Evidence notes
Evidence
Checked November 3, 2026; accuracy-audit fixes added November 4, 2026. Mirrors the “Evidence” tab of the planning doc.
Opened means the source page itself was opened and read during the November 4 accuracy checks (CLAUDE.md rule 1a, check 1), not just a search summary. Quotes for opened sources are in the audit reports in docs/audits/.
Every medical sentence on the site and every shape in the 3D model is listed here with the source it rests on. Nothing medical ships without a row in this file. The exact site wording lives in docs/COPY.md.
| Verdict | Meaning |
|---|---|
| Verified | An authoritative source states it directly |
| Partly supported | True with a qualifier; the site wording carries that qualifier |
| Simplified | Accurate in substance but drawn or worded simply for patients; the simplification is named on the site |
| Removed | Not supported; taken off the site |
Preferred sources, in order: NIH/NINDS and NLM, peer-reviewed research, major medical centers, then patient organizations for their own details.
Medical claims
| # | Topic | Site wording (summary) | Verdict | Sources |
|---|---|---|---|---|
| 1 | What Chiari is | The lowest part of the cerebellum (the tonsils) extends below the foramen magnum. The cerebellum helps control balance and coordination. Often linked to a smaller or differently shaped lower back of the skull, which crowds the brain; less often it develops later in life | Verified | NINDS fact sheet PDF, StatPearls, Radiopaedia, Cleveland Clinic |
| 2 | Who has it | Most people are born with the skull differences that lead to it; some never have symptoms, others first notice them as teens or adults | Verified | NINDS, Mayo Clinic, Cleveland Clinic |
| 3 | How it’s found | Usually an MRI plus a doctor’s exam; sometimes by chance. “A doctor looks at the scan together with your symptoms” (changed Nov 4 from naming a neurologist or neurosurgeon, which no opened source says) | Verified | NINDS, Mayo Clinic, Cleveland Clinic (opened: “your healthcare provider will ask about your symptoms”), PMC12888059 (opened: “clinical decision-making must integrate both imaging and patient-reported symptoms”) |
| 4 | Classic headache | Back of the head, after coughing, sneezing or straining | Verified | NINDS, Mayo Clinic, StatPearls |
| 5 | Other symptoms | Neck pain; dizziness and balance trouble; numbness or tingling in hands and feet; weakness or trouble with fine hand movements; trouble swallowing or speaking (changed Nov 4 from “voice changes”: NINDS says “Trouble swallowing, breathing, or speaking”); breathing or sleep problems such as sleep apnea; ringing in the ears; blurry or double vision; a curve in the spine (scoliosis), especially in children. (Changed Nov 4: vision moved into the main list as “blurry or double”, since Cleveland Clinic lists “Double or blurred vision” with no “less often” group; scoliosis added: NINDS “A bend in the spine (scoliosis)”, MedlinePlus “Scoliosis (in children)”) | Verified | NINDS (opened), Cleveland Clinic (opened), NINDS: syringomyelia (opened: “Curvature of the spine (scoliosis); may be the only symptom in children”), PMC12888059 (opened: “In pediatric and adolescent patients, scoliosis may be a presenting feature”), MedlinePlus: syringomyelia (opened; this is the syringomyelia page, not a Chiari page), Mayo Clinic (care-network copy), Cleveland Clinic, StatPearls |
| 6 | No symptoms | Many people with Type I have no symptoms at all | Verified | NINDS, Mayo Clinic, StatPearls |
| 7 | The 5 mm measurement | About 5 mm is the traditional cutoff. How far the tonsils extend doesn’t always match how someone feels; some with clear descent have no symptoms and some under 5 mm do. Doctors also look at tonsil shape, fluid flow and whether a syrinx is present. (Changed Nov 4: “lower tonsils make symptoms somewhat more likely” removed; studies disagree, and the opened sources say only that descent “does not always correlate with symptom burden” and “is not sufficient to identify symptomatic patients”) | Verified | Review, PMC12888059 (opened), Polish J Radiol, PMC9834072 (opened), Massimi et al. 2022, Sekula et al. 2005, Radiopaedia, StatPearls |
| 8 | Brainstem | Connects the brain to the spinal cord; runs automatic functions such as breathing, heart rate and swallowing | Verified | Cleveland Clinic |
