431 lines
31 KiB
Markdown
431 lines
31 KiB
Markdown
---
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title: "Aqueductal Stenosis"
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docid: "6dfa6261-3945-4606-850b-51484d05e70c"
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authors:
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- key: "2c9d2e67-05db-4d26-b8cb-02e0f7566179"
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value: "Usha D. Nagaraj, MD"
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- key: "b2e6dabb-ee1c-42a4-a332-9f0814c1c607"
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value: "Surjith Vattoth, MD, FRCR"
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breadcrumbs:
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-
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name: "Brain"
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slug: "brain"
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treeNodeId: "6d8829f1-14d7-45af-8675-255189aa526a"
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "51c00394-446e-4a38-94af-d3b1d14d34e8"
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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: "529d3e33-f508-498c-bc70-cf962e81e629"
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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: "33b267f0-908c-4c77-81f8-f6135d1bc592"
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name: "Hydrocephalus"
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slug: "hydrocephalus"
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treeNodeId: "9ce86e3b-fab6-4657-9e51-5f47bb1a51b5"
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-
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name: "Aqueductal Stenosis"
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slug: "aqueductal-stenosis"
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treeNodeId: null
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category: "Brain"
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cmeTopicId: "22225b65-7fc8-4415-b55f-20fb85f6ecf5"
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documentVersionId: "f14f3356-bf6d-4b97-a2e5-77751c20492b"
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imageCount: 15
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lastUpdated: "07/16/20"
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pageDescription: "Aqueductal Stenosis"
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pageKeywords: "Brain, Diagnosis, Anatomy-Based Diagnoses, Ventricles and Cisterns, Hydrocephalus, Aqueductal Stenosis"
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pageTitle: "Aqueductal Stenosis | STATdx"
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enhancedTitle: "Aqueductal Stenosis"
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type: "DX"
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references: true
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breadcrumbs:
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- "Brain"
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- "Diagnosis"
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- "Anatomy-Based Diagnoses"
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- "Ventricles and Cisterns"
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- "Hydrocephalus"
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- "Aqueductal Stenosis"
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---
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# KEY FACTS
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- ## Terminology
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- Aqueductal stenosis (AS)
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- ## Imaging
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- Ventriculomegaly of lateral and 3rd ventricles with normal-sized 4th ventricle
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- Obstruction of cerebral aqueduct ± tectal thickening
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- Macrocephaly in fetus and infant
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- Multiplanar MR with sagittal 3D True FISP/bFFE sequence to evaluate aqueduct
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- ## Top Differential Diagnoses
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- Supratentorial volume loss
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- Benign enlargement of subarachnoid fluid spaces of infancy
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- Communicating hydrocephalus
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- Secondary obstructive hydrocephalus
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- ## Pathology
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- Congenital AS is common cause of fetal hydrocephalus
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- Can be acquired (isolated) or associated with genetic disorder
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- Subsets include stenosis from tectal thickening, obstructing web/gliotic tissue, or forking
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- ## Clinical Issues
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- Though may present at any time from birth to adulthood, bimodal distribution in 1st year of life and adolescence
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- Headache, papilledema, 6th nerve palsy, macrocephaly, bulging fontanelle
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- C-section may be required for prenatally diagnosed cases due to macrocephaly
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- ## Diagnostic Checklist
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- Look for coexisting brain anomalies, such as rhombencephalosynapsis or diencephalic-mesencephalic dysplasia
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# TERMINOLOGY
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- ## Abbreviations
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- Aqueductal stenosis (AS)
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- ## Definitions
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- Ventriculomegaly involving lateral and 3rd ventricles as result of complete or partial obstruction to CSF flow within cerebral aqueduct
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- AS diagnosis generally refers to congenital form characterized by varying degree of obstruction at level of cerebral aqueduct
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- However, tumors, germinal matrix hemorrhage, or vascular lesions can obstruct aqueduct as well
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Ventriculomegaly of lateral and 3rd ventricles with normal-sized 4th ventricle
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- Macrocephaly (typical of AS) can help differentiate from supratentorial volume loss (usually normal or decreased head circumference)
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- ### Location
