T2 Hypointense Extra-Axial Lesions

Bronwyn E. Hamilton, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

CT may help confirm suspected bony or calcified lesions
T2 hypointense lesions due to high cellularity & blood products often also restrict on DWI
Primary osseous lesions may mimic an extra-axial lesion (i.e., fibrous dysplasia, exostosis)

Helpful Clues for Common Diagnoses

MR Artifacts, Flow-Related
- Phase artifacts due to flowing blood or CSF
- Periodic (pulsation) artifacts usually extend outside skull
- Common sites of CSF flow artifacts: Foramen of Monro, cerebral aqueduct, 4th ventricle, prepontine cistern
MR Artifacts, Magnetic Susceptibility
- Susceptibility artifacts typically rounded/ovoid & markedly worse on GRE > DWI > fat saturated images
- Usually absent on spin echo sequences
- Common at air-bone interfaces, frontal & temporal bones
- Common surrounding aneurysm clips
Pneumocephalus
- Evidence of recent craniotomy or trauma
- Completely black signal
- Non-dependent location
Physiological Calcification, Dura
- Anterior parafalcine region most common
- Ossification may demonstrate T1 hyperintensity centrally due to fatty marrow (mimics blood or lipoma)
- Associations with chronic renal failure, where it may be more extensive
Meningioma
- Enhancing extra-axial mass with dural tail
- Often T2 hypointense from high cellularity or intrinsic calcification
Metastases, Skull and Meningeal
- Enhancing extra-axial mass
- Meningeal metastases typically associated with skull involvement
- T2 hypointense if associated blood products (melanoma, renal cell carcinoma)
- Primary tumor often known
Schwannoma
- Homogeneously enhancing extra-axial mass along cranial nerves, CPA most common
- May show T2 hypointensity
- T2 hyperintense cystic change is common

Helpful Clues for Less Common Diagnoses

Epidural Hematoma
- Epidural collection in a trauma patient
- Hyperacute, mixed & chronic hematomas may be T2 hypointense
- GRE may show susceptibility artifact
Subdural Hematoma, Mixed
- Subdural collection in a trauma patient
- Hyperacute, mixed age & chronic hematomas may be T2 hypointense
- GRE may show susceptibility artifact
Saccular Aneurysm
- Round/ovoid T2 hypointense mass
- Flow artifact in phase encoding direction
- When thrombosed, challenging diagnosis
  - Maintain high suspicion when anatomically near vascular structures!
Lymphoma, Metastatic, Intracranial
- Often a T2 hypointense dural lesion
- Hypointensity related to high nuclear to cytoplasmic ratio
- Systemic disease usually present
- Mimics other metastases

Helpful Clues for Rare Diagnoses

Neurosarcoid
- Hypointense dural lesion(s) ± leptomeningeal disease > > parenchymal disease
- Dural, leptomeningeal, subarachnoid space enhancement
- 5% present as solitary dural-based extra-axial mass
- Majority of patients have systemic disease
Dural A-V Fistula
- Network of tiny vessels in wall of thrombosed dural venous sinus
- Isointense thrombosed sinus ± “flow voids”
- Look for serpiginous foci in CSF
Leukemia
- Usually a dural-based enhancing mass
- Commonly hypointense
- Most often a complication of acute myelogenous leukemia
Hypertrophic Pachymeningitis
- Diffuse dural thickening without known etiology
- Involves at least 75% of dural surface
- Typically T2 hyperintense
- Dense fibrosing pseudotumor may appear “black” (rare)
- Diagnosis of exclusion
Extramedullary Hematopoiesis
- Juxta-osseous smooth homogeneous masses in chronic anemias or marrow depletion patients
- Typically T2 hyperintense; rarely T2 hypointense
Hemangiopericytoma
- Lobular, enhancing extra-axial mass with dural attachment, ± skull erosion
- May mimic meningioma, but without Ca++ or hyperostosis
- Typically heterogeneously T2 hypointense
Retained Pantopaque
- Signal parallels fat (shortens T1/T2)
- Usually older patients since not in use since late 1980s