N fossa cysts and small saphenous vein thrombosis are not difficult conditions and have never felt the need to go to great lengths to identify them, but some recent consultations and office visits have kept me thinking about why this miscalculation occurred. This is a patient from a remote consultation. He had had varicose veins for many years previously and had not been concerned about them. Suddenly one day he developed pain behind the N fossa with a hard lump that caused difficulty walking and went to the hospital where, after routine ultrasound and doctor’s judgment, he was diagnosed with an N fossa cyst and was quickly scheduled for surgery. Unfortunately, the cyst was not found, but a somewhat adherent vascular mass, so the patient was left with a rather conspicuous S-shaped scar, but the result was fortunate, and the patient was eventually relieved of the hidden problem in time to avoid the consequences of deep vein thrombosis, which in turn led to pulmonary embolism. It is reasonable to say that a misdiagnosis of such a simple disease should not have occurred. The misdiagnosis of an easily diagnosed disease lies more in the problem of the medical consultation process, in fact, the analysis of the entire consultation process can reveal the crux of the problem. Although the principles of pathogenesis are completely different, there are similarities in the clinical manifestations of the two diseases. When the cyst and thrombus are relatively small in size, they are both localized lumps or hard nodules, but the difference is that the cyst is more mobile and the thrombus is less mobile. If the fat is thicker here, the mobility is not precise enough, and judging only from the doctor’s experience, it is easy to be guided by habit and the first reaction is N-fossa cyst. From the patient’s personal symptoms: N-fossa cyst: the N-fossa area gradually becomes swollen and uncomfortable, with pain behind the knee, soft and elastic swelling can be reached by touch, and some of the cysts can compress and obstruct the venous reflux, causing calf edema and even the formation of deep vein thrombosis. Saphenous varicose vein with thrombosis: early swelling and discomfort in the calf, weakness after walking, soft masses can be touched out of the N fossa, which can be pressed and deflated, and after the formation of thrombosis, a hard node of the N fossa suddenly appears, accompanied by pain and adhesion with the surrounding soft tissues, and the thrombosis can spread to the deep vein. From the results of ultrasonography: N fossa cyst: generally liquid dark area with clear border. 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 after the appearance of adhesions, which is not easy to distinguish. The key to avoid misjudgment: 1.Patient communication to obtain comprehensive information Cysts usually exist for a long time and are obvious in the knee joint extension position, while hard nodes of thrombosis often appear in a short time, which requires doctors to communicate patiently with patients to obtain comprehensive information about the disease progression process. 2.Strengthening communication between different specialties Ultrasound as an objective examination is essential for clinicians to determine the disease. In the vast majority of hospitals, where surgeons are not yet available to perform ultrasound in person, timely communication between ultrasonographers and clinicians is necessary. 3. An unavoidable fact The more links in the information transmission process, the easier it is to distort. The necessary condition for optimizing the process of medical treatment and finally achieving precise medical treatment is a vascular surgery specialist with ultrasound technology.