Peripheral soft tissue nerve sheath tumors, refers to nerve sheath tumors that occur outside of the cranium and spinal canal. Both have different MRI manifestations depending on the site of occurrence. This article focuses on peripheral nerve sheath tumor. I. Site distribution: It is most common to occur in the limbs, followed by the neck and axilla, and it is not uncommon to occur in the pelvis, mostly in the presacral region. Rare sites include the lumbar back and psoas major muscle. Histopathological features: Histologically, two main structures were seen: Antoni A and Antoni B. Antoni A is a cell-rich area, composed of chromatin-rich spindle cells; Antoni B is a stromal area with few cells and much mucus, with acidophilic characteristics; Antoni A and B are the basic components of nerve sheath tumors, and the distribution and proportion of Antoni A and B in the tumor varied. Antoni A and B are the basic tissue components of nerve sheath tumors, and the distribution and proportion of Antoni A and B in the tumor varies, so that their histological sections are not identical, and the pathological diagnosis of those with atypical arrangement of Antoni A and B is also quite difficult. In addition to HE staining, immunohistochemistry is also commonly used in the characterization and differential diagnosis of tumors. Neurosphincter tumor expresses S-100 antigen, so it has a strong positive reaction to S-100 staining, and neurofibroma is negative due to the lack of expression of S-100 antigen, and S-100 staining can differentiate neurosphincter tumor from neurofibroma. MRI examination method: Conventional MRI scanning sequence can basically complete the localization and qualitative diagnosis of the tumor. For atypical cases and when more information is needed, other scanning methods should be used. Enhanced perfusion MRI (PWI), can understand the distribution and passage of contrast agent first pass process in the arteries and capillaries of the tumor, and its results are different from the general enhancement effect. Diffusion-weighted MRI (DWI), detects the diffusion-restricted effect of water molecules in the tumor body, the degree of diffusion restriction varies among different tumors, and DWI has a certain differential diagnostic role in tumors. MR Spectroscopy (MRS) can detect the metabolites and their concentration in the tumor, and then analyze the histochemical composition of the tumor, according to which, we can compare the histochemical differences between different regions of the tumor and observe the relationship between the biological behavior of the tumor and the changes of metabolites in the tumor. Dynamic enhanced MRA (DCEMRA) can intuitively reflect the staining and blood supply characteristics of tumors in arterial phase, venous phase and later phases, and the DCEMRA performance of tumors with different histological types also have their own characteristics, which is of high value for judging the biological behaviors of soft tissue tumors. Fourth, MRI sign features and its pathologic basis: 1, rim sign. Neurosphincter tumors show isomuscular signals on T1WI, and show signal differences within the tumor on T2WI, with the Antoni A area showing isomuscular signals or slightly high signals, and the Antoni B area showing high signals, which are comparable to fat signals. In typical MRI, Antoni A is located in the central region of the tumor, and Antoni B shows a complete ring around Antoni A at the edge of the tumor, which varies in thickness and may be thin and linear at some levels. This sign is known as the rim sign. On fat suppression T2WI (FST2WI), the rim sign is significantly more common than on conventional T2WI, so FST2WI is necessary. This presentation, which is also called the target sign, is generally characterized by a relatively regular ring structure on the target sign, whereas the rim sign is relatively irregular, with a continuous and uneven thickness. Therefore, it is more accurate to use the rim sign than the target sign. 2.Differential enhancement. Scanning within 10 min after contrast injection showed significant enhancement of the Antoni A area, while the Antoni B area did not enhance or had no significant enhancement. The reported studies have not paid attention to the different effects of the enhancement of Antoni A and Antoni B, which were generally considered to be the significant enhancement of the tumor body after enhancement, and the enhancement effects of Antoni A and Antoni B were determined by their tissue structure. Antoni A is rich in cells and blood supply, and its strengthening is early and significant, while Antoni B is dominated by mucus matrix, and its strengthening is relatively weak and slow. Based on the presence of vascular components in both Antoni A and Antoni B, we questioned whether Antoni B would show delayed enhancement. Dynamic MRI at 60 min after contrast injection revealed that the enhancement of Antoni A had basically subsided by 40 min, while Antoni B showed significant enhancement at that time, and the enhancement effects of Antoni A and Antoni B were reversed compared with those at the beginning of the enhancement period. This shows that the enhancement of Antoni B is the result of the diffusion and aggregation of contrast agent in the mucus matrix. 3. PWI and DWI: On PWI, the nerve sheath tumor showed low perfusion changes, and the perfusion curve of Antoni B showed relatively high perfusion; on DWI, it showed moderate diffusion limitation, which was close to that of cavernous hemangioma; there was no diffusion limitation in Antoni B, and only a certain degree of limitation in Antoni A. The diffusion of Antoni B was not limited, and only a certain degree of limitation was observed in Antoni A. The diffusion of Antoni B was not limited. 4, MRS: MRS can only be collected on larger tumors, and metabolites such as Lip, Cho, and NAA can be detected on MRS maps of nerve sheath tumors. the differences in metabolites in Antoni A and B need to be studied with more samples. 5, DCEMRA: Nerve sheath tumors have no tumor staining on the arterial and venous phases of DCEMRA, and no blood-supplying arteries are shown. Neurofibromas, which show staining and blood supply arteries in their arterial phase, are distinctly different from nerve sheath tumors.DCEMRA manifestations and PWI manifestations are based on a common histologic basis. 6.Flower spot sign: when Antoni A area and Antoni B area are arranged irregularly, the signal strength of the tumor body is uneven on T2WI and enhancement image, which is like a flower spot, and it is difficult to diagnose by MRI at this time, but after grasping the histopathology of the tumor and the characteristics of the performance of MRI, a correct diagnosis can still be made.