481 lines
35 KiB
Markdown
481 lines
35 KiB
Markdown
---
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title: "Hydrocephalus"
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docid: "e9481739-278e-4682-ab1e-4326a77c3d0c"
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authors:
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- key: "838e1722-2479-4fbd-a5fe-d965980a1a2c"
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value: "Blaise V. Jones, MD"
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breadcrumbs:
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-
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name: "Pediatrics"
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slug: "pediatrics"
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treeNodeId: "a915965c-d436-44cf-ae65-2f22e7246ea4"
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-
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "2b5cea64-a083-489e-ac0c-ec14ba059026"
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-
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name: "Pediatric Neuroradiology"
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slug: "pediatric-neuroradiology"
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treeNodeId: "d0eb8f4a-e769-43dd-896c-8c9c27ce8759"
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-
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name: "Brain"
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slug: "brain"
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treeNodeId: "feaaadba-649b-4f0a-9aad-9188a8f9926a"
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-
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name: "Anatomy-Based Diagnoses"
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slug: "anatomy-based-diagnoses"
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treeNodeId: "0c0853dc-8217-425b-86d1-2d958e17f1f9"
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-
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name: "Ventricles and Cisterns"
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slug: "ventricles-and-cisterns"
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treeNodeId: "8b535c75-9cd3-445e-a4c7-345b2e444f03"
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-
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name: "Hydrocephalus"
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slug: "hydrocephalus"
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treeNodeId: null
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category: "Pediatrics"
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cmeTopicId: "bddbd7cd-39c8-4b51-98d3-3e314108c4d1"
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documentVersionId: "47d2ee1e-6049-4ddc-8280-fc06e5d281da"
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imageCount: 25
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lastUpdated: "02/06/24"
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pageDescription: "Hydrocephalus"
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pageKeywords: "Pediatrics, Diagnosis, Pediatric Neuroradiology, Brain, Anatomy-Based Diagnoses, Ventricles and Cisterns, Hydrocephalus"
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pageTitle: "Hydrocephalus | STATdx"
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enhancedTitle: "Hydrocephalus"
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type: "DX"
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references: true
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breadcrumbs:
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- "Pediatrics"
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- "Diagnosis"
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- "Pediatric Neuroradiology"
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- "Brain"
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- "Anatomy-Based Diagnoses"
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- "Ventricles and Cisterns"
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- "Hydrocephalus"
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---
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# KEY FACTS
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- ## Terminology
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- Ventriculomegaly caused by
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- Obstruction of CSF egress from ventricles: Intraventricular obstructive hydrocephalus
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- Decreased CSF resorption from subarachnoid space: Extraventricular obstructive hydrocephalus
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- Increased CSF production
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- Use FOHR to track ventricle size over time
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- (Transverse diameter of frontal horns + transverse diameter of occipital horns) ÷ 2x transverse diameter of cranium
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- ## Imaging
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- 3D FIESTA/CISS
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- Acquire in sagittal plane to outline aqueduct
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- Limited shunt MR protocol
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- 30-second acquisition in each plane
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- Useful substitute for CT
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- Insensitive for parenchymal abnormalities
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- ## Pathology
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- Extracellular, extravascular fluid in brain is managed by glymphatic system
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- CSF circulates from within ventricles → subarachnoid space → perivascular spaces ↔ interstitium ↔ perivenular spaces → subarachnoid space
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- CSF is resorbed from subarachnoid space at multiple sites
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- Along sheaths of cranial nerves (especially olfactory bulb) into head and neck lymphatics
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- Along sheaths of spinal nerves into perispinal lymphatics
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- Into meningeal (dural) lymphatics
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- Into dural sinuses via arachnoid granulations
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- Previously thought to be major site of resorption
