History :
This 24 y/o gentleman had Generalized tight sensation in limbs days ago and had seizure since childhood.

Image finding :
MRI of brain without contrast shows :
-Expansile lesion at R't frontal diploic space with hypointensity on both T1WI & T2WI.
-The inner and outer tables are preserved.
-No abnormal SI change in the visible brain parenchyma.
-The intracranial vascularture seems intact on T2WI.

Diagnosis :
Fibrous dysplasia.

Discussion :
FIBROMUSCULAR DYSPLASIA
=nonatherosclerotic angiopathy of unknown pathogenesis
Incidence: <1% of cerebral angiographies
Age:2/3 >50 years; M:F = 1:9
Associated with: brain ischemia (up to 50%), intracranial aneurysms (up to 30%), intracranial tumors (30%), bruits, trauma
Location:
-cervical + intracranial ICA (85%),
-vertebral artery (7%);
-both anterior + posterior circulation (8%);
-bilateral (60-65%)
-simultaneous involvement of renal / muscular arteries in 3%
Angio: length of affected vessel from 0.5 cm to several cm
Types:

1. Medial fibroplasia = fibromuscular hyperplasia (80%) string of beads = alternating zones of widening + narrowing tubular narrowing
2. Intimal smooth concentric tubular narrowing (DDx: Takayasu arteritis, sclerosing arteritis, vessel spasm, arterial hypoplasia)
3. Subadventitial hyperplasia
4. Atypical fibromuscular dysplasia (= ? variant of intimal fibroplasia) web = smooth / corrugated mass involving only one wall of vessel + projecting into lumen (DDx: atherosclerotic disease, posttraumatic aneurysm)

Cx:
-dissection (in 3%), macroaneurysm

Prognosis:
-tends to remain stable / minimal progression
Rx:only when symptoms progress