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KEY FACTS

Terminology
- Hydrocephalus (HCP) - Enlargement of cerebral ventricles secondary to abnormal CSF formation, flow, or absorption resulting in ↑ CSF volume
Imaging
- Shunt failure → dilated ventricles + edema around ventricles, along catheter and reservoir
- Use CT or MR to evaluate ventricle size, plain radiograph shunt series to identify mechanical shunt failure
- Baseline CT/MR following shunt insertion, follow-up at 1 year and as clinically needed
- Shunt radionuclide studies: Used to confirm distal obstruction
Top Differential Diagnoses
- Shunt failure with normal ventricle size or lack of interstitial edema
- Noncompliant (slit) ventricle syndrome
- Acquired Chiari 1 malformation/tonsillar ectopia
Pathology
- Obstructive HCP: Secondary to physical blockage by tumor, adhesions, cyst
- Communicating HCP: Secondary to ↓ CSF absorption across arachnoid granulations
Clinical Issues
- Older children/adults: Headache, vomiting, lethargy, seizure, neurocognitive symptoms
- Infants: Bulging fontanelle, ↑ head circumference, irritability, lethargy
Diagnostic Checklist
- Shunt + headache not always shunt failure
- Confirm programmable shunt valve setting after MR
- Compare current CT with prior studies to detect subtle changes in ventricle size

TERMINOLOGY

Abbreviations
- Shunt types: Ventriculoperitoneal (VP), ventriculoatrial (VA), ventriculopleural (VPL), lumboperitoneal (LP)
Definitions
- Ventriculomegaly - General term for enlargement of cerebral ventricles
- Hydrocephalus (HCP) - Enlargement of cerebral ventricles secondary to abnormal CSF formation, flow, or absorption resulting in ↑ CSF volume - Subset of ventriculomegaly - Onset over days (acute), weeks (subacute), or months to years (chronic)

IMAGING

General Features

Best diagnostic clue

- Shunt failure: Dilated ventricles + edema ("blurring") around ventricles and along catheter, reservoir

Location

- VP shunt common; VA and VPL used rarely unless VP contraindicated

Size

- Ventricular size is relative → ventriculomegaly, may indicate shunt failure in one patient and be stable finding in another
        - Change in ventricular size in individual patient probably significant
        - Conversely, some patients manifest shunt failure with minimal to no change in ventricular size
- Distal catheter must be sized long enough to permit somatic growth, prevent retraction out of abdomen or chest

Morphology

- Shunt system components
        - Proximal catheter in ventricles, subarachnoid space, syrinx cavity, or thecal sac
        - Unidirectional valve prevents reflux into ventricles
        - Reservoir used to sample CSF, acutely relieve pressure
        - Distal catheter tunneled through subcutaneous tissues → tip in peritoneal cavity, cardiac atrium, or pleural cavity

Radiographic Findings

Radiography

- Evaluate shunt catheter system integrity
        - Shunt fracture, separation, migration
        - Distal catheter may retract out of abdomen if significant somatic growth since shunt placement

Fluoroscopic Findings
- Contrast shuntogram to define site of obstruction (historical interest)

CT Findings

NECT

- Ventricular dilatation (diffuse or loculated)
        - Isolated ventricle after infection, hemorrhage → interventricular synechia
        - Periventricular interstitial edema ("blurred" ventricle margins) → acute HCP
- Small, slit ventricles → noncompliant ventricle syndrome, chronic overdrainage
- ± subdural hematoma (CSF overdrainage)

CECT

- ± ependymal enhancement (chemical or infectious ventriculitis)
- Detection of intracranial abscess or empyema as complication of shunt infection

MR Findings

T1WI

- Assess ventricular size, characterize brain anatomy

T2WI

- ± interstitial periventricular edema → acute shunt failure

FLAIR

- Interstitial edema more conspicuous than on T1WI or T2WI

T2* GRE

- Assess hemorrhagic shunt tracts, interventricular hemorrhage

DWI

- ↑ diffusivity with interstitial edema

T1WI C+

- ± enhancement with ventriculitis, abscess, neoplasm
- Pachymeningeal enhancement due to low intracranial pressure (ICP)

MRA

- Stretched, displaced arteries around dilated ventricles secondary to ventriculomegaly

