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PubMed This is a summary of 14 peer-reviewed journal articles Updated
Neurology · Aqueductal Stenosis

Diagnosis and Imaging: How Doctors "See" the Blockage

At a Glance

To diagnose Aqueductal Stenosis, doctors use high-resolution MRI scans (like CISS or FIESTA) and CSF flow studies (CINE MRI) to locate the blockage. These precise images reveal whether the blockage is a thin membrane or a long narrowing, which determines the best surgical treatment.

Diagnosing Aqueductal Stenosis (AS) has evolved significantly with modern technology. While a standard MRI can show that the brain’s fluid chambers are enlarged, it often cannot see the tiny “clog” itself. To get a definitive answer, neurologists use specialized “high-definition” imaging that looks specifically at how fluid moves within the brain [1][2].

Understanding the specific terms and sequences used in these reports can help you advocate for a more precise diagnosis and treatment plan.

Key MRI Sequences: Seeing the “Clog”

A standard brain MRI is like looking at a road map; the sequences below are like using high-resolution satellite imagery and traffic flow sensors to see exactly where the accident is [3].

  • 3D-DRIVE, CISS, or FIESTA: These are “high-resolution” T2-weighted sequences. They are essential because they provide enough detail to see aqueductal webs or membranes—thin, tissue-paper-like blockages that are often invisible on a regular scan [1][4].
  • Phase-Contrast MRI (CINE): This is a “functional” scan. Instead of a still photo, it creates a movie of the cerebrospinal fluid (CSF) moving. If the scan shows no signal or a “void” where fluid should be flowing through the aqueduct, it confirms the blockage is complete [3][2].
  • Contrast-Enhanced MRI: This is used to make sure the blockage isn’t caused by a small vascular “birthmark” (like a DVA) or a tiny tumor that might be hidden without the use of a contrast dye [5][6].

Deciphering Your Radiology Report

Radiology reports use technical shorthand to describe how the brain is reacting to the extra fluid. Here are the terms you are most likely to see:

Term What it Means in Plain Language
Ventriculomegaly The brain’s fluid chambers (ventricles) are larger than normal. This is the primary sign of hydrocephalus [7].
Evans Index A ratio used to measure brain swelling. A score above 0.3 usually indicates that the ventricles are abnormally enlarged [8].
Aqueductal Funneling The top of the aqueduct looks wide and tapers to a point, like a funnel. This suggests fluid is being pushed against a blockage [9].
Transependymal Edema This is a “fuzzy” appearance around the ventricles, suggesting that fluid is under so much pressure it is leaking into the surrounding brain tissue [10].
Bowing of the Corpus Callosum The large bridge in the center of the brain is being pushed upward and arched by the fluid pressure beneath it [11].

Diagnosis in Infants

For babies, the process often starts before birth. Prenatal Ultrasound or Fetal MRI can identify enlarged ventricles and “funneling” of the aqueduct early on [9][12]. After birth, doctors may use Transcranial Ultrasonography—a painless scan through the baby’s soft spot—to monitor the size of the ventricles without needing repeated MRIs [13].

Why Precision Matters

The difference between a “long narrowing” of the tube and a “thin membrane” is important. A thin membrane might be treated with aqueductoplasty (using a tiny balloon to pop the membrane open), whereas a long narrowing is usually treated with an ETV (creating a new bypass entirely) [4][14]. Ensuring your imaging includes these high-resolution sequences is the best way to determine which surgical path is right for you.

Common questions in this guide

What is the Evans Index on my MRI report?
The Evans Index is a ratio used by radiologists to measure brain swelling. A score above 0.3 typically indicates that the brain's fluid chambers, or ventricles, are abnormally enlarged due to fluid buildup.
What is the best MRI to diagnose aqueductal stenosis?
High-resolution MRI sequences like 3D-DRIVE, CISS, or FIESTA are used to see thin membranes that cause blockages. Doctors also use Phase-Contrast (CINE) MRI, which creates a video of the fluid moving, to prove that flow is blocked at the aqueduct.
What does aqueductal funneling mean?
Aqueductal funneling means the top of the brain's fluid pathway looks wide but tapers to a point, like a funnel. This shape on an MRI suggests that cerebrospinal fluid is being pushed against a blockage.
What is transependymal edema?
Transependymal edema appears as a fuzzy area around the ventricles on an MRI scan. It suggests that cerebrospinal fluid is under so much pressure that it is leaking out of the ventricles and into the surrounding brain tissue.
How do doctors diagnose aqueductal stenosis in infants?
Diagnosis can begin before birth using prenatal ultrasound or fetal MRI to look for enlarged ventricles. After birth, doctors often use a painless transcranial ultrasound through the baby's soft spot to monitor the fluid chambers without needing repeated MRIs.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the 'Evans Index' on my/my child's most recent scan, and how has it changed over time?
  2. 2.Did the MRI include 'flow-sensitive' sequences (like Phase-Contrast/CINE) to prove that fluid is blocked at the aqueduct?
  3. 3.Are there any signs of 'transependymal edema' (fluid leaking into the brain tissue), which would suggest high pressure?
  4. 4.Based on the high-resolution images (CISS or FIESTA), is the blockage a long segment of narrowing or just a thin 'web' or 'membrane'?
  5. 5.Does the shape of the third ventricle floor look favorable for an ETV procedure?

