A meniscal cyst is an outpouching of joint fluid, commonly seen near the lateral meniscus, caused by a tear within the meniscus, whereas neurofibroma is a nerve sheath tumor in the peripheral nervous system. Both have the capability to induce pain and create a focal mass.
A 37-year-old woman with no known disease had a lateral painless left-leg mass for 15 years. No examination had been performed to explore it. The mass spontaneously became painful 6 months before the visit. She felt pain night and day. The mass was under the left knee anterior to the head of the fibula. On examination, the mass measured 10 cm by 4 cm and was not pulsating (Figure 1A). There was no erythema, no articular limitation, and no neurological symptoms. The patient had not lost weight and had no fever. Magnetic resonance imaging (MRI) suggested a broken lateral meniscal cyst (Figure 1B). She underwent surgery by an orthopedic surgeon 1 month after the MRI. Bacteriological analyses were negative. Histopathologic examination revealed a benign neurofibroma.