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- Hydrocephalus results from obstruction of CSF egress from ventricular system or reduced resorption from subarachnoid space
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# TERMINOLOGY
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- ## Abbreviations
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- Intraventricular obstructive hydrocephalus (IVOH)
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- Acute IVOH (aIVOH)
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- Chronic "compensated" IVOH (cIVOH)
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- Extraventricular obstructive hydrocephalus (EVOH)
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- Frontal occipital horn ratio (FOHR)
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- (Transverse diameter of frontal horns + transverse diameter of occipital horns) ÷ 2x transverse diameter of cranium
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- Subarachnoid lymphatic-like membrane (SLYM)
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- Recently discovered 4th meningeal membrane that divides subarachnoid space into inner and outer compartments
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- ## Definitions
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- Ventriculomegaly caused by
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- Obstruction of CSF egress from ventricles: IVOH
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- Decreased CSF resorption from subarachnoid space: EVOH
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- Increased CSF production
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- Ventriculomegaly secondary to loss of parenchyma, a.k.a. ex vacuo dilation, is **not**hydrocephalus
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Enlarged ventricles
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- With decreased extraaxial spaces (EAS): IVOH
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- With periventricular (transependymal) edema: Acute IVOH
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- With enlarged EAS: EVOH
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- ### Size
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- FOHR > 0.33
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- Temporal horn width > 3 mm
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- ### Morphology
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- Ventricles proximal to obstruction enlarge, appear more rounded
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- Trigones and occipital horns typically enlarge most
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- Wall pressure is proportional to diameter: Laplace law
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- Optic and infundibular recesses of 3rd ventricle may preferentially enlarge
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- Optic nerve sheaths may enlarge → papilledema
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- ## CT Findings
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- ### NECT
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- Large ventricles proximal to obstruction
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- aIVOH
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- "Ballooned" ventricles with periventricular low-density "halo"
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- cIVOH
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- "Ballooned" ventricles, periventricular "halo"
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- Basal cisterns, sulci compressed/obliterated
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- ## MR Findings
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- ### T1WI
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- Lateral ventricles enlarged
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- Corpus callosum (CC) thinned, stretched upward
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- May be impinged against falx
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- Impaction may cause pressure necrosis
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- Fornix, internal cerebral veins (ICV) displaced downward
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- Enlarged 3rd ventricle often herniated into expanded sella
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- Funnel-shaped aqueduct of Sylvius in aqueductal stenosis
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- ### T2WI
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- Acute obstruction
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- Transependymal edema extends into periventricular white matter (WM)
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- Accentuated around frontal and occipital horns
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- Chronic obstruction
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- Large ventricles without transependymal edema
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- CC may show hyperintensity after decompression (15% of shunted IVOH cases)
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- ### T1WI C+
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- Diffuse leptomeningeal disease can cause EVOH
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- May only be apparent on postcontrast imaging
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- ### MRS
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- Small lactate resonances can be detected in up to 20% of CSF spaces, even if no hydrocephalus
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- ## Other Modality Findings
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- Contrast-enhanced ventriculography
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- MR/CT used to identify site of obstruction, status of 3rd ventriculostomies
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- MR can be used for assessing CSF flow
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- Cardiac-gated phase-contrast MR
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- May show loss of CSF flow through aqueduct
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- Useful for assessing status of endoscopic 3rd ventriculostomy (ETV)
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- ## Imaging Recommendations
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- ### Best imaging tool
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- Sagittal T2WI MR
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- Administer contrast if pattern suggests EVOH and no etiology is apparent
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- ### Protocol advice
