“Abnormalities” on structural images

Findings and clinical implicationsRobert D. Zimmerman MD FACR

Weill Cornell Medical College

DefinitionIncidental finding (IF)

“ A finding that has potential health or reproductive importance discovered in the course of conducting research but is beyond the aims of the study”

• Wolf et al. Managing incidental findings in human subjects research: analysis and recommendations. J Law Med Ethics 2008: 36 219

Ifs encountered depend on

• Age of subject population– Affects types of findings & their prevalence

• Imaging protocols used– Study exam is not a clinical exam and therefore may not detect an

abnormality even if present– If only perform anatomic T1 weighted sequence will fail to detect

processes that primarily alter tissue content rather than tissue volume• Subclinical or asymptomatic processes

– Stable or slowly progressive processes• How we (I) define IF

– Some findings are normal variants or so unlikely to be clinically significant that are not worth mentioning

Population

• 422 studies reviewed since 2008• Subjects 5-20 years old• ~ Mean approximately 15• No clinical neurologic abnormalities

IFs20 subjects – 4.8%

• Aqueductal stenosis with “arrested” hydrocephalus - 1• Middle fossa arachnoid cyst – 6• Focal or diffuse enlargement of subarachnoid spaces and or

low brain volume – 3• Chiari I malformation – 4• Focal white matter abnormality - 1 • Cavum septum pellucidum – 3• Intraventricular cyst – 1• Suspected aneurysm - 1

Review of literature

• IF in 10-50% of subjects– Pediatric subjects (2 studies) ~ 425 combined

• Incidence - 21% • However > 50% had sinusitis• Included pineal cysts and prominent perivascular spaces (normal

variants)• Clinical f/u in 1/3• Similar findings as in our population

– Adult and pediatric subjects• 18% IF

– 2/3 sinus disease– Aneurysm, 3 brain tumors

IF classification• 1) Clinically significant

– Likely to need treatment• Surgery, medical management

• 2) Potentially clinically significant– Probably will not require clinical treatment but may need:

• Full diagnostic MR or other imaging test• Referral to a neurologist or neurosurgeon• Follow-up assessment to insure not a progressive process

• 3) Incidental finding not likely to require intervention– Does patient need to know?– Should there be follow-up imaging

Practical and ethical implications

• No consensus in US or Europe• Are researchers obligated to look for and report IF?

– Researchers ~75%– Subjects - > 95%

• What images should be reviewed by a neuroradiologist?– Reactive – Only ask for review when researcher sees something

troublesome– Proactive – Neuroradiologist reviews all images– Very proactive – Include diagnostic sequences (e.g. FLAIR) even not

required for study design

IFType 1

• Aqueductal stenosis with hydrocephalus – 1• Asymptomatic however likely to become

symptomatic over time• Surgery

– Third ventriculostomy

IF Type 3

• Middle fossa arachnoid cyst – 6• Cavum septum pellucidum – 3• Intraventricular cyst – 1• Asymptomatic• Lesions usually static• No intervention necessary

– Probably should inform family of presence of arachnoid cyst.

– Arachnoid cysts may rarely enlarge and become hemorrhagic with head trauma

Arachnoid cysts• Congenital lesions due to splitting of the inner and

outer layers of arachnoid• Cells lining cyst secrete CSF • Locations

– Middle cranial fossa – Cerebral convexity– Suprasellar cistern– Posterior fossa

• Small and medium size cysts asymptomatic• Large cysts may become symptomatic

– Treatment – Cyst fenestration

IFType 2

• Focal or diffuse enlargement of subarachnoid spaces and/or low brain volume -3

• Chiari I malformation – 4• Focal white matter lesion -1• If static and asymptomatic no intervention

needed• If progressive needs to be followed and/or

treated

White matter lesions“UBO’s” Ischemia Trauma

Demyelination???