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- Cerebral aqueduct
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- Most commonly at superior colliculi or intercollicular sulcus level
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- ### Size
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- Normal mean aqueductal cross-sectional area at birth is 0.2-1.8 mm²
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- ### Morphology
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- Funnel-shaped enlargement of proximal cerebral aqueduct or diffuse ↓ caliber of entire aqueduct
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- ## CT Findings
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- ### NECT
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- Ventriculomegaly of lateral and 3rd ventricles, normal-sized 4th ventricle
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- ± periventricular interstitial edema from uncompensated hydrocephalus
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- ## MR Findings
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- ### T1WI
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- Ventriculomegaly of lateral and 3rd ventricles, foramina of Monro
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- Corpus callosum (CC) thinned, stretched upward
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- Often limits evaluation for coexisting callosal dysgenesis
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- ± lateral ventricular diverticulum (a.k.a. ventricular rupture or dehiscence)
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- Extraaxial CSF effacement
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- Limits ability to evaluate gyral-sulcal pattern
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- Normal size of 4th ventricle, basilar foramina
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- Aqueductal web: Thin tissue membrane separating dilated aqueduct from normal-sized 4th ventricle
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- Look for coexisting brain anomalies, such as rhombencephalosynapsis or diencephalic-mesencephalic dysplasia (incomplete segmentation between diencephalon and mesencephalon)
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- ### T2WI
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- Presence of dephasing jet or flow void through aqueduct may suggest that AS is less likely, though does not completely exclude diagnosis
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- ± periventricular interstitial edema
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- Tectal plate thickening
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- Loss of differentiation between superior and inferior colliculi
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- May be difficult to differentiate from tectal plate glioma in certain cases
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- AS should **not** have T2-/FLAIR hyperintense signal or enhancement in tectal plate (tectum should be isointense to rest of midbrain on all pulse sequences)
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- Unlikely to be tectal plate glioma < 3 years of age
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- Septum pellucidum often absent secondary to perforation
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- ### T2* GRE
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- May have trace amounts of blood products in aqueduct and ventricular system but no frank germinal matrix hemorrhage or other cause for bleeding
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- ### T1WI C+
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- Presence of tumor enhancement excludes congenital AS
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- Hydrocephalus may induce leptomeningeal venous stasis → mimics meningitis or CSF metastases
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- ### MRA
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- Upward displacement of anterior cerebral artery branches secondary to hydrocephalus
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- ### MRV
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- Downward displacement of internal cerebral veins secondary to hydrocephalus
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- ### MR cine
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- Phase-contrast imaging may demonstrate absent or diminished CSF flow in aqueduct
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- ## Ultrasonographic Findings
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- ### Grayscale ultrasound
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- Ventriculomegaly of lateral and 3rd ventricles with normal-sized 4th ventricle in newborn with macrocephaly is highly suggestive of AS
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- Obstetrical ultrasound may permit prenatal diagnosis
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- Usually severe lateral ventriculomegaly (> 15 mm)
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- Decreased transverse cerebellar diameter with coexisting rhombencephalosynapsis; fetal MR can help confirm
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- Adducted thumbs in male fetus raise possibility of X-linked hydrocephalus
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- ## Imaging Recommendations
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- ### Best imaging tool
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- Multiplanar MR with sagittal 3D True FISP/bFFE sequence to evaluate aqueduct
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# DIFFERENTIAL DIAGNOSIS
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- ## Supratentorial Volume Loss
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- Should have normal or decreased head circumference
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- ## Benign Enlargement of Subarachnoid Spaces in Infancy
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- a.k.a "benign macrocrania," thought to be mild form of communicating hydrocephalus from immaturity of CSF absorption mechanisms
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- Patients have normal neurologic exam
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- Ventricles are normal in size or mildly enlarged
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- ## Communicating Hydrocephalus
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- Secondary to impaired absorption of CSF in subarachnoid spaces rather than anatomic obstruction
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- Causes include meningitis, leptomeningeal metastatic disease, venous hypertension
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- ## Secondary Obstructive Hydrocephalus
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- Cause of obstruction is extrinsic to aqueduct: Tumor, germinal matrix hemorrhage, vascular lesion, etc.