| 9 | Spinal fluid | Cushions the brain and spinal cord; with each heartbeat it pulses back and forth between the skull and the spinal canal | Verified (simplified) | Cleveland Clinic, Takizawa et al. 2017 (PMC5615451, opened: “a fast movement synchronized with the heartbeat”; breathing also moves it, so the card is simplified) |
| 10 | Fluid flow in Chiari | In many people, not all, flow is reduced or blocked at the foramen magnum; a cine MRI can show it | Verified | NINDS, surgical series, PMID 16823310 (81% abnormal flow), Radsource |
| 11 | Treatment | No symptoms: usually monitored. Symptoms: surgery often recommended; it improves or stabilizes symptoms in most people, damage already done may not fully reverse, some need more than one operation; a syrinx can be a reason for surgery even without symptoms | Verified | NINDS, StatPearls, Mayo Clinic, pediatric consensus |
| 12 | Awareness Month | September, widely recognized through state and city proclamations (not federal) | Verified | Michigan 2026, Virginia, Bobby Jones CSF |
| 13 | How common | Not on the site. If ever used: roughly 1% to 4% of people having brain MRIs, depending on age; not a general-population figure | Not used | Strahle et al. 2011, Meadows et al. 2000 |
| 14 | Cine MRI | A fluid-flow MRI (used in the visit-prep question) | Verified | Cleveland Clinic |
| 15 | How far the tonsils extend in Chiari I | “In one study of 160 people with Chiari I, the average was about 12 mm, but it ranged from 5 to 25 mm, and the number alone doesn’t decide who needs surgery.” (Replaces “in people who need surgery it’s often around 10 to 12 mm”, which had no row and implied the number decides surgery) | Verified | Polish J Radiol, PMC9834072 (opened): 160 patients, tonsillar herniation 12.4 ± 3.7 mm, range 5.0 to 25.4; “the presence of cerebellar tonsillar herniation is not sufficient to identify symptomatic patients or patients who require surgical treatment” |
Explorer structure cards
| Card | Site wording | Verdict | Sources (all opened Nov 4) |
|---|---|---|---|
| Cerebrum | The largest part of the brain, responsible for thinking, movement and the senses | Verified (simplified) | Cleveland Clinic: cerebrum: “the largest part of your brain and handles conscious thoughts and actions”; “muscle movements, language, processing what your senses pick up” |
| Corpus callosum | A thick band of nerve fibers connecting the left and right halves of the brain | Verified | Cleveland Clinic: corpus callosum: “a bundle of nerve fibers that allow your brain’s left and right hemispheres to communicate” |
| Cerebellum | The back part of the brain that helps control balance and coordination | Verified | Row 1; Cleveland Clinic: cerebellum |
| Fourth ventricle | A small fluid-filled space between the brainstem and cerebellum, where spinal fluid passes through | Verified | Cleveland Clinic: hydromyelia: “This hollow space is in the lower part of your brain, near your brainstem. It’s filled with cerebrospinal fluid”; PMC10485575: floor formed by the brainstem, roof partly by the cerebellum, fluid leaves through the median aperture “into the cisterna magna” |
| Brainstem | Row 8 | Verified | Row 8 |
| Foramen magnum | The opening at the base of the skull where the brainstem becomes the spinal cord | Verified | Cleveland Clinic: medulla oblongata: “connecting to your spinal cord through the foramen magnum, an opening at the bottom of your skull” |
| Spinal cord | Carries signals between the brain and the rest of the body | Verified | Cleveland Clinic: spinal cord: “carries nerve signals from your brain to the rest of your body and back” |
| C2 vertebra | The second bone of the neck. Its upward peg, the dens, sits just in front of the spinal cord | Verified | Cleveland Clinic: cervical spine: “Your second vertebra (C2), also called the axis”; PMC7549867: the odontoid process is “a superior projection of the axial vertebral body”, and the transverse ligament “bounds and constrains the dens posteriorly and prevents it from folding into the brainstem” |
| Syrinx (part 11) | Uses the approved syrinx definition (Syrinx table) | Verified | NINDS, Merck |
| Bone removed (part 11) | Uses the approved After decompression wording | Verified | After decompression table |
Avoid: the “300,000 Americans” figure in some proclamations; it isn’t from peer-reviewed research.
