MRI/PET vs. CT/SPECT for diagnosing Schwannomae

[DarkProtoman]

Hi! I'm new here, I've been wondering:

Which is more precise for diagnosing Schwannomae, coregistered MRI/PET, or coregistered CT/SPECT? And why does a Schwannoma show up on an MRI w/ contrast, but not on a plain MRI? Is the contrast IV or IT?

Thank you, all you neuroradiologists out there!!!!

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[Docxter]

Schwannomas are often seen both on noncontrast and postcontrast images. The contrast uptake just makes them easier to seen by making them much more conspicuous. And also the ease or difficulty in seeing them depends on what location schwannoma you are talking about.

Why is your purpose of coregistering the MRI or CT with PET or SPECT?

 

[DarkProtoman]

Schwannomas are often seen both on noncontrast and postcontrast images. The contrast uptake just makes them easier to seen by making them much more conspicuous. And also the ease or difficulty in seeing them depends on what location schwannoma you are talking about.

Why is your purpose of coregistering the MRI or CT with PET or SPECT?

My purpose of coregistering the images is b/c tumors tend to have a higher metabolic activity then the surrounding non-neoplastic tissue, so they'd stand out. Would you use MR/PET, or CT/SPECT, for diagnosing of, say, lymphoma?

And I've seen cases where a plain MRI was *completely* normal, but an MRI w/ contrast showed a *massive* Schwannoma on the 9th, 10th, and 11th cranial nerves.

 

[Docxter]

My purpose of coregistering the images is b/c tumors tend to have a higher metabolic activity then the surrounding non-neoplastic tissue, so they'd stand out. Would you use MR/PET, or CT/SPECT, for diagnosing of, say, lymphoma?

Yes, I know what a PET scan is and what it does. And no, lymphoma is not a good comparison example to make your point. PET is very helpful in follow-up and management of lymphomas, but this utility has not been convincingly demonstrated in the FDG-PET variable benign schwannomas. Exception may potentially be the rare malignant schwannomas.

I don't know of any study that has compared the utility of MRI\PET vs. CT\SPECT in this setting, but my guess is that just the MRI portion will easily win over CT\SPECT.

And I've seen cases where a plain MRI was *completely* normal, but an MRI w/ contrast showed a *massive* Schwannoma on the 9th, 10th, and 11th cranial nerves.

A massive schwannoma not seen on noncontrast MR but seen only on postcontrast only? That's not possible. The only explanation must be the person looking at the precontrast scan just missed it.

 

[DarkProtoman]

Yes, I know what a PET scan is and what it does. And no, lymphoma is not a good comparison example to make your point. PET is very helpful in follow-up and management of lymphomas, but this utility has not been convincingly demonstrated in the FDG-PET variable benign schwannomas. Exception may potentially be the rare malignant schwannomas.

I don't know of any study that has compared the utility of MRI\PET vs. CT\SPECT in this setting, but my guess is that just the MRI portion will easily win over CT\SPECT.

Maybe you could do a study? Get some (more) publications under your belt. And are maliginant Schwannomae called Schwannosarcomae, or Schwannocarcinomae?

A massive schwannoma not seen on noncontrast MR but seen only on postcontrast only? That's not possible. The only explanation must be the person looking at the precontrast scan just missed it.

Well, the pre- and postcontrast MRIs *were* two years apart, so that definitely factored in I bet.

 

[f_w]

Occams razor, as applied to radiology:

Why do a $2500 MRI to diagnose a renal cyst if a $550 US will do ?

Why add a PET or SPECT to diagnose a putative Schwannoma if a contrast MRI will do ? (unless you can come up with a highly specific PET tracer for 'Antoni A' cells that doesn't require an 8hr study and anesthesia on intubation standby).

 

[DarkProtoman]

Occams razor, as applied to radiology:

Why do a $2500 MRI to diagnose a renal cyst if a $550 US will do ?

Why add a PET or SPECT to diagnose a putative Schwannoma if a contrast MRI will do ? (unless you can come up with a highly specific PET tracer for 'Antoni A' cells that doesn't require an 8hr study and anesthesia on intubation standby).

OK, we've established that an MR/PET or CT/SPECT is overkill for benign Schwannomae. But what about grade 1 optic nerve gliosarcomae? Or would a simple MRI w/ IT gadolinium contrast suffice?

 

[f_w]

I do not understand your question.

Typically, a physician has a clinical scenario, and then he is looking for a test to answer a clinical question. You on the other hand pose a histologic diagnosis and then try to go back from there to decide which test is 'better' to detect this (rare) entity.

 

[Docxter]

OK, we've established that an MR/PET or CT/SPECT is overkill for benign Schwannomae. But what about grade 1 optic nerve gliosarcomae? Or would a simple MRI w/ IT gadolinium contrast suffice?

I don't know what an optic nerve gliosarcoma is. Are you talking about the run-of-the-mill grade I optic nerve gliomas? I happen to work in a very unique practice situation in which we see an average of 1-2 optic nerve or chiasmatic gliomas every day (obviously most of them just follow-ups), because of the very large NF-1 population referral base at our place. MRI has so far met all the needs for the detection and follow-up of these patients. And our oncologists and neuro-oncologists are happy with what we have.

As f_w said, what are you actually looking for?

Maybe you could do a study? Get some (more) publications under your belt.

Thank you for your genuine concerns for my career.

 

[DarkProtoman]

I don't know what an optic nerve gliosarcoma is. Are you talking about the run-of-the-mill grade I optic nerve gliomas? I happen to work in a very unique practice situation in which we see an average of 1-2 optic nerve or chiasmatic gliomas every day (obviously most of them just follow-ups), because of the very large NF-1 population referral base at our place. MRI has so far met all the needs for the detection and follow-up of these patients. And our oncologists and neuro-oncologists are happy with what we have.

As f_w said, what are you actually looking for?



Thank you for your genuine concerns for my career.

Well, I meant a malignant optic nerve glioma --I've this [possibly incorrect] habit of replacing "-oma" w/ "-sarcoma" when I'm talking about the malignant version of a benign tumor--

And, I was discussing w/ my internist friend at church, Dr Mark Christopher Asbill about this very subject, b/c we were talking about brain tumors, neuroradiology, etc., and I told him about this case I saw on DHC's "Mystery Diagnosis" where a girl had incontinence, double vision, migraines, etc., so she had a plain MRI, which came back negative; every Dr thought she was making things up, etc....to make long story short, she ended up seeing a physiatrist when she broke her neck in a car accident, her symptoms ablated when she had the cervical collar on, but as soon as she removed it, all of her symptoms returned w/ avengence, so her new physiatrist did a contrast MRI, which revealed a Schwannoma pressing on the 9th, 10th, 11th, and --if I remember correctly--, 12th cranial nerves. Her physiatrist referred her to a neurosurgeon, who excised the Schwannoma, and now she's all better!

And you're very welcome for my concerns about your career!

 

[f_w]

Schwannomas can indeed be quite isointense on T1 and T2 weighted native sequences. That, and the difficulty to sort out small IAC masses without contrast is the reason why most places will do w+wo studies for anything posterior fossa (and anytime I deal with a cheapskate HMO that doesn't want to pay for it, I will give a report that forces the referrers hand to armwrestle the insurance into a post-contrast study. ok with me, that way I get paid twice for something they could have gotten for about 20% more).