The glomus body and its tumors:

The glomus body is a unique receptor or rather a thermal sensor found mainly in the dermis of the skin. This is a strange kind of tissue, microscopic in size but with a very important function, somewhat akin to the sensors found inside the room air conditioner. It acts as a sensor detecting changes in temperature of the environment and passes this information up the nervous system resulting in shunting of blood away from the skin by vasoconstriction (shrinking the diameter of the capillaries in the skin) when the surroundings turn cool. This simple mechanism prevents loss of heat during the winter and cool weather. The opposite happens during warm weather. Perhaps we don't realize the importance of these tiny nodes in the skin until it malfunctions. Perhaps the most common pathology of this node is in the distal part of the fingers- the subungual region (the part between the finger nail and the underlying phalanx or bone). This condition is the glomus tumor, a very vascular growth, some call it a hamartoma of the glomus body.
See- http://www.ultrasound-images.com/musculoskeletal.htm , where I discuss this pathology in detail with color Doppler and ultrasound imaging of this rather poorly understood and still relatively unexplored pathology. 

 The grey scale B-mode ultrasound image above shows a typical glomus tumor, seen as a hypoechoic, soft tissue mass beneath the fingernail.

 

The color Doppler image above shows the vascular nature of the subungual glomus tumor in the 2nd finger.Note the erosion of the underlying bone. Both above images are courtesy of Shlomo Gobi, Israel.