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- 3D FIESTA/CISS
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- Acquire in sagittal plane to outline aqueduct
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- Decreases CSF flow artifact
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- Allows better delineation of ventricular contour, septa
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- SWI to assess for superficial siderosis in posthemorrhagic hydrocephalus
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- Limited shunt MR protocol
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- Single-shot rapid technique with heavy T2 weighting
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- 30-second acquisition in each plane
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- Useful substitute for CT
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- Reduce radiation exposure in frequently imaged population
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- Rapid aquisition reduces need for sedation
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- Insensitive for parenchymal abnormalities
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- Use FOHR to track ventricle size over time
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- Especially in younger children with open sutures
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- Accounts for increase in head circumference with increase in ventricular size
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# DIFFERENTIAL DIAGNOSIS
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- ## Ventricular Enlargement Secondary to Parenchymal Loss
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- a.k.a. ex vacuo ventriculomegaly
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- Age related (ventricular volume increases 1.2-1.4 mL after 60 years)
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- Ischemia/infarction, trauma, infection, toxic
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- Obtuse frontal angle (> 110°)
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- Associated enlargement of sulci, cisterns
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- Normal lateral ventricles can be asymmetric
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- ## Benign Enlargement of Subarachnoid Spaces and Ventricles
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- a.k.a. benign macrocrania
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- Seen in association with macrocephaly in infants
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- Transient and self-limited
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- Not associated with developmental delay
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- Does not require CSF diversion
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- Likely reflects relative immaturity of glymphatic system
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- Diminished ability to resorb CSF as interstitial fluid compartment is shrunk by progressive myelination
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Extracellular, extravascular fluid in brain is managed by glymphatic system
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- Maintains homeostatic balance between interstitial fluid compartment, cellular compartment, and intravascular compartment
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- Analogous to lymphatic system in other organs
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- While brain parenchyma does not have lymphatic vessels, they are present in dura mater and along sheaths of cranial nerves
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- CSF circulates from within ventricles → subarachnoid space → perivascular spaces ↔ interstitium ↔ perivenular spaces → subarachnoid space
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- CSF is resorbed from subarachnoid space at multiple sites
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- Along sheaths of cranial nerves (especially olfactory bulb) into head and neck lymphatics
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- Along sheaths of spinal nerves into perispinal lymphatics
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- Into meningeal (dural) lymphatics
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- Into dural sinuses via arachnoid granulations
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- Previously thought to be major site of resorption
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- SLYM is thought to facilitate CSF flow
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- Disruption after trauma may explain reduced glymphatic flow and posttraumatic cerebral edema
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- Normal CSF production = 0.2-0.35 mL/min
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- Capacity of lateral, 3rd ventricles in adult = 20 mL
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- Total volume of CSF in adult = 120 mL
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- Hydrocephalus results from obstruction of CSF egress from ventricular system or reduced resorption from subarachnoid space
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- Obstruction within ventricular system results in IVOH
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- Ventricles expand, compress adjacent parenchyma; stretching may rupture/open ependymal cell junctions
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- Periventricular interstitial fluid increases → myelin destruction
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- Etiology depends on site
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- Foramen of Monro
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- Colloid cyst
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- Subependymal giant cell astrocytoma in tuberous sclerosis
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- 3rd ventricle
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- Craniopharyngioma, hypothalamic glioma, arachnoid cyst
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- Aqueduct of Sylvius
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- Aqueductal stenosis, tectal glioma, pineal region tumor
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- Obstruction by hemorrhage or inflammatory debris
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- Enlarged vein of Galen due to arteriovenous fistula
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- 4th ventricle
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- Medulloblastoma, ependymoma, pilocytic astrocytoma