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- AS
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- Aqueductal lumen normally decreases in size beginning in 2nd month of fetal life and continuing until birth
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- Normal mean cross-sectional area of aqueduct is 0.5 mm² (range: 0.2-1.8 mm²)
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- Narrowing caused by growth pressures upon aqueduct from adjacent mesencephalic structures
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- AS pathologically obstructs CSF flow into 4th ventricle
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- CSF production in choroid plexus continues → lateral/3rd ventricular fluid ↑ pressure, ventriculomegaly
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- Ventricles expand, compress adjacent parenchyma, stretch CC
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- May rupture/open ependymal cell junctions → periventricular edema, ventricular diverticulum
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- May be acquired or genetic
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- Isolated acquired forms from prior injury/insult, such as trace hemorrhage or infection, which results in webs or gliotic tissue obstructing aqueduct
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- Genetic forms often have other associated anomalies
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- ### Genetics
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- X-linked hydrocephalus
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- One of most common inherited causes of AS
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- Caused by mutation of *L1CAM*gene
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- Gene located on X chromosome (Xq28)
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- *L1CAM* expression is essential during normal embryonic development of nervous system
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- Codes for neural cell adhesion molecule transmembrane glycoprotein in immunoglobulin superfamily of cell adhesion molecules
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- Site of mutation within L1 protein correlates with disease severity
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- Patients have poor prognosis despite early shunting
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- Associated syndromes
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- MASA syndrome: **Mental disability**, **a**phasia, **s**huffling gait, and **a**dducted thumbs
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- CRASH syndrome: **C**allosal hypoplasia, mental disability, **a**dducted thumbs, **s**pastic paraplegia, and X-linked **h**ydrocephalus
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- ### Associated abnormalities
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- Rhombencephalosynapsis
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- Up to 65% of patients with rhombencephalosynapsis have coexisting AS
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- CRASH syndrome
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- Absence/diminution of corticospinal tracts, thalamic fusion, collicular fusion, absence of septum pellucidum, CC dysgenesis
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- Thin cerebral mantle, malformations of cortical development, hypoplastic white matter
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- Dystroglycanopathy (a.k.a. congenital muscular dystrophies, such as Walker-Warburg)
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- Usually associated with cerebellar dysplasia and abnormally small brainstem
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- Chiari 2 malformation
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- Not well described, but coexisting AS suspected in cases with increased head circumference (majority of Chiari 2 patients have decreased head circumference)
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- ## Microscopic Features
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- Can have associated malformations of cortical development with poor differentiation and maturation of cortical neurons on histology
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- Aqueductal fork shows branching of aqueduct into dorsal and ventral channels
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- Dorsal channel usually divided into several ductules
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- These channels cannot be resolved on imaging due to microscopic size
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Symptoms depend upon patient age at time of diagnosis
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- Onset can be insidious, may occur from birth to adulthood though typically bimodal distribution
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- ### Other signs/symptoms
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- Headache, papilledema, 6th nerve palsy, bulging fontanelles
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- Macrocrania, especially if sutures open
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- Parinaud syndrome
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- Sun-setting eyes
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- Lid retraction
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- Tonic downgaze
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- Bobble-head doll syndrome (rare)
