Phakomatoses Flashcards
Phakomatoses are characterized by:
- Hamartomas and Congenital Malformations affecting structures of ectodermal origin (visceral organs to a lesser extent)
- Ectodermal Origin:
- Nervous system
- Skin
- Globe
- Retina
- Ectodermal Origin:
What are 6 Inherited Cancer Predisposition Syndromes in which exposure to ionizing radiation should be minimized?
- Ataxia-telangiectasia
- Hereditary retinoblastoma
- Li Fraumeni syndrome
- Neurofibromatosis type 1
- Nevoid basal cell nevus syndrome
- Nijmegen breakage syndrome
NF1 gene is what?
Tumor supressor gene expressed in neurons, schwann cells, oligodendrocytes
Of patients with NF1 - will most develop OPGs?
No, only 15%
Of patients with OPGs, do most have NF1?
No, 40%
Is unilateral or bilateral involvement of an OPG classic for NF1?
Bilateral
What does FASI stand for? How is it defined?
- Focal Area of Signal Intensity - caused by Myelin Vacuolization (layers of myelin become separated as they spiral around the axon)
- No mass effect,
- No contrast enhancement
- No hemorrhage
- Increased diffusivity on DWI
What is this? Where are they usually found?
- FASI (in NF1) - Focal Area of Signal Intensity
- Found in globus pallidus, Internal Capsule, Corona radiata, Thalami, Deep cerebellar nuclei.
- NOT found in subcortical white matter/centrum semiovale
True or false: OGPs in NF1 are more likely to include primary involvement of the optic nerve (vs only the chiasm and optic radiations)
True - sporadic cases of OPG are more likely to involve only the chiasm/radiations and have a worse prognosis vs. indolent course of NF1 OPGs involving only optic nerve
Which course of OPG is more indolent: NF1 or sporadic?
NF1 (worse prognosis if sporadic)
What is the treatment for OPG in patients with NF1?
OPGs are low histological grade (pilocytic astrocytomas). They may even regress in patients with NF1. So - treatment should not be aggressive - wait to see if symptomatic/radiologic progression
How to differnetiate OPG from FASI?
OPGs have contiguity, mass effect, low T1 on post-contrast, enhancement after contrast, elevations in choline on MRS
What is an appropriate protocol for assessment of the Orbits in NF1?
Hi-res (<3mm) T1 and T2 FS axial/coronal sequences through globes, optic nerves, chiasm, followed by T1 FS - post Gad axial/coronal images. Followed by routine brain.
Where can an OPG extend when beyond the optic pathway?
- superiorly: into hypothalamus, fornices, septum pellucidum
- Laterally: Temporal lobes
- Posteriorly: Optic radiations
- Inferiorly: into crebral peduncles/brain stem.
Is this spectroscopy from a FASI or OPG?
OPG (increased choline to creatine ratio)
Gliomas in NF1 other than OPG: What can occur?
Basically - any other low or high grade neoplasm, but typically lower grade, ie pilocytic astrocytomas - which can occur almost anywhere - cerebral hemispheres - brainstem (midbrain and medulla are most common) - These tumors are more indolent than in the general population - can usually be watched. Sometimes no treatment until symptomatic progression.
What is this in a patient with NF1?
An area of FASI that turned into a pilocytic astrocytoma (this is why they need to be followed)
What is this in a patient with NF1?
- Pilocytic Astrocytoma (FASI would not enhance or have mass effect)
- Tumor course is more indolent than in general population - can usually be followed with no tx unless clinically symptomatic
- Image is of MRS of lesion - Cho/Cr is abnormally high (normal less than 1.5)
- Naa:Cr is abnormally low (normally greater than 2)
What is this in a patient with NF1?
Hypothalamic Hamartoma
- Should not be confused with a glioma
- Follows gray matter on all sequences; No enhancement
- With NF1, no association with gelastic seizures or precocious puberty (typically)
Why might a patient with NF1 develop hydrocephalus?
Usually from a tectal glioma causing mass effect on the aqueduct
What is the typical progression of FASIs?
Lesions appear during late infancy, with a peak of new lesions b/w 6-12 years old. Lesions then regress and are almost never seen after 20 years old.
Why do FASIs regress?
- Maybe due to remyelination or myelin repair.
Is there abnormal diffusivity in all of the white matter in NF1 - even if it looks normal?
Yes - abnormally increased, maybe related to abnormal myelination and subtle myelin vacuolization (one of the genes for correct myelination within the oligodendrocyte cell is embedded within the NF1 gene)
When should FASIs be followed if there is concern for tumor? And what would we be looking for?
6 months to a year - Enlargement, Mass effect, Enhancement, Reduced diffusion in solid portion, Increased blood volume, Increased Choline, Decreased Cr and NAA on MRS
In NF1, why are areas of FASI like Globus Pallidus and Thalamus sometimes also bright on T1
Thought to represent increased or remyelination (sort of repair after vacuolization) - typically occurs after T2 prolongation first appears and tends to persist after T2 prolongation disappears.
In NF1 - is increased T2 signal in the hippocampi worrisome?
No - This is not progressive. Hippocampal volume is normal or increased (as opposed to mesial temporal sclerosis) - is not progressive.
What does this person likely have?
NF1 - large CC due to increased myelination (maybe after repair?) or redundancy of fibers after decreased apoptosis?
