Identification of the Paraneurium With 7 T MRI in Normal Nerve Anatomy and Various Nerve Pathologies

The paraneurium is a distinct connective tissue sheath that loosely envelopes the epineurium. The space between the para- and epineurium (the subparaneurial compartment) holds significant clinical relevance, serving as a target for deposition of regional anesthesia and a potential pathway for the pathological spread of cysts and tumors. However, visualization of the paraneurial layer, as a separate structure from the epineurium, remains challenging with conventional MRI, especially in the absence of pathology. This study evaluated the visualization of the paraneurium using ultra-high-field 7-Tesla (7 T) MRI compared to conventional field strengths. We assessed normal nerve anatomy and a spectrum of pathological cases, including intraneural ganglion cysts, schwannomas, intraneural perineuriomas, and metastatic melanoma. The results demonstrated that 7 T MRI provides superior resolution and delineation of the paraneurium compared to 1.5 and 3 T systems. In normal anatomy, T1-weighted and proton density (PD) sequences provided optimal contrast between the paraneurium and surrounding adipose tissue. In contrast, for pathological cases, T2-weighted sequences with fat suppression were superior for depicting the paraneurium and identifying subparaneurial involvement. In conclusion, 7 T MRI offers a significant advantage in identifying the thin paraneurial layer. This capability provides valuable insights into the pathogenesis of tumor spread and holds promise for improving pre-operative planning and clinical decision-making in peripheral nerve pathology.