Dear friends
I received several answers, pointing out that the dorsal configuration of a MN is due to the location distal to the intermetatarsal ligament, obviously also dependent on the position of the joint/toe, and prone/supine. Thank you all, it makes my life both easier and more difficult 😀
Here are some of the responses:
Q1: Is that possible? And what structures are we looking at dorsally?
Yes it is. Morton Neuroma can displace dorsally if the intermetatarsal ligament is torn, or depending on the position the foot was placed during the MR scanning process.
Q2: Would you prefer T1 or T2 or both to diagnose a Mortons neuroma, or both?
T1 is the one I trust more.
Thanks….of course I’ve seen this, and it is annoying….because it challenges our understanding of the anatomy.
I think the answer is that it is originating plantar to the DTIL, but extending beyond and cranial to the level of the ligament (which we don’t usually see well, but infer).
Of course, it is common to have adjacent IM bursal inflammation (the article mentions this, but fails to mention that it just as commonly accompanies pseudoneuroma….which is why it is a useless "correlated sign" for either).
In your example, it looks like it’s just neuroma.
Another caveat…not relevant here, is that the DTIL is often disrupted with neurectomy….so all bets are off anatomically after surgery.
I prefer T1 to look for neuroma….since it is so commonly isosignal to surrounding suppressed fat in PDFS or T2FS images….but the fluid sensitive images in the short axis are complementary….to see PP tear and bursitis—-I don’t think you can sacrifice either.
In the article you share there is a beautiful US image from Filip of plantar vein thrombosis….I have never recognized this at the level of the MT heads / MTP joints….can’t imagine how many I’ve missed. Have definitely seen it in the hind and midfoot…but now I’m nervous!
Morton’s neuroma arises from the common plantar digital nerves as we know, passing plantar to the intermetatarsal ligaments. So neuromas should by default be located on the plantar side of the intermetatarsal ligament. Dorsally in the intermetatarsal space is the intermetatarsal bursa. From what I’ve read, the shape and location of a Morton’s neuroma depends on the position. Morton’s neuroma appears different on MR imaging in prone, supine, or weight-bearing positions. Morton’s neuroma at both supine and weight-bearing positions shows slight distal migration along the axis of the metatarsal ray. On the images obtained perpendicular to the metatarsal bone with the patient in the weight-bearing position, Morton’s neuroma is inverted pear shaped and located above the plantar cortical line, that is, dorsally in the intermetatarsal space. So in my opinion this is a regular dorsal Morton’s neuroma.
I prefer T2 to diagnose Mortons neuroma. But using both T1 and T2 coronal images is a better way.
Q1- yes with surgical proof
Q2- T1>T2
Beyond the MTPJ and intermetatarsal ligament the nerve curves upward into the toe and lies anterior to the bursa.
On the long axis view it appears distal to the bursa. In the short axis view we have to scroll beyond the MTPJ to see the neuroma, so the classic diagrams are wrong.
That looks like a pretty standard position. I see a lot of these – when you trace the plantar digital nerve it arcs dorsally just distal to the DTML. The bursa is dorsoproximal.
And I also received this link, which has some interesting thoughts on the development of Mortons neuroma, also challenging the traditional diagrams:
https://pubmed.ncbi.nlm.nih.gov/17880876/
Thank you all, have a great weekend!
Best regards
Roar
Norway
Hi again
Sorry to bother you again with some trivial toe stuff…
After Hilary’s excellent plantar plate lecture at the ISS, I have tried to inspire my MSK radiologists to pay attention to the differentials of a Morton neuroma.
One case sent to me had a dorsal protrusion in the 3/4 space, and I said that this can not be a Mortons neuroma. My colleague then sent me this article, and pointed out that fig 13 shows a dorsal Mortons neuroma, as in the enclosed image.
Therefore:
Q1: Is that possible? And what structures are we looking at dorsally?
Q2: Would you prefer T1 or T2 or both to diagnose a Mortons neuroma, or both?
Sorry again to bother you all with small problems 🙂
Best regards
Roar Pedersen
Norway
