Multiple Choice Questions on CSF Anatomy, Physiology, and Hydrocephalus for Neurosurgery
Question 1: Normal Pressure Hydrocephalus - Classic Presentation
A 72-year-old patient presents with progressive symptoms over 18 months. Which symptom typically appears FIRST in the classic NPH triad?
A) Urinary incontinence
B) Dementia with memory impairment
C) Gait disturbance
D) Headache
E) Visual changes
Correct Answer: C
Explanation: Gait disturbance is the cardinal and earliest sign of NPH, occurring in approximately 70% of patients and typically manifesting before cognitive impairment 1, 2. The gait abnormality is characterized by a hypokinetic pattern where feet appear "glued to the floor" or "magnetic" 3. Cognitive impairment develops later in the disease course, characterized by frontal lobe symptoms including psychomotor slowing and deficits in attention, working memory, and executive function 1. Urinary urgency occurs in approximately 48% of patients but is not the initial presenting symptom 2. The classic teaching that all three symptoms of the triad present simultaneously is incorrect—gait disturbance precedes the other symptoms and should prompt immediate evaluation 1, 3.
Question 2: Imaging Findings in NPH
Which MRI finding has the HIGHEST positive predictive value for shunt responsiveness in idiopathic NPH?
A) Evans index >0.3
B) Callosal angle <90 degrees
C) Elevated aqueductal CSF stroke volume on phase-contrast MRI
D) Periventricular white matter hyperintensities
E) Temporal horn enlargement
Correct Answer: C
Explanation: Elevated aqueductal CSF stroke volume measured by phase-contrast MRI demonstrates 100% positive predictive value for shunt responsiveness in published studies 4. This quantitative measurement of hyperdynamic CSF flow through the aqueduct over a cardiac cycle is superior to static anatomical findings 4. While the Evans index >0.3 (maximal width of frontal horns/maximal width of inner skull) is required for diagnosis of probable NPH, it does not predict shunt response 5. The callosal angle <90 degrees and temporal horn enlargement are supportive diagnostic features but lack the predictive accuracy of phase-contrast flow measurements 5. The cerebral aqueduct flow void on conventional MRI was historically associated with excellent shunt response (P < 0.003), but modern phase-contrast quantification provides superior predictive value 4.
Question 3: Diagnostic Workup for Suspected NPH
A 68-year-old presents with gait instability, mild cognitive slowing, and urinary urgency. CT shows ventriculomegaly. What is the MOST appropriate initial imaging study according to current guidelines?
A) CT head with IV contrast
B) MRI head without IV contrast
C) FDG-PET/CT brain
D) DTPA cisternography
E) MR spectroscopy
Correct Answer: B
Explanation: MRI head without IV contrast is the preferred initial imaging modality for NPH diagnosis 5, 1. The American College of Radiology designates MRI and CT without contrast as equivalent alternatives for initial imaging, but MRI is superior for detecting key diagnostic features 5. MRI can identify ventriculomegaly, narrowed posterior callosal angle, effaced sulci along high convexities, widened sylvian fissures, periventricular white matter changes, and the critical cerebral aqueduct flow void—findings that CT cannot reliably detect 5, 1. CT cannot visualize the aqueduct flow void and may miss small obstructing lesions that would indicate noncommunicating hydrocephalus 5. IV contrast is not indicated for NPH evaluation 5. FDG-PET/CT and DTPA cisternography are second-line tests that may help stratify shunt candidates but are not appropriate for initial diagnosis 5.
Question 4: Predictive Testing for Shunt Responsiveness
Which diagnostic test provides the MOST reliable prediction of clinical improvement following ventriculoperitoneal shunt placement?
A) Opening pressure >250 mm H2O on lumbar puncture
B) Clinical improvement after large-volume lumbar puncture (tap test)
C) Delayed clearance on DTPA cisternography
D) Evans index >0.35
E) Presence of complete clinical triad
Correct Answer: B
Explanation: Clinical improvement following large-volume lumbar puncture (tap test) or prolonged external lumbar drainage reliably identifies patients likely to respond to shunt surgery, with properly selected patients having an 80-90% chance of responding 6. The tap test involves removing sufficient CSF to assess gait and cognitive function before and after drainage 6. Clinical response to prolonged CSF drainage predicted shunt outcome in 100% of cases in published series 7. While the complete clinical triad suggests NPH, its presence alone does not predict shunt responsiveness 7. DTPA cisternography findings do not correlate sufficiently with shunt outcomes to justify proceeding with surgery based on cisternography alone 5. Opening pressure measurements are typically normal in NPH (hence "normal pressure"), and elevated pressures suggest alternative diagnoses 5. The degree of ventriculomegaly (Evans index) is required for diagnosis but does not predict treatment response 7.
