Schwann cells are not normally present in the cerebellar parenchyma and it is difficult to explain the origin of intracranial schwannomas. (Umredkar, 2011). Only 35 cases had been described up to 1998 (Zagardo, 1998), 44 cases up to 2004 (Collela, 2004) and only 70 cases up to 2011 (Umredkar, 2011). Many hypotheses such as the possible origin of Schwann cells in perivascular plexuses have been proposed to explain this type of lesions unrelated to cranial nerves. (Umredkar, 2011). More studies are required to define theories, allow clinical suspicion and be able to establish the best clinical and surgical management for these patients as well as their vital and functional prognosis.

Hi Andrea Ortiz Ordonez ,

Intra- and extra-cranial schwannomas are very rare as you have mentioned in the demographics.

In 1996, Sharma and colleagues demonstrated that: "the lesionis usually solitary and in only two cases, an associated neurofibromatosis (NF1 and NF2) was found."

https://jnnp.bmj.com/content/60/2/200.short

This was a quite fascinating result, and there have been some imaging studies recently that explained the structural and functional deficits of this disease in details:

Chapter Chapter 45. Intracranial Schwannomas

The following is also a good case report study showing that the majority of subtentorial schwannomas are located in the brainstem. But even clear conclusions cannot be achieved in each case before operations because of the rareness of the disease.

"Therefore, subtentorial schwannoma is typically diagnosed on the basis of postoperative pathological analysis. If the tumor can be completely removed, the prognosis of the patient is good."

Article Intracerebral schwannoma: A case report and literature review

Thanks Bahman Sadeghi, for your valuable response and references.

I have a case of infratentorial midline tumor who underwent gross total resection, however survival was only 6months. Histopathology showed malignant nerve sheath tumor with rhabdomyoblastic differentiation (Triton), I haven't found any previous case in such location. Understanding it's origen would certainly shed some light to treat this entity. Thanks again.

Thanks Andrea Ortiz Ordonez ,

As far as I know, MTT has a poorer prognosis than MPNSTs and can have much worse symptoms and less survival period, although diagnosis of both would be difficult. And that is unfortunately the case that most of the patients just have a few months of prolonged survival even with complete resection and radiotherapy, etc.

Agree. Understanding the relation of the region (which nerve or region) and then having a high throughput IHC testcould be definitely helpful in prognosis and course of treatment. This seems like "similar" to an RMS MTT-type in a cranial nerve.

First I thought that it is kind of associated with a cranial nerve (i.e. trochlear), but as I read your comments I saw that it is apparently just in the infratentorial midline region of the brain. More imaging data (DTI) could be very useful. I also searched a bit but just found the following about the lateral region:

Article Infratentorial lateral supracerebellar approach for trochlea...

Although you mentioned that your case study had no association with a cranial nerve, the following paper describes a case of MPNST in acoustic nerve in which the way they conducted the prognosis could be interesting. Apparently, it was also a RMS like MPNST. The authors have done a thorough IHC and seems that they got a good result in diagnosis of the disease: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1440-1827.1993.tb01132.x

Thanks again Bahman Sadegi, for sharing all this highlighted information. I found it very useful.

Hi Andrea Ortiz Ordonez ,

Great to see that you and your colleagues have published the paper related to this discussion and subject. Fascinating! Very interested to read the full-text if available in here.

Thanks Bahman! I just shared full article with you. I will be happy to hear your comments.