveals a small aneurysm arising from the segment of right internal carotid artery within the cavernous sinus.  If this patient’s aneurysm continues to expand, which of the following findings is most likely to be observed?

A 15-year-old girl comes to the office with gait instability.  Since age 12, the patient has had mild weakness and “clumsiness” in her lower limbs that have progressed.  She has to hold on to the railing when walking down stairs due to several recent falls.  Physical examination reveals kyphoscoliosis, pes cavus, and bilateral lower extremity ataxia.  Joint position and vibration sense are also impaired.  Further evaluation reveals that she is suffering from an inherited disease.  This patient is at greatest risk of dying from which of the following conditions?

A 65-year-old man is brought to the emergency department due to acute onset of a severe headache and dizziness.  He describes it as a throbbing that localizes to the back of his head, with associated vertigo and mild nausea.  The patient has a past medical history of type 2 diabetes mellitus, hypertension, chronic obstructive pulmonary disease, and a recent diagnosis of lung adenocarcinoma.  He has smoked 1-2 packs of cigarettes daily for the past 30 years.  His temperature is 36.7 C (98 F), blood pressure is 170/96 mm Hg, pulse is 80/min, and respirations are 14/min.  Noncontrast head CT reveals an acute hemorrhage in the cerebellar vermis without mass effect or midline shift.  Which of the following neurologic findings is most likely to be present during this patient’s physical examination?

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?

A 52-year-old man is brought to the office due to social withdrawal and inability to care for himself.  The patient is divorced and lives alone, and he was found to be living in disarray by his daughter, who is visiting from out of state.  His neighbors and friends say the patient rarely comes out of the house or contacts them.  During previous visits, his daughter noticed fidgety movements of his hands, but now he has marked jerky movements of his extremities with frequent facial grimaces.  He has a history of depression with frequent angry outbursts that led to his divorce several years ago.  The patient has no other medical conditions and does not use tobacco, alcohol, or illicit drugs.  He was adopted and his family history is unknown.  On physical examination, the patient is forgetful and has slowed mental processing.  Involuntary, spasmodic movements of the hands and facial muscles are present.  Deep tendon reflexes and sensation are normal.  The loss of neurons supplying which of the following neurotransmitters is most specific for this patient’s disease process?

A 58-year-old man comes to the emergency department due to sudden right-sided weakness.  He has no sensory loss, problems speaking/swallowing, or difficulty with balance.  The patient was previously told that he has elevated blood pressure, but he does not routinely follow up with his physician.  He takes no medications.  Examination shows intact cranial nerves and sensory function.  The patient has 3/5 muscle strength on the right side.  Initial CT scan without contrast reveals no abnormalities.  Four weeks later, repeat brain imaging shows a 9-mm, fluid-filled cavitary lesion in the left internal capsule.  This patient’s condition is most likely caused by which of the following?

A gross brain section of a 54-year-old male who suffered from severe tuberculous meningitis is shown below.

This patient’s condition is most likely related to impaired function of which of the following?

A 16-year-old boy is evaluated for progressive gait instability, dysmetria, and dysarthria for the past several years.  The patient enjoys basketball but can no longer play due to his worsening symptoms.  He is worried because his brother developed similar symptoms and died at age 21.  Physical examination of the lower extremities reveals bilateral motor weakness and loss of deep tendon reflexes, joint position, and vibration sense.  MRI of the brain and spine shows degeneration of the posterior columns and spinocerebellar tracts.  Which of the following conditions has neurologic manifestations that most closely resemble this patient’s disease?

A 64-year-old woman is evaluated for progressive gait disturbance over the last 2 years.  The patient feels her feet are “stuck on the floor” and that she is unsteady while walking.  She also recently began experiencing urinary urgency and has wet herself several times due to difficulty getting to the bathroom on time.  The patient stopped working 6 months ago because of difficulty concentrating, and she has also lost interest in her hobbies and social activities.  She has had no tremor, visual changes, headaches, nausea, or vomiting.  The patient has a remote history of closed traumatic brain injury.  Vital signs are within normal limits.  On physical examination, lower extremity tone and deep tendon reflexes are increased.  Sensation to light touch, pain, and vibration are normal.  The patient’s gait is slow with small steps and a wide base.  CT scan of the head is shown below.

Which of the following is the most likely diagnosis?

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?

A 54-year-old woman is brought to the emergency department due to acute-onset mental status changes and double vision.  Examination shows that the patient is awake but disorientated to time and place and has a decreased attention span.  Further questioning reveals memory impairment that appears to have been most severe during the last few months.  Examination of the eyes shows horizontal nystagmus evoked on lateral gaze with bilateral weakness of the lateral rectus muscles.  Strength is equal bilaterally, but the patient is unable to walk without support.  She receives appropriate treatment based on the most likely diagnosis, and most of the clinical findings resolve.  However, she continues to have residual memory deficits.  This patient was most likely treated for which of the following conditions?

A 32-year-old woman describes five episodes of intractable vomiting over the last year.  The episodes last several hours and are associated with a sensation that the room is spinning or tilting.  At these times, it is difficult for her to walk because she loses her balance.  She cannot relate the timing of the episodes to any particular inciting event.  Physical examination reveals stability in the Romberg position and during tandem walk.  Proprioception is intact.  Dysfunction of which of the following structures best explains this patient’s symptoms?

