Meninges
Cerebrospinal fluid circulates within this meningeal space.
What is the subarachnoid space?
Why does aqueductal stenosis enlarge the lateral and third ventricles but spare the fourth ventricle?
The obstruction is proximal to the fourth ventricle.
A patient with a blown right pupil and left hemiparesis has compression of which nerve and which motor pathway/area?
Right CN III and right cerebral peduncle.
What is the earliest symptom of normal pressure hydrocephalus?
Magnetic gait
A patient develops fever, severe back pain, urinary retention, and leg weakness. What diagnosis must be excluded first?
Spinal epidural abscess
A patient develops a rapidly expanding biconvex hemorrhage after temporal bone trauma. Which artery is injured, and between which two layers does blood accumulate?
What is Middle meningeal artery; periosteal dura and skull (epidural space)
This dural fold separates the cerebral hemispheres.
What is the falx cerebri?
This herniation syndrome causes respiratory arrest by compressing the medulla.
What is tonsillar herniation?
Which patients require CT imaging before lumbar puncture when meningitis is suspected?
Immunocompromised, focal deficits, papilledema, recent seizure, markedly altered consciousness, known CNS lesion.
A patient with chronic sinusitis develops headache, fever, seizures, and a crescentic extra-axial collection on MRI. Diagnosis?
Subdural empyema.
A crescentic extra-axial hemorrhage crosses sutures but not the falx. Which vessels were likely torn, and why can symptoms evolve slowly?
What is Bridging veins; low-pressure venous bleeding?
A patient develops communicating hydrocephalus after aneurysmal SAH. What is the underlying pathophysiology?
Fibrosis/dysfunction of arachnoid granulations causing impaired CSF absorption.
Why can a right uncal herniation occasionally produce right-sided weakness?
Kernohan notch phenomenon—compression of the contralateral cerebral peduncle.
This is the most common organism causing spinal epidural abscess.
Staph aureus
A patient with worsening headache has MRI demonstrating enlargement of the lateral ventricles only. The third and fourth ventricles are normal.
Where is the obstruction?
Foramen of Monro
This dural fold separates the cerebral hemispheres.
What is the falx cerebri?
Which circumventricular organ detects circulating toxins and why is it able to do so?
Area postrema; lacks an intact BBB.
A patient presents with isolated left leg weakness after rapid expansion of a frontal mass. Which herniation syndrome has likely occurred?
Subfalcine herniation with ACA compression.
A patient with aneurysmal subarachnoid hemorrhage becomes progressively confused on hospital day 2. CT demonstrates enlarging ventricles without new hemorrhage. What is the diagnosis, and what is the next step in management?
Acute communicating hydrocephalus due to impaired CSF absorption from subarachnoid blood. Management is urgent CSF diversion with an external ventricular drain (EVD).
A posterior fossa mass patient becomes acutely obtunded after placement of a lumbar drain.
What catastrophic complication occurred?
Downward (tonsillar) herniation precipitated by CSF removal.
A lumbar puncture enters which anatomic space, and through which two meningeal layers must the needle pass immediately before entering CSF?
What is the subarachnoid space; the arachnoid mater and pia mater?
Name the two openings through which CSF exits the fourth ventricle.
What are the foramen of Magendie and the foramina of Luschka?
Name and deficits caused by syndrome that results from compression of the dorsal midbrain by an enlarged third ventricle.
Parinaud, an inability to look upward, large pupils that do not react to light but constrict during focusing (light-near dissociation), and abnormal eye jerking when attempting upward gaze (convergence-retraction nystagmus)
A patient has ventriculomegaly but diffuse severe cortical atrophy. What imaging finding would argue against NPH?
Ventricular enlargement proportional to cortical atrophy (hydrocephalus ex vacuo).
A 26-year-old with a history of recurrent headaches presents with acute coma. CT demonstrates a hyperdense round lesion at the anterior third ventricle with marked enlargement of both lateral ventricles.
What is the diagnosis, and why can symptoms be intermittent before presentation?
Colloid cyst of the foramen of Monro; intermittent obstruction of CSF flow ("ball-valve" effect) causes episodic headaches before acute obstructive hydrocephalus.