3D model shapes
McRae line: from the front edge of the foramen magnum (basion) to the back edge (opisthion). Tonsillar descent is the perpendicular distance from that line to the lowest tonsil tip, measured on the midline MRI image or the adjacent one where the tonsils sit lowest (Barkovich 1986, Radiopaedia).
| Feature | Typical | Chiari I | Sources |
|---|---|---|---|
| Tonsil tip | About 1 mm above the line (meta-analysis mean +1.13 mm; reference interval about 7 mm above to 5 mm below, from +6.93 to −4.67 mm; Barkovich 1986 found 8 mm above to 5 mm below in 200 people; lower in children, rises with age) | At least about 5 mm below by definition; model uses about 12 mm, the average in a study of 160 people with Chiari I (12.4 ± 3.7 mm, range 5.0 to 25.4; PMC9834072, opened); often reaches the C1 back arch | Meta-analysis, PubMed 41081848 (abstract seen in search only; the “3,940 people” count is not confirmed), Barkovich 1986 (PubMed 3096099, abstract via search), Polish J Radiol, SNI review |
| Tonsil shape | Rounded | Often pointed or peg-shaped | PMC11371388 (opened: “Cerebellar peg-like rather than rounded tonsils … are more common in patients with TH > 5 mm”), Radsource, Radiopaedia: peg-like tonsil |
| Fluid space behind the cerebellum (cisterna magna) | Open | Often crowded or narrowed | Milhorat 1999, Radsource |
| Posterior fossa | Normal | Smaller and crowded; brain size normal. The Simple model shows the same skull in both (see the clivus row) | Milhorat 1999 |
| Clivus | About 39 to 47 mm, depending on the study (controls 38.99 ± 2.67 mm in PMC9834072, opened). Simple model: 43.7 mm. Since 2026-11-04 its skull, skull base, brain and head above the foramen magnum are traced from the Z-Anatomy atlas (real proportions; Matthew’s decision), checked by npm run model:check |
Several millimeters shorter (2 to 9 mm across studies; 32.63 ± 3.97 mm in PMC9834072). Not shown in either model (Matthew, 2026-11-04): both keep one skull for all four views so the change you see is the tonsils | Polish J Radiol, Can J Neurol Sci, Acta Neurochir |
| Tentorium | Normal angle | Steeper. Not shown in the Simple model. Note: Sekula 2005 studied people with little or no tonsillar descent, so this needs a Chiari I source before the realistic model shows it | Sekula et al. 2005 |
| Brainstem, fourth ventricle | Normal | Normal position (fourth ventricle may be elongated). A low brainstem is a different category, “Chiari 1.5,” not shown | Radsource, Radiologica, Radiopaedia: Chiari 1.5 |
| Foramen magnum, front to back | About 33 to 36 mm (Simple model 35.3 mm). Realistic model: 38.4 mm, as in the Z-Anatomy atlas; within normal variation (36.2 ± 3.3 mm in controls, PMC9834072, opened), so left as is | Same | Polish J Radiol, JNRP morphometry |
| Spinal cord, upper neck | About 9 mm front to back (8.8 mm at C2, 8.7 mm at C4, 7.4 mm at C7). The MRI first look measured about 8 to 9 mm on the MNI152 template | Same | PMC8334714 (opened): “from 8.8 mm x 12.4 mm at C2 to 8.7 mm x 14 mm at C4 to 7.4 mm x 11.4 mm at C7”; docs/audits/2026-11-04-mri-first-look.md |
| Spinal canal, neck (front to back, bone to bone) | About 13 to 15 mm below C2 (normal range in a study of 295 adults); roomier at C1 and the foramen magnum. Closed at the back by the laminae. Simple model: 14.5 mm (checked by npm run model:check); vertebral bodies about 15 mm tall, discs about 4.5 mm |
Same | PMC2899662 (opened): “subjects with a normal canal, diameter of 13–15 mm” (C3 to C7) |
| Fluid pathway | Continuous: from the fourth ventricle outlet into the cisterna magna, around the tonsils, through the foramen magnum and down behind the cord | Tonsils plug the pathway at the foramen magnum | PMC10485575 (opened), Milhorat 1999 (“obliteration of the retrocerebellar cerebrospinal fluid spaces”, abstract) |
| Dens of C2 | Upright, tip below the basion, in front of the cord | Same in the basic view; tilted dens and basilar invagination are related variants, not shown | Polish J Radiol, Milhorat 1999 |
Midline simplification (Simplified): the tonsils sit just to either side of the midline and often descend unevenly. The model shows them at their lowest point on the midline view, as MRI measures them. The figure caption, the printed visit-prep sheet and the tonsil info card say so (PMC11371388, opened: “In adult CM1 patients with syringomyelia, most (91%) tonsillar herniations were asymmetrical”; Tubbs, via springermedizin).