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- Chiari, Dandy-Walker malformation, Blake pouch cyst
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- Metastasis, neurocysticercosis, or meningioma can occur at multiple intraventricular locations
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- Reduced resorption from subarachnoid space results in EVOH
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- Subarachnoid pathology may reduce absorptive capacity
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- Hemorrhage or inflammation (acute or chronic)
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- Metabolic disorders may reduce resorptive capacity
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- Overproduction of CSF may overwhelm ability of glymphatic system to manage and resorb CSF
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- Choroid plexus papilloma or carcinoma
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- Focally enlarged and hyperenhancing choroidal mass
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- Choroid plexus villous hyperplasia
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- Diffusely enlarged choroid
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- ### Genetics
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- Cell adhesion molecule L1 (*L1CAM*) recognized as cause of X-linked aqueductal stenosis
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- Located on X chromosome (Xq28)
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- ## Gross Pathologic & Surgical Features
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- Focal/generalized ventricular enlargement
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- Ependyma, adjacent WM are secondarily injured
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- Variable pathology depending on causative factor
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Headache, papilledema (aIVOH)
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- Nausea, vomiting
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- Diplopia
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- 6th nerve palsy caused by compression of cisternal segment
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- ### Clinical profile
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- Varies with etiology, severity, age of onset
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- ## Demographics
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- ### Age
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- May be any age from in utero (congenital hydrocephalus) to adult
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- ### Epidemiology
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- Epidemiological data varies widely, depending upon etiology and type of hydrocephalus
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- ## Natural History & Prognosis
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- Usually progressive unless treated
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- ## Treatment
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- Obstructive hydrocephalus is managed surgically
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- CSF diversion (shunt or ETV)
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- Resection of obstructing or hypersecreting lesion
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- Most common neurosurgical procedure in children = CSF shunting for hydrocephalus
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- CSF diversion is typically delayed in EVOH
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- Tendency to be much more shunt dependent
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- Less tolerant of minor pressure changes
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- Lesser degree of ventriculomegaly increases difficulty of surgery
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Longstanding aqueductal stenosis can be caused by slow-growing tectal tumor
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- Compensated IVOH
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- CSF function and homeostasis are far more complex than previously thought
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- Free communication among anatomic/functional compartments is necessary for proper brain health
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- ## Image Interpretation Pearls
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- Size of ventricles generally correlates poorly with intracranial pressure
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- Pulsatile CSF may create confusing signal intensity, even mimic intraventricular mass
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cf76a2a7-da6e-419b-9e56-481a10e5b803
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## References
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# Selected References
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1. [Møllgård K et al: A mesothelium divides the subarachnoid space into functional compartments. Science. 379(6627):84-8, 2023](http://www.ncbi.nlm.nih.gov/pubmed/?term=36603070%5Bpmid%5D)
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1. [Krishnan P et al: Neuroimaging in pediatric hydrocephalus. Indian J Pediatr. 86(10):952-60, 2019](http://www.ncbi.nlm.nih.gov/pubmed/?term=31077004%5Bpmid%5D)
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1. [Ha SK et al: Magnetic resonance imaging and histopathological visualization of human dural lymphatic vessels. Bio Protoc. 8(8), 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29780855%5Bpmid%5D)
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1. [Patel SK et al: Advanced neuroimaging techniques in pediatric hydrocephalus. Pediatr Neurosurg. 52(6):436-45, 2017](http://www.ncbi.nlm.nih.gov/pubmed/?term=28095378%5Bpmid%5D)
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1. [Algin O et al: Assessment of third ventriculostomy patency with the 3D-SPACE technique: a preliminary multicenter research study. J Neurosurg. 122(6):1347-55, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25859808%5Bpmid%5D)
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1. [Jessen NA et al: The glymphatic system: a beginner's guide. Neurochem Res. 40(12):2583-99, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25947369%5Bpmid%5D)
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1. [Russo N et al: Endoscopic approaches to intraventricular lesions. J Neurol Surg A Cent Eur Neurosurg. 76(5):353-60, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=26008954%5Bpmid%5D)