Question 5: Hydrocephalus in Infectious Meningitis
A patient with coccidioidal meningitis develops acute hydrocephalus with opening pressure of 280 mm H2O. What is the MOST appropriate initial management?
A) Immediate ventriculoperitoneal shunt placement
B) Medical therapy with azole antifungals and repeated lumbar punctures
C) External ventricular drain placement
D) Endoscopic third ventriculostomy
E) Observation with serial imaging
Correct Answer: B
Explanation: For patients with increased intracranial pressure ≥250 mm H2O at diagnosis, initial management should consist of medical therapy with azole antifungals and repeated lumbar punctures 5. The pressure should be lowered by removing CSF in sufficient volume to reduce pressure to 50% of opening pressure or 200 mm H2O, whichever is greater, repeated at least daily for 4 days until pressure stabilizes to <250 mm H2O 5. However, because most patients with increased ICP will not resolve without permanent shunt placement, early MRI and neurosurgical consultation are strongly recommended 5. Hydrocephalus is the most common complication of CNS coccidioidal infection, occurring in approximately 40% of patients 5. Immediate shunt placement without attempting medical management and CSF drainage is premature, as some cases may respond to conservative measures 5. Observation alone is inappropriate when pressure exceeds 250 mm H2O, as this defines the need for urgent intervention 5.
Question 6: NPH in Young and Middle-Aged Adults
A 42-year-old reports 5 years of progressive gait difficulty, cognitive slowing affecting job performance, and urinary urgency. Examination shows only subtle gait changes, normal MMSE, and no incontinence. MRI reveals ventriculomegaly. What is the MOST likely diagnosis?
A) Multiple sclerosis
B) Early-onset Alzheimer disease
C) Syndrome of hydrocephalus in young and middle-aged adults (SHYMA)
D) Frontotemporal dementia
E) Conversion disorder
Correct Answer: C
Explanation: This presentation is characteristic of SHYMA, a clinically distinct syndrome comprising hydrocephalus of all etiologies in patients aged 16-55 years, characterized by prominent symptoms with subtle or absent clinical signs 2. In a series of 46 patients, 70% complained of gait problems, 70% had cognitive complaints, 48% had urinary urgency, and 84% reported impaired job performance 2. The hallmark of SHYMA is the discrepancy between symptom severity and examination subtlety—only 42.9% had minor gait changes on exam, 14.3% had mildly abnormal MMSE, and only 3.6% had frank incontinence 2. Despite subtle clinical signs, CSF diversion treatment is highly effective, with 93% showing symptomatic improvement (56% complete resolution, 37% partial resolution) at 16±11 months after shunting 2. Patients had been followed for an average of 6 years (range 1-30 years) before diagnosis, highlighting the importance of recognizing this syndrome 2. The combination of ventriculomegaly on imaging with this symptom pattern should prompt evaluation for hydrocephalus rather than dismissing symptoms due to normal examination findings 2.
Question 7: Radiographic Criteria for Probable NPH
Which combination of MRI findings is REQUIRED for diagnosing "probable" idiopathic NPH according to evidence-based guidelines?
A) Evans index >0.3 + callosal angle <90° + temporal horn enlargement
B) Ventricular enlargement not attributable to atrophy + no macroscopic CSF obstruction + at least one supportive feature
C) Periventricular white matter changes + aqueductal flow void + sulcal effacement
D) Ventriculomegaly + cortical atrophy + transependymal edema
E) Evans index >0.35 + complete clinical triad + elevated opening pressure
Correct Answer: B
Explanation: Evidence-based guidelines for probable INPH require: (1) ventricular enlargement not entirely attributable to cerebral atrophy or congenital enlargement (Evans index >0.3), (2) no macroscopic obstruction of CSF flow, and (3) at least one of the following: enlargement of temporal horns, callosal angle <90°, evidence of altered brain water content, or aqueductal/fourth ventricle flow void on MRI 5. These three criteria must all be present for "probable" INPH designation 5. Additional supportive findings include prior MRI showing smaller ventricles or cine MRI demonstrating increased ventricular flow rate, but these are not required for probable INPH 5. The presence of significant cortical atrophy would argue against NPH and suggest alternative neurodegenerative disease 5. Opening pressure is typically normal in NPH, and elevated pressure suggests alternative diagnoses 5. All diagnostic findings are optimally visualized on noncontrast MRI; IV contrast is not needed 5.