Mockup figure vs built model: the mockup figure is illustrative, not to scale. Since 2026-11-04 the Simple figure and model take the head, skull, skull base and brain above the foramen magnum from midline cross-sections of the Z-Anatomy atlas (model/simple/reference/), and apply the numbers above at and below the foramen magnum (McRae line, tonsils, cord, canal, vertebrae). The realistic model (Phase 2) uses Z-Anatomy throughout.
Syrinx
| Feature | What the model shows | Sources |
|---|---|---|
| How often | Shown only as “often.” Studies range from about 20% to 85% depending on who was studied | StatPearls, AJNR 2016, Strahle 2011 |
| Location | Most often in the neck part of the cord; one study found the top end most often around C6, though it can start as high as C1 | AJNR 2016, NINDS: syringomyelia, Radsource |
| Shape | Long, spindle-shaped or beaded cavity near the center of the cord; about 5 vertebrae long on average | AJNR 2016, Merck Manual |
| Definition | “A fluid-filled cavity inside the spinal cord. It often develops alongside Chiari.” | NINDS, Merck, Mayo Clinic |
After decompression
The McRae line is still drawn after surgery. It marks where the edges of the opening were before the bone was removed, which is how tonsil position is measured on follow-up scans.
| Feature | What the model shows | Sources |
|---|---|---|
| Skull bone removed | A piece a few centimeters across at the back of the foramen magnum, sized to each patient; the model uses about 30 × 25 mm (exact size not stated on the site). (Changed Nov 4 from “about 3×3 to 3×4 cm”, which the Hu 2023 citation could not be confirmed for) | PMC11912941 (opened): “a 2.5 × 3 cm bone window”; PMC10478704 (opened): “suboccipital craniectomy with 3 cm in diameter around the foramen magnum”; PMC4584091 (opened) |
| C1 | Back arch removed, the middle part, about 25 mm (in some techniques only partly). Site text says “often” (changed Nov 4 from “usually”; NINDS: “and sometimes the top of the spine”; PMC12888059: “A C1 laminectomy is commonly performed”) | PMC11912941 (opened): “Approximately 2.5 cm of the middle part of the posterior arch of the atlas was removed”; PMC10478704 (opened): “C1 posterior arch was removed”; PMC4584091 (opened), Balasa et al. 2022 |
| Dural patch | Often; some surgeons remove bone only | Balasa 2022, Khalsa 2017 |
| Fluid space | Re-formed behind the cerebellum and joined to the fluid behind the cord | PMC10549945 (opened): fluid space behind the cerebellum enlarged after surgery; Balasa 2022, Khalsa 2017 |
| Tonsils | Often rise only partly (about 2 mm on average in one study) and may stay below the line. (Changed Nov 4 from “about 4 mm”, which could not be found in the cited sources) | PMC10549945 (opened): “The cerebellar tonsillar position inferior to the McRae line decreased 2 mm 3–6 months after surgery … and 0.8 mm more in following years” |
| Syrinx after surgery | Smaller in most people, rarely gone; symptoms can improve even when it doesn’t shrink | StatPearls, NINDS |
| Outcomes | “Results vary, and surgery isn’t right for everyone.” Reported improvement ranges widely across studies | MedlinePlus: syringomyelia (the syringomyelia page), StatPearls, NINDS, Park-Reeves consortium |
Organizations (Support page)
| Organization | Site wording | Donate link |
|---|---|---|
| Bobby Jones Chiari & Syringomyelia Foundation | Maintains an international patient registry (new enrollment currently paused), hosts a yearly research colloquium, and funds Chiari research grants and fellowships | bobbyjonescsf.org/donate-online |
| Conquer Chiari | Funds Chiari research, publishes patient education materials, and supported the Chiari1000 patient registry (now closed) | conquerchiari.org/donate |
| ASAP: American Syringomyelia & Chiari Alliance Project | Supports patients and families, publishes a newsletter, and has helped fund research into the genetics of Chiari | asap.org/donate |
The Washington University study “Redefining Chiari Malformations Type I” is NIH-funded and enrolling (study page).
