Brain Mets
Parenchyma, leptomeninges, pachymeninges and skull.
General 1
10 Brain Mets : 1 Primary Brain Tumour.
30% of brain mets present as solitary lesion.
Incidence: 14 per 100K py (Sweden 2006). Increasing due to improved management of primary disease and more x-sectional on the dying. Note increased risk of brain mets relapse in Herceptin treated patients.
Prognosis: Very poor
Median survival in WBRT treated cohort from unsorted tumours = 3.4 months
OS = 6% at 2 yrs & 2% at 5 yrs
Table
| Primary | Freq | Site | Skull Mets | Pachymeningeal | Lepto / CSF | Radiology |
|---|---|---|---|---|---|---|
| Breast | 15% | Cerebellum / Post.Fossa | 50% of calvarial | 34% are Breast | ++ | |
| Lung | 17% | Parietal / Occipital | 13% are lung | ++ | ||
| Renal | 11% | |||||
| Melanoma | 8% | + | ||||
| Prostate | 40% of skull base | 17% are prostate | ||||
| Lymphoma | 8% of skull base | +++ | ||||
| H+N | 10% are H+N |
Renal incidence seems too high and breast / lung too low for Worthing.
Parenchymal Mets
Usually at grey-white matter interface or watersheds
-- 80% Cerebral hemispheres
-- 15% Cerebellum
-- 5% Basal Ganglia
Nearly 50% are solitary especially Renal / GI / Urogynae.
Multiple tend to be Breast / Lung / Melanoma
Haemorrhage:
- Melanoma (and melanin is paramagnetic)
- Thyroid
- Renal
Calcification:
- Lung
- Breast
- CRC
Vasogenic Oedema:
- Lung >>
- Breast >
- Oesophageal
Don't forget PCNSL
Pachymeningeal Mets
aka Dural mets.
Prognosis is good at 2x that of parenchymal & leptomeningeal mets
~ 34% invade underlying brain. ( ~50% of these have vasogenic oedema )
~ 44% of dural mets have 'dural tail' sign.
Most are frontal and parietal.
Leptomeningeal
MRI >> CT
FLAIR + T1 post Gd (volumes).
NB: Look at the CN for enhancement.
Site: (in frequency order)
- Cerebellum
- Occipital lobe
- VII / VIII CNs
- Lateral Ventricle ependymal surfaces.
Approach to Solitary lesion.
30% present as Solitary lesions.
- Mets vs Primary: Look at periphery as it is cells + oedema in a primary vs just oedema in a met. But there are no very clear answers from the use of advanced imaging.
- Met/Primary vs Abscess: ADC especially in centre is useful in cystic / ring enhancing lesions as low ADC is relatively maintained in abscesses. But GBM can be low ADC
- High Grade Glioma vs Met: is very difficult.
All advanced imaging has inconsistent findings in reviews of literature.
Post-Treatment Change.
Pseudo-progression is a thing post SRS (and other ones as well),
6 to 8 weeks Post-Treatment
Seen in UP TO 1/3
Better prognosis with 2 months increase in OS
Signs of Pseudo-progression, include:
- Increase size of lesion.
- Central decrease T2.
- Blurred peripheral enhancement.
- Increase perilesional oedema.
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Sahdev A and Vinnicombe S. Husband & Resnek Imaging in Oncology. CRC Press 2020. ↩