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- ## Demographics
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- ### Age
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- Presentation, 2 peaks of distribution: 1 in 1st year of life (more common), other in adolescence
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- ### Sex
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- M:F = 2:1
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- ### Epidemiology
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- 0.5-1 per 1,000 births, recurrence rate of 1-4.5% in siblings
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- AS responsible for ~ 20% of congenital hydrocephalus
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- Most common cause of prenatal obstructive hydrocephalus
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- ## Natural History & Prognosis
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- Hydrocephalus usually progressive unless treated
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- May stabilize as "arrested" or compensated hydrocephalus
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- While isolated congenital AS has much better prognosis than AS with genetic disorder or other brain anomalies, only ~ 1/3 of patients with isolated AS have normal neurodevelopmental outcomes
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- ## Treatment
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- CSF shunt diversion
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- Endoscopic 3rd ventriculostomy
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- Cerebral aqueductoplasty for membranous and short-segment aqueductal stenoses (selected cases)
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- Prenatally diagnosed cases may require C-section due to macrocephaly
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Look for coexisting brain anomalies as they make difference in prognosis
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- ## Image Interpretation Pearls
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- Use thin-section 3D True FISP/bFFE to better delineate aqueduct
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51b0f452-75a6-4416-baed-960891a1f404
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## References
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# Selected References
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1. [Guo D et al: A novel nonsense mutation in the L1CAM gene responsible for X-linked congenital hydrocephalus. J Gene Med. e3180, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=32128973%5Bpmid%5D)
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1. [Alhousseini A et al: Familial hydrocephalus and dysgenesis of the corpus callosum associated with Xp22.33 duplication and stenosis of the aqueduct of sylvius with X-linked recessive inheritance pattern. Gynecol Obstet Invest. 84(4):412-6, 2019](http://www.ncbi.nlm.nih.gov/pubmed/?term=30965333%5Bpmid%5D)
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1. [Heaphy-Henault KJ et al: Congenital aqueductal stenosis: findings at fetal mri that accurately predict a postnatal diagnosis. AJNR Am J Neuroradiol. 39(5):942-9, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29519789%5Bpmid%5D)
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1. [Kline-Fath BM et al: Congenital aqueduct stenosis: progressive brain findings in utero to birth in the presence of severe hydrocephalus. Prenat Diagn. 38(9):706-12, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29927492%5Bpmid%5D)
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1. [Tonetti DA et al: Clinical outcomes of isolated congenital aqueductal stenosis. World Neurosurg. 114:e976-81, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29588243%5Bpmid%5D)
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1. [Yamada S et al: Current and emerging MR imaging techniques for the diagnosis and management of CSF flow disorders: a review of phase-contrast and time-spatial labeling inversion pulse. AJNR Am J Neuroradiol. 36(4):623-30, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25012672%5Bpmid%5D)
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1. [Griessenauer CJ et al: Pediatric tectal plate gliomas: clinical and radiological progression, MR imaging characteristics, and management of hydrocephalus. J Neurosurg Pediatr. 13(1):13-20, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24180680%5Bpmid%5D)
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1. [Kartal MG et al: Evaluation of hydrocephalus and other cerebrospinal fluid disorders with MRI: an update. Insights Imaging. 5(4):531-41, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24903254%5Bpmid%5D)
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1. [Tully HM et al: Infantile hydrocephalus: a review of epidemiology, classification and causes. Eur J Med Genet. 57(8):359-68, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24932902%5Bpmid%5D)
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1. [Ucar M et al: Evaluation of aqueductal patency in patients with hydrocephalus: three-dimensional high-sampling-efficiency technique (SPACE) versus two-dimensional turbo spin echo at 3 Tesla. Korean J Radiol. 15(6):827-35, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=25469096%5Bpmid%5D)