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1. [Flannery AM et al: Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 1: introduction and methodology. J Neurosurg Pediatr. 14 Suppl 1:3-7, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=25988777%5Bpmid%5D)
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1. [Mazzola CA et al: Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 2: management of posthemorrhagic hydrocephalus in premature infants. J Neurosurg Pediatr. 14 Suppl 1:8-23, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=25988778%5Bpmid%5D)
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1. [Nikas DC et al: Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 10: change in ventricle size as a measurement of effective treatment of hydrocephalus. J Neurosurg Pediatr. 14 Suppl 1:77-81, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=25988786%5Bpmid%5D)
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1. [Dinçer A et al: Radiologic evaluation of pediatric hydrocephalus. Childs Nerv Syst. 27(10):1543-62, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=21928020%5Bpmid%5D)
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1. [Mirone G et al: Hydrocephalus and spinal cord tumors: a review. Childs Nerv Syst. 27(10):1741-9, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=21928038%5Bpmid%5D)
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1. [Oi S: Classification of hydrocephalus: critical analysis of classification categories and advantages of "Multi-categorical Hydrocephalus Classification" (Mc HC). Childs Nerv Syst. 27(10):1523-33, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=21928018%5Bpmid%5D)
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1. [Dinçer A et al: Is all "communicating" hydrocephalus really communicating? Prospective study on the value of 3D-constructive interference in steady state sequence at 3T. AJNR Am J Neuroradiol. 30(10):1898-906, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=19643921%5Bpmid%5D)
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1. [Feng F et al: Evaluation of radionuclide cerebrospinal fluid scintigraphy as a guide in the management of patients with hydrocephalus. Clin Imaging. 33(2):85-9, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=19237049%5Bpmid%5D)
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1. [Linninger AA et al: Normal and hydrocephalic brain dynamics: the role of reduced cerebrospinal fluid reabsorption in ventricular enlargement. Ann Biomed Eng. 37(7):1434-47, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=19373558%5Bpmid%5D)
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1. [Oertel JM et al: Endoscopic third ventriculostomy in obstructive hydrocephalus due to giant basilar artery aneurysm. J Neurosurg. 110(1):14-8, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=18991498%5Bpmid%5D)
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1. [Stoquart-El Sankari S et al: Phase-contrast MR imaging support for the diagnosis of aqueductal stenosis. AJNR Am J Neuroradiol. 30(1):209-14, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=18832663%5Bpmid%5D)
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1. [Sekula RF Jr et al: A case of an elderly adult presenting with obstructive hydrocephalus secondary to a rare hemorrhagic suprasellar pilocytic astrocytoma. Clin Neuropathol. 27(6):396-9, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=19130737%5Bpmid%5D)
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1. [Yamada S et al: Visualization of cerebrospinal fluid movement with spin labeling at MR imaging: preliminary results in normal and pathophysiologic conditions. Radiology. 249(2):644-52, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=18936318%5Bpmid%5D)
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1. [Erdogan AR et al: Sex and handedness differences in size of cerebral ventricles of normal subjects. Int J Neurosci. 114(1):67-73, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=14660068%5Bpmid%5D)
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1. [Gaser C et al: Ventricular enlargement in schizophrenia related to volume reduction of the thalamus, striatum, and superior temporal cortex. Am J Psychiatry. 161(1):154-6, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=14702264%5Bpmid%5D)
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1. [Wyldes M et al: Isolated mild fetal ventriculomegaly. Arch Dis Child Fetal Neonatal Ed. 89(1):F9-13, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=14711845%5Bpmid%5D)
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1. [Akhondi H et al: Hydrocephalus as a presenting manifestation of neurosarcoidosis. South Med J. 96(4):403-6, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12916562%5Bpmid%5D)
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1. [Bhattacharyya KB et al: Bobble-head doll syndrome: some atypical features with a new lesion and review of the literature. Acta Neurol Scand. 108(3):216-20, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12911467%5Bpmid%5D)
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1. Brown KP et al: 1H MRS in human hydrocephalus. J MRI. 14:291-9, 2003
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1. [Grunert P et al: The role of third ventriculostomy in the management of obstructive hydrocephalus. Minim Invasive Neurosurg. 46(1):16-21, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12640578%5Bpmid%5D)
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1. [Joseph VB et al: MR ventriculography for the study of CSF flow. AJNR Am J Neuroradiol. 24(3):373-81, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12637285%5Bpmid%5D)
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1. [Sener RN: Callosal changes in obstructive hydrocephalus: observations with FLAIR imaging, and diffusion MRI. Comput Med Imaging Graph. 26(5):333-7, 2002](http://www.ncbi.nlm.nih.gov/pubmed/?term=12204238%5Bpmid%5D)
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## Images
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### Selected Images
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*Depiction of normal CSF flow through the glymphatic system. CSF descends along periarterial perivascular spaces (PVS) and through the interstitium before exiting along perivenular PVS, clearing macromolecules (black particles). The exchange between interstitium and PVS is modulated by astrocytic endfeet expressing AQP4 (pink channels).*
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*Depiction of normal CSF flow through the glymphatic system. CSF descends along periarterial perivascular spaces (PVS) and through the interstitium before exiting along perivenular PVS, clearing macromolecules (black particles). The exchange between interstitium and PVS is modulated by astrocytic endfeet expressing AQP4 (pink channels).*
