This term is applied to a cyst filled with a clear colourless jelly or colloid material, met with in the vicinity of a joint or tendon sheath.

The commonest variety—­the carpal ganglion—­popularly known as a sprained sinew—­is met with as a smooth, rounded, or oval swelling on the dorsal aspect of the carpus, usually towards its radial side (Fig. 60).  It is situated over one of the intercarpal or other joints in this region, and may be connected with one or other of the extensor tendons.  The skin and fascia are movable over the cyst.  The cyst varies in size from a pea to a pigeon’s egg, and usually attains its maximum size within a few months and then remains stationary.  It becomes tense and prominent when the hand is flexed towards the palm.  Its appearance is usually ascribed to some strain of the wrist—­for example, in girls learning gymnastics.  It may cause no symptoms or it may interfere with the use of the hand, especially in grasping movements and when the hand is dorsiflexed.  In girls it may give rise to pain which shoots up the arm.  Ganglia are also met with on the dorsum of the metacarpus and on the palmar aspect of the wrist.

[Illustration:  FIG. 60.—­Carpal Ganglion in a woman aet. 25.]

The tarsal ganglion is situated on the dorsum of the foot over one or other of the intertarsal joints.  It is usually smaller, flatter, and more tense than that met with over the wrist, so that it is sometimes mistaken for a bony tumour.  It rarely causes symptoms, unless so situated as to be pressed upon by the boot.

Ganglia in the region of the knee are usually situated over the interval between the femur and tibia, most often on the lateral aspect of the joint in front of the tendon of the biceps (Fig. 61).  The swelling, which may attain the size of half a walnut, is tense and hard when the knee is extended, and becomes softer and more prominent when it is flexed.  They are met with in young adults who follow laborious occupations or who indulge in athletics, and they cause stiffness, discomfort, and impairment of the use of the limb.  A ganglion is sometimes met with on the median aspect of the head of the metatarsal bone of the great toe and may be the cause of considerable suffering; it is indistinguishable from the thickened and enlarged bursa so commonly present in this situation in the condition known as bunion.

[Illustration:  FIG. 61.—­Ganglion on lateral aspect of Knee in a young woman.]

Ganglionic cysts are met with in other situations than those mentioned, but they are so rare as not to require separate description.

Ganglia are to be diagnosed by their situation and physical characters; enlarged bursae, synovial cysts, and new-growths are the swellings most likely to be mistaken for them.  The diagnosis is sometimes only cleared up by withdrawing the clear, jelly-like contents through a hollow needle.