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1. [Whitehead MT et al: Rhombencephalosynapsis as a cause of aqueductal stenosis: an under-recognized association in hydrocephalic children. Pediatr Radiol. 44(7):849-56, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24633306%5Bpmid%5D)
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1. [Muehlmann M et al: Magnetic resonance-based estimation of intracranial pressure correlates with ventriculoperitoneal shunt valve opening pressure setting in children with hydrocephalus. Invest Radiol. 48(7):543-7, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23695081%5Bpmid%5D)
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1. [O'Neill BR et al: Rapid sequence magnetic resonance imaging in the assessment of children with hydrocephalus. World Neurosurg. 80(6):e307-12, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23111234%5Bpmid%5D)
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1. [Rush ET et al: Four new patients with Gomez-Lopez-Hernandez syndrome and proposed diagnostic criteria. Am J Med Genet A. 161A(2):320-6, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23292994%5Bpmid%5D)
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1. [Gallo P et al: The endoscopic trans-fourth ventricle aqueductoplasty and stent placement for the treatment of trapped fourth ventricle: long-term results in a series of 18 consecutive patients. Neurol India. 60(3):271-7, 2012](http://www.ncbi.nlm.nih.gov/pubmed/?term=22824682%5Bpmid%5D)
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1. [Ishak GE et al: Rhombencephalosynapsis: a hindbrain malformation associated with incomplete separation of midbrain and forebrain, hydrocephalus and a broad spectrum of severity. Brain. 135(Pt 5):1370-86, 2012](http://www.ncbi.nlm.nih.gov/pubmed/?term=22451504%5Bpmid%5D)
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1. [Schroeder C et al: Why does endoscopic aqueductoplasty fail so frequently? Analysis of cerebrospinal fluid flow after endoscopic third ventriculostomy and aqueductoplasty using cine phase-contrast magnetic resonance imaging. J Neurosurg. 117(1):141-9, 2012](http://www.ncbi.nlm.nih.gov/pubmed/?term=-1%5Bpmid%5D)
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1. [Cinalli G et al: Hydrocephalus in aqueductal stenosis. Childs Nerv Syst. 27(10):1621-42, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=21928028%5Bpmid%5D)
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1. [Algin O et al: Phase-contrast MRI and 3D-CISS versus contrast-enhanced MR cisternography on the evaluation of the aqueductal stenosis. Neuroradiology. 52(2):99-108, 2010](http://www.ncbi.nlm.nih.gov/pubmed/?term=19756563%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. [Bateman GA: Magnetic resonance imaging quantification of compliance and collateral flow in late-onset idiopathic aqueductal stenosis: venous pathophysiology revisited. J Neurosurg. 107(5):951-8, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=17977266%5Bpmid%5D)
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1. [da Silva LR et al: Endoscopic aqueductoplasty in the treatment of aqueductal stenosis. Childs Nerv Syst. 23(11):1263-8, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=17676325%5Bpmid%5D)
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1. [Koch-Wiewrodt D et al: Success and failure of endoscopic third ventriculostomy in young infants: are there different age distributions?. Childs Nerv Syst. 22(12):1537-41, 2006](http://www.ncbi.nlm.nih.gov/pubmed/?term=16944172%5Bpmid%5D)
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1. [Sansone JM et al: Endoscopic cerebral aqueductoplasty: a trans-fourth ventricle approach. J Neurosurg. 103(5 Suppl):388-92, 2005](http://www.ncbi.nlm.nih.gov/pubmed/?term=16302609%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. [Tisell M et al: Neurological symptoms and signs in adult aqueductal stenosis. Acta Neurol Scand. 107(5):311-7, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12713521%5Bpmid%5D)
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1. [Fukuhara T et al: Clinical features of late-onset idiopathic aqueductal stenosis. Surg Neurol. 55(3):132-6; discussion 136-7, 2001](http://www.ncbi.nlm.nih.gov/pubmed/?term=11311904%5Bpmid%5D)
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1. [Partington MD: Congenital hydrocephalus. Neurosurg Clin N Am. 12(4):737-42, ix, 2001](http://www.ncbi.nlm.nih.gov/pubmed/?term=11524294%5Bpmid%5D)
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1. [Schroeder HW et al: Endoscopic aqueductoplasty: technique and results. Neurosurgery. 45(3):508-15; discussion 515-8, 1999](http://www.ncbi.nlm.nih.gov/pubmed/?term=10493373%5Bpmid%5D)
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1. [Graf WD et al: The pachygyria-polymicrogyria spectrum of cortical dysplasia in X-linked hydrocephalus. Eur J Pediatr Surg. 8 Suppl 1:10-4, 1998](http://www.ncbi.nlm.nih.gov/pubmed/?term=9926316%5Bpmid%5D)
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1. [Castro-Gago M et al: Autosomal recessive hydrocephalus with aqueductal stenosis. Childs Nerv Syst. 12(4):188-91, 1996](http://www.ncbi.nlm.nih.gov/pubmed/?term=8739404%5Bpmid%5D)
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1. [Kadowaki C et al: Cine magnetic resonance imaging of aqueductal stenosis. Childs Nerv Syst. 11(2):107-11, 1995](http://www.ncbi.nlm.nih.gov/pubmed/?term=7758008%5Bpmid%5D)
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1. [Villani R et al: Long-term outcome in aqueductal stenosis. Childs Nerv Syst. 11(3):180-5, 1995](http://www.ncbi.nlm.nih.gov/pubmed/?term=7773981%5Bpmid%5D)