Research studies summaries
Plain summaries of individual studies are kept in src/data/study-summaries.json. Each entry records:
- the date Matthew approved it;
- the listing’s last-update date it was checked against;
- its audit report.
Each summary is written from the full ClinicalTrials.gov listing (saved copies are in docs/audits/sources/) and checked by a fresh agent before approval. A summary only describes the study; it makes no claim about Chiari itself. When a listing changes after its check, the daily refresh’s issue lists the study again. (Rule added Nov 5, 2026.)
| Study | Listing checked | Audit | Approved |
|---|---|---|---|
| NCT06502431 | Last updated 2026-09-08 (opened 2026-11-05) | docs/audits/2026-11-05-study-summaries-audit.md |
2026-11-05 |
| NCT06724029 | Last updated 2026-03-30 (opened 2026-11-05) | docs/audits/2026-11-05-study-summaries-audit.md |
2026-11-05 |
Non-medical claims
| Claim | Verdict | Sources |
|---|---|---|
Browsers don’t send the part of a link after # to the server |
Verified (scripts on the page can still read it, so analytics must be configured not to record it) | RFC 3986 §3.5 |
| Cloudflare Web Analytics uses no cookies and doesn’t build a profile; collects page, referrer, country, browser and device, page-load timing | Verified; re-check cookies in the browser before launch | Cloudflare FAQ, Cloudflare blog |
| ClinicalTrials.gov is the U.S. government’s registry, run by the National Library of Medicine | Verified; terms ask for source credit, processed date and a note that summaries are changed | Terms |
| Z-Anatomy is CC BY-SA 4.0; BodyParts3D is CC BY-SA 2.1 Japan | Verified | Z-Anatomy, BodyParts3D license |
| WCAG 2.2 AA is the current W3C standard; U.S. ADA Title II rules cite WCAG 2.1 AA | Verified | Section508.gov |
Review history
- First research pass: four parallel research tracks (basics and symptoms, imaging and anatomy, syrinx and surgery, organizations). 14 corrections.
- Independent fact check: 16 final statements re-checked from scratch. 9 passed, 7 tightened, none wrong.
- Second pass, four fresh reviewers: about 115 English sentences on all screens (6 tightened); the anatomy figure (8 drawing fixes, re-rendered and checked); the Spanish page (16 fixes, missing sections added); non-medical claims (9 fixes, including the BodyParts3D credit and accessibility wording).
Still open (only people can close these)
- Done:
A person with medical training looks at each finished 3D view once.Matthew decided on 2026-11-04 not to use a medical reviewer. Replaced by the accuracy checks in CLAUDE.md rule 1a; reports indocs/audits/. - Done:
Open the blocked medical sources directly.Done Nov 4 for NINDS, Cleveland Clinic, MedlinePlus and PubMed Central (rows marked “opened”). - Still open: Still not openable from this environment: StatPearls (bot check), Mayo Clinic and Radiopaedia (refuse automated readers), PubMed abstracts, Frontiers, AJNR, QxMD, Manipal. Nothing on the site now rests on these alone; rows citing them also cite an opened source or are marked.
- Still open: A medical translator signs off on the Spanish.
- Still open: Confirm the Bobby Jones CSF registry status with them (their page says paused, last updated 2024).
- Still open: Before Explain It launches: confirm in the browser network tab that analytics requests don’t contain the note.
- Still open: “Symptoms can come and go and are often invisible” (Home and Explain It) has no source row yet. Open the NINDS fact sheet or StatPearls NBK431076 and add one (found Nov 5; see
docs/drafts/2026-11-05-explain-it-drafts.md). - Still open: Open mayoclinic.org by hand once to confirm the care-network copy matches.
Sources not opened
The NINDS Chiari imaging standards file (Word format) and two PubMed Central articles could not be opened. Nothing on the site rests on them alone.