Questions For You

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References

References (14)
  1. 1

    A Case of Aqueductal Stenosis with Bilateral Papilledema and Abducens Nerve Palsies without Headache.

    Nakata D, Okada H, Doi T, et al.

    Case reports in ophthalmology 2024; (15(1)):873-878 doi:10.1159/000542582.

    PMID: 39980535
  2. 2

    Phase-contrast and three-dimensional driven equilibrium (3D-DRIVE) sequences in the assessment of paediatric obstructive hydrocephalus.

    Mohammad SA, Osman NM, Khalil RM

    Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2018; (34(11)):2223-2231 doi:10.1007/s00381-018-3850-6.

    PMID: 29850941
  3. 3

    Three-Dimensional Constructive Interference in Steady State Sequences and Phase-Contrast Magnetic Resonance Imaging of Arrested Hydrocephalus.

    Elkafrawy F, Reda I, Elsirafy M, et al.

    World neurosurgery 2017; (98()):296-302 doi:10.1016/j.wneu.2016.10.140.

    PMID: 27826087
  4. 4

    Late-onset aqueductal membranous occlusion treated neuroendoscopic procedure and consideration of its pathological findings: A case report.

    Nakamura K, Kuge A, Yamaki T, et al.

    Surgical neurology international 2023; (14()):98 doi:10.25259/SNI_37_2023.

    PMID: 37025542
  5. 5

    Aqueductal developmental venous anomaly causing obstructive hydrocephalus: A case report and review of the literature.

    Hayashi T, Uchino A, Tokushige K, Baba Y

    Radiology case reports 2024; (19(5)):2024-2030 doi:10.1016/j.radcr.2024.02.023.

    PMID: 38449483
  6. 6

    Mesencephalic developmental venous anomaly causing obstructive hydrocephalus: illustrative case.

    Hiraga K, Hayashi S, Oshima R, et al.

    Journal of neurosurgery. Case lessons 2023; (5(12)).

    PMID: 36941200
  7. 7

    Hydrocephalus in children.

    Rekate HL, Blitz AM

    Handbook of clinical neurology 2016; (136()):1261-73.

    PMID: 27430467
  8. 8

    Fully Automated Deep Learning-Based Pipeline for Evans Index Measurement from Raw 3D MRI.

    Barough SS, Bilgel M, Moghekar A, et al.

    medRxiv : the preprint server for health sciences 2025; doi:10.64898/2025.11.30.25341302.

    PMID: 41409679
  9. 9

    Congenital Aqueductal Stenosis: Findings at Fetal MRI That Accurately Predict a Postnatal Diagnosis.

    Heaphy-Henault KJ, Guimaraes CV, Mehollin-Ray AR, et al.

    AJNR. American journal of neuroradiology 2018; (39(5)):942-948 doi:10.3174/ajnr.A5590.

    PMID: 29519789
  10. 10

    Unreliable sagittal T2-weighted flow void MRI in diagnosing third ventriculostomy: a case of long-standing obstructive hydrocephalus. Illustrative case.

    Neri N, Vignaroli A, Palandri G, Yamada S

    Journal of neurosurgery. Case lessons 2025; (10(3)).

    PMID: 40690802
  11. 11

    Evaluation of magnetic resonance imaging features of spontaneous third ventriculostomy in triventricular hydrocephalus.

    Arslan S, Karaman AK, Korkmazer B, et al.

    Acta radiologica (Stockholm, Sweden : 1987) 2025; (66(7)):740-747 doi:10.1177/02841851251324925.

    PMID: 40095621
  12. 12

    Anatomical subgroup analysis of the MERIDIAN cohort: ventriculomegaly.

    Griffiths PD, Brackley K, Bradburn M, et al.

    Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology 2017; (50(6)):736-744 doi:10.1002/uog.17475.

    PMID: 28337830
  13. 13

    Transcranial ultrasonography as a reliable instrument for the measurement of the cerebral ventricles in rats with experimental hydrocephalus: a pilot study.

    de Moura Silva GAP, da Silva SC, da Silva Beggiora P, et al.

    Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2021; (37(6)):1863-1869 doi:10.1007/s00381-021-05070-6.

    PMID: 33635419
  14. 14

    Neuroendoscopic Diagnosis and Treatment of Adolescent-Onset Aqueductal Stenosis: A Report of Two Cases Demonstrating the Utility of Endoscopic Third Ventriculostomy.

    Sakakibara Y, Yamamoto M, Watanabe T, et al.

    Cureus 2025; (17(11)):e96666 doi:10.7759/cureus.96666.

    PMID: 41404208

This guide to aqueductal stenosis imaging and radiology terms is for educational purposes only. Always consult your neurologist or neurosurgeon to interpret your specific MRI results and medical scans.

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