#mrirad

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This week we are discussing imaging of brain tumors in adults. MRI with and without contrast is the imaging modality of choice for brain tumors, although many tumors are initially discovered at CT performed for other purposes.

Today’s case is a 75-year-old woman who presented with right-sided weakness. CT revealed a large, heterogeneous mass centered in the left thalamus / basal ganglia. Internal hypoattenuation is compatible with necrosis, while surrounding hypoattenuation is compatible with edema. There is obstructive hydrocephalus. MRI confirmed the findings and revealed peripheral, nodular enhancement and extension across the midline and along the brain stem.

Findings are highly suggestive of high-grade glioma. Stereotactic biopsy confirmed glioblastoma, IDH wild type.

Case courtesy of Bruno Di Muzio, Radiopaedia.org, rID: 40573

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Another clue to the differential diagnosis of brain tumors is whether the lesion crosses the midline. Today's image depicts several entities that commonly cross midline: lymphoma, glioblastoma (GMB), meningioma, and radiation necrosis (tumor mimic). Metastases should also be considered (as always for any intracranial lesion in an adult).

Other tumor mimics that can cross midline are infection, hemorrhage, and demyelinating disease (e.g. MS, NMO, or ADEM).

Image credit: radiologyassistant.nl

[teachingrounds]

Determining whether a tumor is Intra-axial (arising from the brain) versus extra-axial (arising from meninges, pituitary, etc.) is important to developing a differential diagnosis.

Today’s case is a supratentorial mass. Gray matter is seen along the medial edge of the tumor (red arrow) indicating this is intra-axial. The most common supratentorial intra-axial lesion in an adult is metastasis, followed by glioma. This was a melanoma metastasis.

Side note: Differential diagnosis for this lesion if it were extra-axial would be metastasis versus meningioma.

Image credit: RadiologyAssistatnt.nl

[teachingrounds]

Here's a nice case. Cine shows "septal bounce" during diastole. Post-contrast images revealed diffuse pericardial enhancement (image in comments).

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Findings are compatible with constrictive pericarditis. Case courtesy of Dr. Thomas Anderson.

[teachingrounds]

Q: What is the mechanism by which IV contrast agents create contrast?

A: It’s unique for each modality, as follows:

CT: Iodine atoms absorb x-rays, making tissues appear denser (brighter). MRI: Chelated gadolinium, with 8 unpaired electrons is highly paramagnetic, causing T1 shortening, leading to increased signal in T1-weighted images. Ultrasound: Microscopic bubbles scatter sound waves, making tissues appear hyperechoic.

[teachingrounds]

What imaging studies should be ordered with IV contrast?

For CT and MR, the well-known VINDICATE mnemonic can guide you: Studies to assess for Vascular, infectious, neoplastic, autoimmune, and endocrine/metabolic disorders are usually performed with contrast (except CT for pneumonia). Studies for degenerative and/or traumatic injuries are usually without contrast (except trauma “pan scans” or similar studies). Iatrogenic and congenital can go either way.

Contrast-enhance ultrasound can assess liver and kidney lesions but should be ordered in consultation with a radiologist.

When in doubt, consult the ACR appropriateness criteria or a local radiologist.

[teachingrounds]

American College of Radiology no longer recommends interruption of breastfeeding after IV contrast administration.

Less than 0.01% of intervascular dose of iodinated contrast and less than 0.0004% of Gd-based contrast is absorbed from the GI tract of the child, far less than the permissible dose of IV contrast in neonates. Theoretical risks to the child are direct toxicity and allergic sensitization or reaction, but these have not been reported.  

Read more about this and anything else you want to know about contrast in the ACR Contrast Manual, a regularly updated, evidence-based consensus statement. For the remainder of the week, we’ll summarize topics discussed in the Manual.

[teachingrounds]

After birth, a child with spina bifida diagnosed in utero can be imaged with MRI to evaluate for other abnormalities (tethered cord, split cord, filar/intradural lipoma, among others).

Case: Myelomeningocele with tethered cord. Sagittal and axial T2-weighted MRI of the lumbar spine of an 18 year-old male. Large hyperintense cystic structure is seen in the posterior  soft tissues, with communication to the spinal canal. The cord terminates at L3 (normal is L1-L2) and is abnormally apposed to the posterior dura. Sacral nerve roots and thecal sac herniate into the posterior myelomeningocele.

Case courtesy of Dr Hidayatullah Hamidi, Radiopaedia.org, rID: 70353

#TeachingRounds #FOAMed #FOAMRad #Neuroradiology #Neurology #Pediatrics #Peds #PedsRad #PediatricRadiology #PedsNeuro #MRI #MRIRad #Spine #spinabifida #congenital