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Type:
Educational Exhibit
Keywords:
Education and training, Diagnostic procedure, MR, Neuroradiology peripheral nerve, Musculoskeletal soft tissue, Extremities
Authors:
M. J. García Ortega, D. Dunlop, A. Benito Ysamat, I. D. Domínguez Paillacho, R. Montero Perez-Barquero; Córdoba/ES
DOI:
10.1594/ecr2017/C-1153
Background
Benign tumors of the peripheral nerve sheath can be classified into two main groups: Schwannomas (neurilemoma) and Neurofibromas.
Treatment of these tumors varies depending on the symptomatology. Schwannomas grow eccentrically from the nerve,
because they have a capsule that facilitates their surgical excision,
preserving the affected nerve.
In the other hand,
localized neurofibromas tends to grow intraneurally,
so complete excision is not possible and the nerve must removed as well.
Radiological differentiation between neurofibroma and schwannoma may help the surgeon to plan the intervention and warn of the possibility of loss of nerve function.
Is not only important the differentiation between schwannomas,
neurofibromas and it’s subtypes (localized,
diffuse and plexiform),
but also to differentiate them from other tumors of the nerve sheath,
such as Morton's neuroma,
traumatic neuroma,
sheath ganglion and nerve fibrolipoma.
It is also possible the malignization of peripheral nerves tumors,
what may change surgical approach,
being necessary a complete excision as possible.
Several imaging findings suggest the diagnosis of a nerve sheath tumor,
such as an spindle morphology,
certain intrinsic features of the tumor,
and their localization have been described.
The visualization of a fusiform mass that enters and exits a tubular structure,
in a typical localization of a nerve (fig.
1), and signal-intensity characteristics may help the diagnosis (table 1): the fascicular sign,
target sign,
fat shift sign,
contrast enhancement pattern,
and the presence of cystic or necrotic areas.
MRI findings
|
Neurofibroma
|
Schwannoma
|
Mass-nerve relationship
|
Central
|
Peripheral
|
Target sign
|
+++
|
+
|
Fascicular sign
|
+
|
++
|
Cystic or necrotic areas
|
-/+
|
++
|
Enhancement pattern
|
Central/diffuse
|
Peripheral/diffuse
|
Table 1.
MRI finding of Neurofibromas and Schwannomas
Other findings such as poorly defined margins,
rapid growth rate,
major vascularization,
and central necrosis are highly suggestive of malignancy.