A 45-year-old with NF1 presents for MRI brain. Multiple T2/FLAIR hyperintense foci are identified in the globus pallidus, thalamus, and cerebellar white matter that do not enhance and show no mass effect. These are called 'unidentified bright objects' (UBOs) or focal areas of signal intensity (FASIs). What is their histological substrate?

• A Low-grade astrocytomas (pilocytic)
• B Microhaemorrhages from small vessel disease
• C Areas of abnormal myelin vacuolisation and spongiosis (intramyelinic oedema) ✓
• D Active demyelinating plaques

Explanation

UBOs/FASIs in NF1 represent foci of abnormal myelin vacuolisation and intramyelinic oedema (spongiosis) — not true neoplasms or demyelination. Pathologically, they show vacuolated myelin sheaths with gliosis. They are characteristically non-enhancing, without mass effect, and tend to involute with age. They must be distinguished from optic pathway gliomas and other NF1-associated neoplasms, which show mass effect and variable enhancement.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.