MRV

- Venous thrombosis may precede HCP or follow shunting
        - Leads to ↑ intraventricular/ICP

MR cine

- Evaluate patency of normal CSF pathways, 3rd ventriculostomy

MRS

- Small lactate resonances detected in CSF of up to 20% of HCP, even if HCP absent

Ultrasonographic Findings

Grayscale ultrasound

- Useful in neonates for serial assessment of ventricular size (requires open fontanelle)

Pulsed Doppler

- Resistive indices increase with shunt obstruction, ↑ ICP

Color Doppler

- Research studies document flow within shunt tubing, aqueduct

Nonvascular Interventions
- Interventricular contrast injection through shunt + NECT→ detect ventricular isolation needing additional catheter
Nuclear Medicine Findings
- PET
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- Cerebral vascular reserve (CVR) measurement may aid selection of shunt candidates
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- Shunt radionuclide studies - Radiotracer injected into shunt reservoir; serial imaging to document timing of radiotracer egress from distal catheter tip - Used to confirm distal obstruction

Imaging Recommendations

Best imaging tool

- Brain NECT to assess for acute ventricular size change
- Fast MR protocols (HASTE, SSFSE) used in many centers with 24-hour MR availability to avoid cumulative radiation exposure

Protocol advice

- Brain CT or MR to evaluate ventricle size
- Baseline CT/MR following shunt insertion, follow-up at 1 year and as clinically needed
- Plain film shunt series to identify mechanical shunt fracture or disconnection

DIFFERENTIAL DIAGNOSIS

Shunt Failure With Normal Ventricle Size or Lack of Interstitial Edema
- Look for fluid along shunt catheter or reservoir as only sign of malfunction
- May require diagnosis on clinical grounds
Noncompliant (Slit) Ventricle Syndrome
- Usually older child (shunted in infancy)
- Small ventricles + intermittent signs of shunt obstruction
- Ventricles normal/small, even if shunt malfunctioning
- May be caused by shunt-induced sutural ossification or poor ventricular compliance
Acquired Chiari 1 Malformation/Tonsillar Ectopia
- Functioning LP shunt produces tonsillar descent through foramen magnum
- More common with valveless systems
- Not always symptomatic

PATHOLOGY

General Features

Etiology

- Normal CSF production = 0.2-0.7 mL/minute; 250 (child) to 500 mL (adult) per 24-hour period
        - Majority of CSF produced by choroid plexus, resorbed by arachnoid granulations
        - Capacity of ventricles in healthy adult = 25 mL
        - Total CSF volume (adult) = 125 mL
- Impairment of CSF circulation
        - Obstructive
                  - Usually at narrowest points in CSF circulation (aqueduct, foramina of Monro)
                  - Tumor, web/synechia, congenital aqueductal stenosis
        - Inadequate reabsorption across arachnoid granulations into venous sinuses
                  - Arachnoid granulations "clogged" after hemorrhage, inflammation
                  - Diminished pressure gradient from subarachnoid space to venous sinuses secondary to venous hypertension
                  - Impaired CSF absorption → CSF accumulation, ↑ ICP
- CSF shunt establishes accessory drainage pathway to bypass obstructed natural CSF flow pathways
        - Restores or maintains normal ICP
- Each shunt, valve, device carries its own set of complications
        - All types → material degradation/fatigue, mechanical stress (especially craniocervical junction, inferior ribs)
        - VP → abdominal complications (CSF pseudocyst, ascites, bowel perforation)
        - VPL → symptomatic pleural effusion
        - VA → shunt nephritis, cor pulmonale, pulmonary embolus
        - LP → arachnoiditis, cerebellar tonsillar herniation, high catheter migration rate
        - Programmable shunt → unintentional reprogram during MR
        - Shuntless CSF diversion → 3rd ventriculostomy, 4th ventricle outlet fenestration
        - Silicone allergy → allergic response, catheter occlusion with debris
        - Antisiphon devices → obstruction by capsule formation
        - 1-piece shunt → ↓ catheter obstruction rate, ↑ slit ventricle/subdural hemorrhage rate
        - Flanged catheters → ↑ incidence of proximal occlusion
        - Internal 3rd ventricle to spinal SAS (Lapras catheter) → no external access, no method to check flow
        - Flow vs. pressure regulation
                  - Pressure-regulating shunts prone to overdrainage
                  - Flow-regulating valves prone to obstruction
                  - Magnetic valves commonly used but cause artifact on MR and require resetting after MR
- Cerebral atrophy, focal destructive lesions also produce ↑ CSF spaces, but these are not HCP
        - Loss of cerebral tissue → vacant space passively filled with CSF
        - Not result of hydrodynamic disorder → not HCP