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*An isoattenuating colloid cyst <img src='img/arrows/WC.png'/> obstructs the foramina of Monro in this 7-year-old, causing obstructive hydrocephalus.*
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*A large suprasellar arachnoid cyst balloons upward <img src='img/arrows/BS.png'/> and obstructs the foramina of Monro in this 1-year-old with macrocrania.*
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*This 3-month-old with hydrocephalus has a Blake pouch cyst obstructing outflow of CSF from the 4th ventricle. Note the membrane across the posterior foramen magnum <img src='img/arrows/CC.png'/> and the uplifting of the vermis <img src='img/arrows/CO.png'/>.*
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*A medulloblastoma <img src='img/arrows/WO.png'/> fills and obstructs the 4th ventricle in this 10-year-old, leading to supratentorial ventriculomegaly and papilledema <img src='img/arrows/BS.png'/>. Papilledema visible on MR typically correlates to grade 3 on the Frisen scale (moderate edema).*
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*Axial FLAIR MR through the lateral ventricles in the same child shows transependymal edema capping the frontal and occipital horns <img src='img/arrows/WO.png'/>, reflecting the increased pressure in the ventricular system.*
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*Bacterial meningitis (group A Streptococcus in this example) can restrict resorption of CSF but can also obstruct at the cerebral aqueduct and 4th ventricular outlets when complicated by ventriculitis, evident on this image by abnormal enhancement of the ependyma <img src='img/arrows/WO.png'/>.*
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*An infiltrating tectal glioma <img src='img/arrows/WS.png'/> obstructs the cerebral aqueduct in this 10-year-old. Absence of transependymal edema suggests a compensated hydrocephalus.*
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*A papilloma of the choroid plexus in the occipital horn of the left lateral ventricle <img src='img/arrows/WS.png'/> causes moderate hydrocephalus by excessive CSF production in this 2-month-old.*
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*CSF overproduction can rarely be nonneoplastic in nature, as in this 6-month-old with villous hyperplasia of the choroid plexus in each lateral ventricle <img src='img/arrows/BS.png'/>. Note the preservation of peripheral sulci, as the unfused sutures of the infant can widen in response to increased intracranial volume.*
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### Additional Images
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*Sagittal T1 MR shows a large mass within the 4th ventricle <img src='img/arrows/BO.png'/> causing intraventricular obstructive hydrocephalus or noncommunicating hydrocephalus.*
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*Sagittal T2 MR in the same patient shows transependymal CSF flow, seen here as "fingers" extending into white matter around the enlarged lateral ventricle. The case was medulloblastoma with acute IVOH.*
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*Coronal T1 C+ MR shows IVOH with a large, enhancing intraventricular mass <img src='img/arrows/BS.png'/> causing marked enlargement of the lateral ventricles <img src='img/arrows/WS.png'/>.*
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*Axial NECT in the same patient shows the large intraventricular mass <img src='img/arrows/BS.png'/> within the 4th ventricle. Note the dilated temporal horns <img src='img/arrows/WS.png'/>.*
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*Sagittal T1 MR shows IVOH secondary to aqueductal stenosis and distal stenosis of cerebral aqueduct <img src='img/arrows/BC.png'/>. Note the enlarged lateral and 3rd ventricles.*
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*Axial FLAIR MR shows neurosarcoidosis and EVOH secondary to diffuse meningeal disease. Periventricular white matter hyperintensities <img src='img/arrows/BS.png'/> are also present, as well as choroid involvement <img src='img/arrows/WO.png'/>.*
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*Coronal T1 C+ MR shows neurocysticercosis involvement within the 3rd ventricle and aqueduct <img src='img/arrows/BS.png'/>, causing IVOH. The lateral ventricles are dilated.*
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*Axial FLAIR MR shows neurocysticercosis resulting in IVOH. Large intraventricular cysts are present in the lateral vents <img src='img/arrows/BS.png'/>, obstructing the foramina of Monro.*
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*Axial T1 MR shows a well-defined, hyperintense lesion <img src='img/arrows/BO.png'/> at the foramen of Monro in a patient with headaches, most consistent with a colloid cyst. Note the enlargement of the lateral ventricles <img src='img/arrows/BC.png'/> due to obstruction at the foramen of Monro.*
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*Sagittal T1 C+ MR shows a homogeneously enhancing mass in the posterior 3rd ventricle <img src='img/arrows/WO.png'/>, which causes obstruction and dilatation of the lateral and 3rd ventricles. On pathology, this was an astrocytoma.*
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*Coronal T2 MR shows a pilocytic astrocytoma centered in the right thalamus <img src='img/arrows/CO.png'/>, causing severe mass effect on the 3rd ventricle <img src='img/arrows/CS.png'/> and resultant obstructive hydrocephalus <img src='img/arrows/WC.png'/>.*
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*Axial T2 MR demonstrates a well-defined CSF intensity cyst with the left temporal horn most consistent with an ependymal cyst <img src='img/arrows/BO.png'/>. Note the dilated and trapped left temporal horn <img src='img/arrows/BS.png'/>.*
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*Sagittal T1 C+ MR shows an enhancing mass in the pineal region <img src='img/arrows/BS.png'/> causing mass effect on the tectal plate and aqueductal obstruction. Note the extensive leptomeningeal enhancement due to CSF spread of tumor. CSF cytology showed a primitive neuroectodermal tumor.*
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*A medulloblastoma <img src='img/arrows/WO.png'/> fills and obstructs the 4th ventricle in this 10-year-old, leading to supratentorial ventriculomegaly and papilledema.*
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*FIESTA shows pineal parenchymal tumor of intermediate differentiation <img src='img/arrows/WO.png'/> obstructing the cerebral aqueduct in this 8-year-old boy.*
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