A 63-year-old man collapses at home after experiencing severe retrosternal chest pain.  The emergency medical team finds him with no pulse, and cardiac monitoring shows ventricular fibrillation.  Cardiopulmonary resuscitation is performed, and the patient regains spontaneous circulation after several minutes.  On arrival at the hospital, he has stable vital signs but does not follow commands or respond to strong stimuli.  Which of the following areas is most likely to be affected first by ischemic damage in this patient?

A 65-year-old man comes to the office due to bothersome tremors.  The patient was diagnosed with idiopathic Parkinson disease 10 years ago and has since been successfully treated with levodopa-carbidopa.  However, over the last several months, he has developed frequent freezing episodes characterized by a sudden loss of mobility.  More recently, the patient’s tremors worsened after he reduced his levodopa dose following the development of involuntary body movements.  On examination, he has a bilateral resting tremor that is worse on the right, bradykinesia, and cogwheel rigidity.  His symptoms have significantly degraded his quality of life, and he is now interested in discussing surgical options.  This patient would benefit most from a treatment targeted at suppressing neuronal activity in which of the following brain structures?

A 43-year-old man comes to the office due to progressive memory loss and cognitive decline over the past several years.  Medical history includes HIV infection diagnosed 11 years ago.  Highly active antiretroviral therapy was prescribed, but he is nonadherent.  The patient describes concerns with attention, concentration, and speech.  In the past few months, he has become more apathetic and increasingly lethargic.  More recently, he has had difficulty with balance and has fallen on multiple occasions.  The patient has had no headache, tremor, vision change, fever, nausea, vomiting, or urinary incontinence.  His brother has a history of severe intellectual disability and epilepsy.  The patient scores 18/30 on the Mini-Mental State Examination and appears emotionally blunted.  He also has postural instability and difficulty performing fine motor tasks.  Noncontrast CT scan of the head is shown in the exhibits (2 images).  This patient’s condition can best be characterized as which of the following?

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?

A 42-year-old woman comes to the office with her husband for evaluation of abnormal movements.  The patient has been having involuntary facial grimaces and extremity fidgeting.  She has no prior medical or psychiatric conditions, but her husband says she has had frequent anger outbursts over the past year.  The patient takes no medications.  She smoked cigarettes and used illicit drugs for several years during college but not since then.  Her father died of a neurological disorder at age 55.  Physical examination shows intermittent, fidgety, jerky movements of the hands.  MRI of the brain is ordered.  Which of the following neuroimaging findings is most likely to be seen in this patient?

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?

A 15-year-old boy is brought to the office by his mother due to difficulty with movement.  The patient enjoys playing high school basketball but had to leave the team this year due to his progressively worsening symptoms.  On examination, he is found to have significant kyphoscoliosis and a high plantar arch.  His older brother suffered from a neurologic disorder and died of heart failure at age 25.  This patient most likely has which of the following neuropathologic findings?

A 62-year-old man comes to the office with his wife due to behavioral changes.  The patient has become increasingly impulsive and irritable over the past 1-2 years.  He recently lost his job after making inappropriate comments and touching female coworkers.  The patient has also lost interest in his hobbies and appears withdrawn during social gatherings.  His other medical problems are hypertension and hyperlipidemia.  A thorough neuropsychological assessment is conducted.  Inability to perform which of the following tasks would be most indicative of frontal lobe dysfunction?

A 65-year-old man is evaluated for right lower extremity weakness and difficulty walking.  The patient has a history of hypertension, type 2 diabetes mellitus, and osteoarthritis.  He has smoked a pack of cigarettes daily for 30 years.  During physical examination, the lateral border of his right sole is stroked using the blunt tip of a reflex hammer.  The maneuver, starting near the heel and proceeding to the base of the fifth toe, elicits extension of the great toe and fanning out of the other toes.  Which of the following additional findings is most likely to be observed in this patient’s right lower extremity?

A 6-month-old girl is brought to the clinic for a routine care appointment.  The patient has had no illnesses, although the mother says that she has trouble latching when breastfeeding.  She can roll over when prone but cannot roll from the supine position or sit unsupported.  The patient was born vaginally after an uncomplicated pregnancy.  Vital signs are within normal limits.  On physical examination, she has a head circumference above the 97th percentile for age and a full anterior fontanelle.  At birth, the patient’s head circumference was at the 50th percentile.  The remainder of the physical examination is unremarkable.  CT scan of the head reveals significant dilation of the lateral ventricles.  If this patient’s condition is left uncorrected, which of the following complications is most likely to develop?

A 67-year-old woman comes to the clinic due to decreased vision in her right eye that she noticed a week ago.  The patient says that her sight in the right eye is “narrower” than in the left.  Medical history is significant for hypertension, type 2 diabetes mellitus, and hyperlipidemia.  The patient also has intermittent lower limb claudication and has had 2 prior episodes of transient vision loss in her right eye.  Visual field testing reveals right nasal hemianopia.  MRI and MR angiography of the head and neck reveal a right internal carotid artery aneurysm.  Which of the following portions of the visual pathway is most likely disrupted in this patient?