Associated abnormalities

- Shunts placed with CSF blood/protein > 1 g/dL prone to early blockage, failure
- Shunt infection
- Ventricular loculation or isolation
- Overshunting

Gross Pathologic & Surgical Features
- Ventricular ependymal adhesions (scar)
- Extracranial shunt tubing calcification
Microscopic Features
- Gliosis along intracranial shunt tract

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Children, adults
        - Headache, vomiting, lethargy, seizure
        - Neuropsychologic, cognitive, or behavioral
- Infants
        - Bulging fontanelle, ↑ head circumference, irritability, lethargy

Clinical profile

- Depends on underlying clinical diagnosis necessitating CSF diversion, number of previous shunts, complications

Demographics

Age

- 1st weeks of life for myelomeningocele, congenital HCP
- Older age at 1st shunting for HCP following trauma, meningitis, tumor

Epidemiology

- 160,000 shunts implanted each year worldwide
- CSF shunts in USA ~ 125,000 total
        - 33,000 placed per year (~ 45-50% revisions)

Natural History & Prognosis
- After shunting, 70% either normal or relatively normal intelligence (if no complications or associated anomalies)
- Epilepsy incidence up to 47% if shunt follows meningitis, hemorrhage
- HCP mortality depends on shunt complication: Malfunction (30%), infection (20%), pulmonary embolus (7%)
- Acute shunt obstruction in shunt-dependent patients may lead to death
- Majority of shunt revisions occur during first 6 months after shunt placement - Age at time of shunt surgery, previous shunt surgery, etiology of HCP, and HCP type independently associated with incidence of shunt revision - 50% of patients need multiple revisions, progressively shorter time interval to next failure
Treatment
- Shunt revision - Replace intraventricular component/valve for proximal obstruction - Alter valve pressure setting/type if over- or underdraining - Programmable shunt valves permit transcutaneous adjustment of pressure setting - Lengthen distal shunt as child grows
- 3rd ventriculostomy to avoid indwelling shunt if blockage is distal to 3rd ventricle
- Subtemporal decompression or 3rd ventriculostomy for noncompliant ventricle syndrome
- Laparoscopic or open abdominal procedure for distal obstruction related to CSF pseudocyst

DIAGNOSTIC CHECKLIST

Consider
- Shunt + headache does not always mean shunt failure - Consider sinusitis, trauma, sinovenous thrombosis, viral infection
- Confirm programmable shunt valve setting after MR
- Plain film shunt series has extremely low yield in absence of clinical evidence for mechanical shunt failure
Image Interpretation Pearls
- Compare with prior studies to detect subtle ventricular size changes
- Poor ventricular compliance may prevent change in ventricular size despite florid clinical shunt failure
- Fluid tracking along shunt may be only sign of failure; possible even if ventricles normal or unchanged size

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References

Selected References

Images

Selected Images

Lateral skull radiograph of acute ventriculoperitoneal (VP) shunt failure from a plain radiograph shunt series demonstrates a mechanical shunt catheter disconnection between the programmable valve and the reservoir.

Axial bone CT in the same patient reveals the mechanical catheter disconnection between the reservoir and the programmable shunt valve. This finding had not appeared on the most recent comparison CT scan (not shown).

AP radiograph from a shunt series demonstrates intracardiac migration of the VP shunt catheter with the tip residing in the right interlobar pulmonary artery.

AP radiograph of the pelvis in a 4 year old with a VP shunt who presented with left scrotal swelling demonstrates a coiled distal shunt catheter in the left scrotum. The migration of the catheter to the scrotum is due to a patent processus vaginalis.

Axial NECT depicts symmetric interstitial edema within the periventricular white matter. Ventricular size is significantly larger than demonstrated on a prior CT (not shown), supporting the diagnosis of acute shunt failure.

