N fossa cysts and small saphenous vein thrombosis are not difficult conditions, and I have never felt that there was any need to go through the trouble of identifying them, but some recent consultations and consultation cases have made me keep thinking about why this misclassification has occurred. This is a patient from a remote consultation. He had previously had varicose veins for many years and had not been concerned about them. Suddenly, one day, he developed pain in the posterior aspect of the N fossa, accompanied by a hard lump, which caused difficulty in walking, and went to the hospital where, after routine ultrasound and the doctor’s judgment, he was diagnosed as having a cyst in the N fossa, and was quickly scheduled for surgical treatment. Unfortunately, no cyst was found, but a somewhat adherent vascular mass, so the patient was left with a rather conspicuous S-shaped scar, but it turned out to be okay, and the patient was eventually relieved of the hidden danger in time, avoiding deep vein thrombosis, which in turn led to the consequences of pulmonary embolism. Some of my friends said that it is really undesirable to have a misdiagnosis of such a simple disease. I think the misjudgment of easy-to-diagnose diseases lies more in the problem of medical process. In fact, analyzing the whole medical process, we can find the crux of the problem. Although the principle of the onset of the two completely different, but in the clinical manifestations of very similar places. Appearance does have a similar place from the clinical manifestations of the disease onset of the location are located in the N fossa, this is the lower extremity anatomy is relatively complex place, when the cyst and thrombus in the volume of a relatively small time, embodied in the examination of the body are localized lumps or hard knots, the difference is that the cyst’s mobility is large, the thrombus mobility is small, and the emergence of thrombophlebitis after the skin and blood vessels are more tightly adhered to the skin, if the fat is thicker, the mobility is not enough. If the fat is thicker, the mobility is not precise enough to be judged only by the doctor’s experience, and it is easy to be guided by habit and to react first to a cyst in the N fossa. From the patient’s personal symptoms: N fossa cysts: N fossa area gradually swelling discomfort, accompanied by pain behind the knee, touch can reach the soft and have a certain elasticity of the swelling, some of the cysts can be compressed to impede the venous return, caused by the calf oedema, and even the formation of deep vein thrombosis. Small saphenous varicose vein with thrombus: early calf swelling and discomfort, weakness after walking, in the N fossa can be touched soft mass, can be deflated, after the formation of thrombus suddenly appeared N fossa of the hard knots, accompanied by pain, and with the surrounding soft tissues appear adherence, thrombus can spread to the deep veins. From the results of ultrasonography: N fossa cysts: usually present as a liquid dark area with clear borders. Small saphenous vein thrombosis: the initial ultrasound is a venous mass that cannot be deflated, and the soft tissues in the N fossa area are disorganized and not easy to distinguish after the appearance of adhesions. The key to avoid misjudgment: 1, patient communication to obtain comprehensive information: cysts generally exist for a long time, obvious in the knee joint extension position, and thrombus sclerosis is often a short period of time, which requires the doctor to communicate with the patient patiently, to obtain comprehensive information on the progress of the disease process. 2, strengthen communication between different specialties Ultrasound as an objective examination of the clinician to determine the disease is critical, in the vast majority of hospitals are not able to have a surgeon to carry out ultrasound in person under the conditions of ultrasound, ultrasound doctors and clinicians to communicate in a timely manner is necessary. An unavoidable fact The more links in the information transfer process, the more likely to be distorted. A must for optimizing the process and ultimately achieving precision medicine is a vascular surgeon with ultrasound skills.