Question 8: Shunt Outcomes and Complications
What is the approximate rate of significant clinical improvement and serious complication rate in properly selected NPH patients undergoing ventriculoperitoneal shunt placement?
A) 29% improvement, 6% serious complications
B) 59% improvement, 38% any complications
C) 80-90% improvement, 6% serious complications
D) 50% improvement, 22% serious complications
E) 100% improvement, 5% serious complications
Correct Answer: C
Explanation: Properly selected patients using contemporary diagnostic tests (tap test, external lumbar drainage, or CSF infusion testing) have an 80-90% chance of responding to shunt surgery, with all symptoms potentially improving 6. This represents a substantial improvement over historical series that reported only 29% prolonged improvement (range 24-100%) with 6% combined rate of permanent neurological deficit and death 7. The discrepancy reflects improved patient selection using physiologically-based predictive tests rather than clinical and CT criteria alone 6, 7. Historical series reported complications in 38% of patients (range 5-100%) and need for additional surgery in 22% (range 0-47%), but these included minor complications and were based on less rigorous selection criteria 7. With modern programmable shunts and proper patient selection, the benefit-to-risk ratio is highly favorable 6. The key to achieving these superior outcomes is using tap test or prolonged external lumbar drainage to identify shunt-responsive patients before surgery 6, 7.
Question 9: Distinguishing NPH from Other Dementias
Which imaging modality is LEAST useful for differentiating idiopathic NPH from other causes of dementia?
A) MRI head without contrast showing structural features
B) Phase-contrast MRI measuring aqueductal CSF flow
C) MR spectroscopy measuring NAA/Cho ratios
D) FDG-PET/CT showing dorsal striatal hypometabolism
E) Conventional MRI showing aqueductal flow void
Correct Answer: C
Explanation: MR spectroscopy is not useful for differentiating NPH from other dementias and does not correlate with CSF diversion outcomes 5. While NAA/Cho and NAA/Cr ratios are significantly reduced in NPH patients compared to healthy controls, MR spectroscopy cannot reliably distinguish NPH from other dementias 5. Furthermore, MR spectroscopy findings do not predict shunt response 5. In contrast, structural MRI features (ventriculomegaly, callosal angle, temporal horn enlargement, periventricular changes) are diagnostic for NPH 5, 1. Phase-contrast MRI measuring elevated aqueductal CSF stroke volume has 100% positive predictive value for shunt responsiveness 4. FDG-PET/CT can demonstrate dorsal striatal hypometabolism with preserved cortical metabolism, helping distinguish NPH from other dementias, and may identify comorbid neurodegenerative disease 5. The aqueductal flow void on conventional MRI correlates with shunt response 4. MR spectroscopy should not be used for initial imaging of suspected NPH 5.
Question 10: Clinical Examination Findings in NPH
A patient with suspected NPH undergoes neurological examination. Which finding is MOST characteristic of the gait disturbance in NPH?
A) Steppage gait with foot drop
B) Ataxic wide-based gait with truncal instability
C) Hypokinetic gait with feet appearing "glued to the floor"
D) Spastic scissoring gait
E) Antalgic gait favoring one side
Correct Answer: C
Explanation: The cardinal sign of NPH is a hypokinetic gait disorder where the feet appear "glued to the floor" or "magnetic" 3. This gait disturbance is the most important clinical feature and typically appears first in the disease course 1, 3. The gait abnormality occurs in approximately 70% of NPH patients and is often the presenting symptom 2. Unlike other neurological conditions, there is often a striking discrepancy between the severity of gait complaints and the subtlety of examination findings—patients may report severe disability while examination shows only minor gait changes 2. This is particularly true in younger patients with SHYMA, where only 42.9% had detectable gait abnormalities on examination despite 70% complaining of gait problems 2. Steppage gait suggests peripheral neuropathy or peroneal nerve palsy, ataxic gait suggests cerebellar pathology, spastic scissoring suggests upper motor neuron lesions, and antalgic gait suggests orthopedic pathology—none of these patterns are characteristic of NPH 3.