Neurofibroma is a rare benign nerve sheath tumor composed of Schwann cells, perineural like cells and fibroblasts(10). It can be found in any peripheral nerve that can be invaded by neurofibroma, especially in lower limbs and upper limbs(2). There are generally three types: solitary, diffuse and plexiform. Among them, the solitary neurofibroma is usually a small polypoid mass with its maximum size of less than 2 cm(4, 11). Most neurofibromas appear as single lesions in dermis or subcutaneous, but there are still 10% cases related to NF-1, which is an autosomal dominant genetic disease, formerly known as Von Recklinghausen disease, with clinical features of cafe-au-lait pigmentation, benign skin and subcutaneous tumor known as neurofibroma, characteristic osteopathy, iris focal malformation(12, 13). In this case, we did not find a correlation performance. However, due to the effect of NF-1, this type of neurofibroma has larger volume, higher tendency of malignant transformation and higher recurrence rate (4, 8, 14). Therefore, when we encounter neurofibroma, we still need to actively look for other manifestations of Von Recklinghausen's disease to exclude the possibility of malignancy.
As the growth of neurofibroma is slow, and can occur at any age, has no sexual preference, and usually has no pain, numbness or other discomfort symptoms(15), its diagnosis is mainly depending on the result of imaging and microscopy. The differential diagnosis includes nodular fasciitis, myxoma, neurofibrosarcoma and adult rhabdomyoma, especially schwannoma(16, 17). Both schwannoma and neurofibroma belong to the peripheral nerve sheath tumor(7). They not only have homologous lesions, but also have similar imaging manifestations. Ultrasound can't distinguish them reliably, for their sonographic features are medium echo solid extension mass, generally without blood flow signal, which are the common features of soft tissue tumors(2). In the X-ray manifestations, since its soft tissue contrast is worse than that of MRI, and the bone is clearly displayed, X-ray is often used to judge the bone invasion or destruction of peripheral nerve tumors (30% − 50% of patients can see), such as aggressive damage, bone compression and displacement, external cystic change of bone, subperiosteal cyst and pseudarthrosis of tibia, etc.(18), which is also presented in our case, specifically the osteolytic manifestations of the ischial and pubic branches. But these imaging feature contribute a little to the differential diagnosis. Unfortunately, the MRI, which is the most sensitive imaging method for soft tissue, manifests neurofibroma may similar to those of schwannoma. They usually show low or equal signal compared with muscle on T1-weighted image(T1WI), high signal on T2-weighted image(T2WI), and can change with the enhancement of contrast agent, especially when the tumor has mucoid mechanism, it can show no or slight enhancement(8, 15). It is worth noting that compared with schwannoma, neurofibroma often lacks complete capsule, which may help us to distinguish common cases by MRI images(6). At the same time, when the myxoid tissue in the neurofibroma is rich enough, it can show a characteristic image from the schwannoma, which presents the low T2 signal central area of collagen tissue as the bull's eye, and the high T2 signal of the myxoid tissue as peripheral area(8). However, this case is extremely rare. The solitary mass is not only huge in size, particular in tumor site, but also has a complete capsule on MRI without the target sign, which leads to our erroneous initial diagnosis of schwannoma.
The final diagnosis depends on the pathological examination of the tumor, which is done by detecting the nerve cells contained in the tumor, as shown in this case. First, unlike schwannomas, the parent nerve of neurofibromas is usually separable in plexiforms rather than isolated ones(6). Secondly, neurofibroma is rich in mucoid tissue (Antoni B area), while schwannoma has a compact stroma (Antoni A area)(8). In addition, although both of them are composed of fusiform nerve sheath cells, the nuclei of neurofibroma are slender and wavy, while the nuclei of schwannoma are oblong and arranged closely and parallel to each other in palisade or incomplete voracies (Verocay bodies)(4, 15). Immunohistochemical results also provide the basis for differentiation, which is reflected in the uneven staining of S-100 protein, only local immune response to epithelial membrane antigen (EMA), and strong CD34 positive in neurofibroma, while schwannoma cells showed more intense and uniform staining of S-100 protein, and the capsule stained EMA(2, 4).
When clinical diagnosis of neurogenic tumor is made, we should routinely and safely performed biopsy using ultrasound or CT guidance to achieve pathological diagnosis, along with the tissue diagnosis recommended for surgical planning. But biopsy has a risk of causing nerve damage, which is likely to occur in this case as intraoperatively, we found that some of the nerve fiber tracts were extruded particularly thinly by the tumor. At present, the first choice of clinical treatment for neurofibromas is still complete resection, especially when symptoms occur or appearance are affected, the postoperative prognosis is good and the recurrence rate is low(2, 10). However, the parent nerve of neurofibromas is usually unseparable in solitary neurofibromas(6). Thus, it should be noted that under the premise of complete resection, the scope of tumor resection should be precisely determined, and microsurgery is recommended, at the same time, the parent nerve and non-involved nerve fibers need to be preserved as much as possible, so as to avoid serious risk of nerve injury and the sacrifice of the parent nerve. These require microsurgical skills and rich surgical experience of the chief surgeon. Alternative therapies include enucleation and subtotal resection, which are often used in the patients that completely resection may cause severe functional defects or cosmetic deformities. However, due to the inevitable recurrence caused by the residual tumor tissue, they are often not considered(6). Radiotherapy is also a feasible method, but it is only suitable for isolated lesions to control or reduce the growth of lesions, and it is effective for the treatment of juvenile angiofibroma(19). Recently, there is also a literature showing that photodynamic therapy is effective for solitary neurofibroma, but its long-term survival rate and long-term prognosis still need to be investigated(10).
In consideration of the limitation and huge type of the focus in this case, as well as the adverse effects on daily life, such as sitting and standing posture change obstacles and pain, we performed a complete resection of the tumor in this patient. After incision of the outer membrane, we peeled off the tumor, kept the normal nerve fiber bundle as much as possible, protected the large blood vessels, and covered the nerve blood vessel bundle with the re-suture of the muscle after resection. There was no obvious discomfort in the patient after operation, and no daily life disorder and tumor recurrence were found in 2-year follow-up.
In general, this paper presents a rare case of giant solitary neurofibroma located in the groin area without NF-1 performance. It is a benign developing peripheral nerve tumor, and its pathogenesis is still unclear. Although the majority of neurofibromas have no discomfort symptoms at early stage, as they grow slowly, when they are too large or too deep, they can cause neurological symptoms or compression symptoms of adjacent organs just as what had happened in this patient, such as Tinel sign positive, and may also bring difficulty to operation and cause poor prognosis. Therefore, early diagnosis should be carried out to shorten the time interval between symptom appearance and treatment, which can be achieved by MRI and clinical manifestations. The confirmed diagnosis is through pathological sections. Except for the plexiform type, most of the tumors show good limitations, so the gold standard for the treatment of this disease is still surgery, especially in this case of large and isolated neurofibroma. Good prognosis and low recurrence rate are obtained after radical resection.