Axial NECT in a patient with VP shunt who presented with severe headaches shows collapsed lateral ventricles . Slit ventricle syndrome presents as severe headaches due to noncompliant ventricles and should not be confused with radiologic slit ventricles.

$Coronal bone CT demonstrates fracture or disconnection of the ventricular catheter from the reservoir resulting in clinical shunt failure (larger ventricles on NECT).$ Coronal bone CT demonstrates fracture or disconnection of the ventricular catheter from the reservoir resulting in clinical shunt failure (larger ventricles on NECT).

Axial NECT following bilateral ventricular catheter placement in a patient with severe hydrocephalus (HCP) and brain atrophy reveals development of a large left subdural hematoma following VP shunting.

Axial NECT in a patient with HCP presenting with distal VP shunt failure shows the peritoneal catheter tip within a loculated pelvic fluid collection (CSF pseudocyst ).

Frontal cisternogram-radionuclide shuntogram examination performed after injecting the shunt valve reservoir reveals no spillage from the distal catheter after 10 minutes. Further delayed imaging (not shown) confirmed absence of spillage from the catheter, substantiating distal shunt obstruction.

Additional Images

Lateral radiograph from a plain film shunt series in an infant with acute shunt failure demonstrates that the ventricular catheter has pulled out of the head and is lying along the distal catheter within the scalp (tip ).

AP radiograph in a patient with chest pain after ventriculopleural (VPL) shunt placement depicts a right pneumothorax related to the shunt placement. Note the abandoned catheter fragment from a prior VP shunt system.

AP radiography indicates a large left pleural effusion in a symptomatic child with a left VPL shunt catheter .

Axial CECT of the pelvis in a shunted patient with HCP presenting with acute shunt failure, fever, and abdominal pain shows the peritoneal VP shunt catheter residing within a rim-enhancing pelvic fluid collection that represents a pelvic abscess secondary to perforated appendicitis.

Axial NECT in a patient with HCP presenting with shunt failure shows the peritoneal VP shunt catheter tip residing within a large loculated pelvic fluid collection (CSF pseudocyst).

Axial T2 MR depicts reservoir , shunt tubing , collapsed left lateral ventricle, and dilated isolated right lateral ventricle with associated interstitial transependymal edema .

Axial NECT in a patient with posthemorrhagic HCP following contrast injection through the right ventricular catheter shows contrast within the isolated right ventricle but no contrast transit into either the left lateral or 3rd ventricle .

Axial FLAIR MR shows the sequelae of CSF overdrainage leading to bilateral subdural hematomas and ventricular collapse following shunt placement.

Axial NECT of the brain shows development of bilateral subdural hematohygromata following shunting of severe obstructive HCP.

Sagittal T1 C+ MR of a patient with intracranial hypotension shows obliteration of the suprasellar cistern, sagging fat midbrain with a closed angle between peduncles/pons , dural enhancement, and tonsillar descent.

$AP radiography in patient with a VP shunt and acute shunt failure reveals fractured shunt tubing .$ AP radiography in patient with a VP shunt and acute shunt failure reveals fractured shunt tubing .

AP radiography shows a disconnected and caudally migrated peritoneal shunt catheter fragment looped within the pelvis.

AP radiography shows knotted abdominal shunt tubing. The tightly coiled appearance suggests an abnormal extraperitoneal placement of the shunt. Two shunts are present due to isolated ventricles.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Abbreviations

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

Radiographic Findings

Radiography

Fluoroscopic Findings

CT Findings

NECT

CECT

MR Findings

T1WI

T2WI

FLAIR

T2* GRE

DWI

T1WI C+

MRA

MRV

MR cine

MRS

Ultrasonographic Findings

Grayscale ultrasound

Pulsed Doppler

Color Doppler

Nonvascular Interventions

Nuclear Medicine Findings

PET

Imaging Recommendations

Best imaging tool

Protocol advice

DIFFERENTIAL DIAGNOSIS

Shunt Failure With Normal Ventricle Size or Lack of Interstitial Edema

Noncompliant (Slit) Ventricle Syndrome

Acquired Chiari 1 Malformation/Tonsillar Ectopia

PATHOLOGY

General Features

Etiology

Associated abnormalities

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Clinical profile

Demographics

Age

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Images

Selected Images

Additional Images

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