The prefix “retro-” in medical terminology is derived from the Latin word retro, which translates literally to “backward,” “behind,” or “in the past.” This linguistic root provides three distinct applications in medicine. This prefix serves to indicate a spatial relationship, describing the location of an anatomical structure relative to another. It also describes a directional concept, signifying movement that is reversed or against a normal path, or a sequence that refers to a prior state or time.
Retro as an Indicator of Anatomical Position
The most frequent application of “retro-” is to denote a static location situated behind a specific boundary or structure. This usage helps classify organs and tissues by their relationship to the body’s major cavities and membranes. For example, retrosternal describes a position directly behind the sternum (breastbone), a location where a growth or pain might be concerning due to its proximity to the heart and major blood vessels.
The retroperitoneal space is an important anatomical distinction, referring to the area of the abdominal cavity situated behind the peritoneum. The peritoneum is a large, thin membrane that lines the inner wall of the abdomen and covers most of the abdominal organs. Structures like the kidneys, adrenal glands, pancreas, and major blood vessels reside in this space. This separation is clinically significant because conditions here behave differently than those within the main peritoneal cavity, affecting surgical approaches and diagnostic imaging. Other positional terms include retrobulbar (behind the eyeball) and retrolental (behind the lens of the eye).
Retro as an Indicator of Direction or Flow
In contrast to static position, the prefix “retro-” can describe a dynamic process involving movement or flow that occurs in the reverse direction. The term retrograde literally means moving or going backward, often used to describe the flow of a bodily fluid or a nerve signal. For instance, retrograde ejaculation occurs when semen enters the bladder instead of exiting through the urethra, moving backward against the typical path of flow.
In the nervous system, a pain signal traveling from the extremities back toward the spinal cord is described as retrograde conduction. A common neurological example involving time is retrograde amnesia, which is the inability to recall memories formed before a specific event, such as a trauma or injury. This memory loss moves backward in time from the event, affecting past memories while the ability to form new ones remains intact. Retroflexion describes the bending or tipping of an organ backward, such as a retroflexed uterus tilted toward the rectum instead of forward toward the bladder.
Retro in Biological and Genetic Processes
The prefix also appears in terms describing biological processes that involve a reversal of the normal sequence or a prior developmental state. A prominent example is the retrovirus, a family that includes the human immunodeficiency virus (HIV). These viruses are named “retro” because they reverse the central dogma of molecular biology, which states that genetic information normally flows from DNA to RNA to protein.
Upon infecting a host cell, the retrovirus uses a specialized enzyme called reverse transcriptase to convert its viral RNA genome into a DNA copy. This newly created DNA then integrates itself into the host cell’s own DNA, essentially forcing the host to produce more viral particles. This action is a fundamental reversal of the typical flow of genetic information. Retroversion can describe the backward tipping of an organ (often the uterus) or a developmental concept where a structure reverts to a previous form.