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## Images
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### Selected Images
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*Sagittal graphic shows obstructive hydrocephalus with markedly enlarged lateral and 3rd ventricles, a stretched (thinned) corpus callosum, and a funnel-shaped cerebral aqueduct <img src='img/arrows/BS.png'/> related to distal obstruction. Note the normal size of the 4th ventricle and depression of the floor of the 3rd ventricle <img src='img/arrows/BC.png'/> from the hydrocephalus.*
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*Sagittal T2WI from a fetal MR at 25 weeks gestational age with aqueductal stenosis shows macrocephaly, lateral and 3rd ventriculomegaly, and no CSF in the cerebral aqueduct <img src='img/arrows/CS.png'/>.*
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*Sagittal T1WI MR depicts proximal aqueductal stenosis <img src='img/arrows/WS.png'/> producing enlargement of the lateral and 3rd ventricles with depression of the fornices <img src='img/arrows/WC.png'/> in conjunction with normal 4th ventricle size. The tectum is dysplastic and thickened with collicular fusion <img src='img/arrows/WO.png'/>.*
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*Sagittal FIESTA of a 5 year old with aqueductal stenosis secondary to a small obstructing web <img src='img/arrows/CS.png'/> is shown. This patient underwent a 3rd ventriculostomy <img src='img/arrows/CC.png'/> and is doing well. There are no other brain anomalies.*
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*Sagittal T2WI MR of a 5 day old with prenatal diagnosis of aqueductal stenosis demonstrates effacement of the cerebral aqueduct <img src='img/arrows/CS.png'/> with thickening of the tectum <img src='img/arrows/CC.png'/>.*
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*Axial T1WI MR in the same patient demonstrates rhombencephalosynapsis <img src='img/arrows/WS.png'/> and bilateral choanal atresia <img src='img/arrows/BS.png'/>. Other anomalies in this patient included bilateral microphthalmia and tracheoesophageal fistula. This patient had a partial deletion of chromosome 3q and SOX2 gene mutation.*
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*Sagittal T1WI MR in a 2 day old with aqueductal stenosis with effacement of the aqueduct <img src='img/arrows/CS.png'/> is shown. This patient also has diencephalic-mesencephalic dysplasia with incomplete separation of an enlarged massa intermedia from the midbrain <img src='img/arrows/WO.png'/> with thickening of the 3rd ventricular floor <img src='img/arrows/WS.png'/>.*
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*Axial T2WI MR in the same patient demonstrates dilation of the lateral and 3rd ventricles with right ventricular diverticulum <img src='img/arrows/CS.png'/> and multiple subependymal gray matter heterotopias <img src='img/arrows/WS.png'/>.*
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*Sagittal T1WI MR in a patient with Walker-Warburg syndrome shows severe tectal dysgenesis <img src='img/arrows/WS.png'/> with aqueductal occlusion. Marked enlargement of the lateral ventricles more than the 3rd ventricle is present. A "zigzag" brainstem and very small cerebellum are characteristic of this syndrome.*
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*Coronal T2WI MR in the same patient confirms marked ventriculomegaly, funnel-shaped cerebral aqueductal stenosis <img src='img/arrows/WS.png'/>, fused fornices <img src='img/arrows/BS.png'/>, and classic cobblestone lissencephaly.*
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### Additional Images
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*Coronal T2WI MR of the same neonate, on the 1st day of life, shows marked ventriculomegaly with asymmetric bilateral subdural hygromas following spontaneous ventricular decompression into the bilateral subdural spaces. This patient also has the additional midline congenital anomaly of rhombencephalosynapsis with characteristic incomplete dentate gyrus separation <img src='img/arrows/BS.png'/> correlating with clinical truncal ataxia.*
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*Sagittal T2WI MR of a neonate with severe congenital hydrocephalus, imaged on the 1st day of life, shows severe aqueductal stenosis <img src='img/arrows/CS.png'/> and abnormal dysplastic tectal thickening <img src='img/arrows/CO.png'/>. Severe congenital hydrocephalus has resulted in spontaneous decompression into the subdural spaces <img src='img/arrows/BS.png'/>.*
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*Coronal T2WI MR shows "funneling" of the aqueduct in the coronal plane <img src='img/arrows/CS.png'/>, with a markedly distended ventricular system proximal to the stenotic aqueduct.*
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*Sagittal T2WI MR shows massively distended 3rd and lateral ventricles with distal aqueductal stenosis <img src='img/arrows/BS.png'/>. Note the severe stretching of the corpus callosum <img src='img/arrows/BO.png'/> and depression of the fornices <img src='img/arrows/BC.png'/>.*
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*Sagittal T2WI MR reveals distal aqueductal stenosis with an enlarged, funnel-shaped cerebral aqueduct <img src='img/arrows/CS.png'/> and mild abnormal tectal thickening. Note the lateral and 3rd ventriculomegaly with normal size of the 4th ventricle.*
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