Usually asymptomaticNon-progressive

Chiari malformation• Disclaimer – I hate Chiari Malformation• Rant #1• History

– 1891: Chiari (German not Italian) reported 4 types– 1894: Arnold describes a single individual with meningomyelocoele

and mentioned in passing that the hindbrain is abnormal– 1912 – Students of Arnold review the hindbrain anomalies in what is

now called Chiari II malformation and name them the “Arnold Chiari malformation”

– Now – Term “Arnold Chiari” often used to describe all of these malformations (Wikipedia)

• So Arnold gets credit because of 1 incompletely described case of Chiari II and for all of the other malformations that he did not describe

Chiari malformation • Rant 2• At least 2 separate anomalies and maybe as many as 4• Chiari I completely separate from II-IV• Chiari II – Spina bifida

– Suite of brain & spinal cord abnormalities discovered at birth and now often in utero

– Primary defect is failure to form cerebral ventricles at appropriate time leading to small posterior fossa

– Genetic and/or nutritional • Folic Acid deficiency

– Surgery to correct meningomyelocoele (in utero)– Shunt for hydrocephalus

• Chiari III and IV very rare– May be severe versions of Chiari II or separate diseases

• I have never seen a Chiari IV

Chiari I malformation

• Not a brain anomaly• Not one thing• Anomalies of the osseous cranio-vertebral junction and/or

posterior fossa• Cerebellar tonsils “trapped” in the upper cervical spinal canal

leading to compression of the brain stem and altered CSF flow– Secondary syringomyelia and/or hydrocephalus

• Any disorder that traps tonsils below foramen magnum will present with similar clinical manifestations

Clinical manifestations• Tussive and/or positional headache• Signs of brain stem dysfunction

– Vertigo– Nystagmus (abnormal eye movements)– Lower cranial nerve dysfunction

• Syringomyelia– Loss of sensation of pain and temperature – Vibration and position– Eventual weakness and muscle atrophy– Insidious onset

• Hydrocephalus• Treatment

– Surgical decompression of the skull base– Shunt syrinx cavity and hydrocephalus– Surgery halts progression but does not restore lost function

Imaging features

• Osseous abnormalities– Platybasia– Short clivus– Small volume posterior fossa– Assimilation of C1 into skull base

• Brain/CSF– Narrow craniovertebral junction CSF space– Tonsil and brain stem distorted and impacted into cervical spinal canal– Syringomyelia (cord cyst)– Hydrocephalus

• Tonsil more than 5 mm below foramen magnum– Symptomatic Chiari usually > 10 mm

Rant #3

• It is hard to reliably measure tonsilar position– Tonsils often off midline and asymmetric– Precise definition of inferior margin of foramen

magnum difficult to determine• Therefore very difficult to differentiate

between normal low lying tonsils (< 5 mm) and mild Chiari I when no other abnormalities

• Don’t want to miss an asymptomatic Chiari I since may slowly progress to irreversible neurologic dysfunction

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5-12-07

Neoplasms

• Brain neoplasms second most common tumors in children (after leukemia)

• Many highly malignant acutely symptomatic• Lower grade tumors

• Juvenile Pilocytic Astrocytoma• Low grade (but malignant) astrocytoma• Oligodendroglioma

• Pituitary adenomas

Incidental vascular abnormalities

• Aneurysm – Out pouching of cerebral artery usually near base of brain– Rupture leads to catastrophic intracranial hemorrhage– However

• Small unruptured aneurysms (< 5 mm) typically don’t bleed• Aneurysms rare in children and young adults

– Acquired not congenital lesions• If suspect aneurysm on research study MRA can confirm or

exclude diagnosis and provide treatment guidance

Arteriovenous malformation (AVM)• Congenital abnormal connection between arteries

and veins without intervening capillary bed• Creates high flow “short circuit”• Typically presents in young adults with intracerebral

hemorrhage or seizures• Discovered incidentally in many individuals

undergoing MR for other reasons (e.g headache)• Treatment

– Surgery with or without endovascular partial ablation if presents with hemorrhage

– May treat or follow with imaging if no hemorrhage