A disc protrusion is a medical condition that can occur in some

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s, including humans, in which the outermost layers of the ''anulus fibrosus'' of the

intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...

s of the spine are intact but bulge when one or more of the discs are under pressure. Many disk abnormalities seen on

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

that are loosely referred to as "

herniation A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin herni ...

" are actually just incidental findings. These may be unrelated to any symptoms and are just bulges of the ''anulus fibrosus''. Jensen and colleagues, in an MRI study of the

lumbar spine The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...

in 98 ''asymptomatic'' adults, found that in more than half, there was a symmetrical extension of a disc (or discs) beyond the margins of the interspace (bulging). In 27 percent, there was a focal or asymmetrical extension of the disc beyond the margin of the interspace (protrusion), and in only 1 percent was there more extreme extension of the disc (extrusion or sequestration). These findings emphasize the importance of using precise terms in describing the imaging abnormalities and evaluating them strictly in the context of the patient's symptoms.Ropper AH, Samuels MA, Klein JP. Chapter 11. Pain in the Back, Neck, and Extremities. In: Ropper AH, Samuels MA, Klein JP. eds. Adams & Victor's Principles of Neurology, 10e. New York, NY: McGraw-Hill; 2014. http://accessmedicine.mhmedical.com.eres.library.manoa.hawaii.edu/content.aspx?bookid=690&Sectionid=45424419. Accessed September 29, 2015. A disc protrusion may progress to a

spinal disc herniation Spinal disc herniation is an injury to the cushioning and connective tissue between vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, and physical ...

, a condition in which there is a tear in the ''anulus fibrosus''.

References

Bones of the vertebral column {{musculoskeletal-disease-stub