Ovarian cysts are relatively common, fluid-filled sacs that develop on an ovary, and most often, they cause no symptoms at all. When an ovarian cyst does cause pain, it is typically felt in the lower abdomen or pelvis, close to the affected ovary. The sudden appearance of pain in a distant area, such as the shoulder, can be confusing and raises immediate concern. This seemingly unconnected symptom is actually a telltale sign of an acute internal event. The anatomical link between the pelvis and the shoulder is an example of how the body’s nervous system can misinterpret the source of a distress signal.
How Ovarian Cysts Lead to Internal Irritation
Shoulder pain arising from an ovarian cyst is not caused by the cyst pressing on anything directly. This symptom only occurs when a complication forces pelvic contents to interact with structures higher up in the abdomen. This situation most often follows the sudden rupture of a cyst, which releases fluid, blood, or other irritants into the abdominal space. For example, a hemorrhagic cyst can burst and spill blood that irritates surrounding tissues.
A second, less common event is ovarian torsion, where the ovary twists on its supporting stalk. This twisting cuts off the blood supply, causing tissue death and releasing inflammatory substances into the abdominal cavity. In both rupture and torsion, the released substances flow upward. This fluid or blood eventually contacts the underside of the diaphragm, the large, dome-shaped muscle separating the chest from the abdomen.
Understanding Referred Pain and the Phrenic Nerve Connection
The mechanism that translates irritation of the diaphragm into pain felt in the shoulder is known as referred pain. This phenomenon occurs when the brain perceives pain as coming from a body part other than the one that is injured or inflamed. Here, the diaphragm is the structure physically irritated by the fluid or blood originating from the cyst.
The phrenic nerve is the sole nerve that provides motor function to the diaphragm, allowing us to breathe. Importantly, this nerve also carries sensory information from the diaphragm back to the central nervous system. The phrenic nerve originates high in the neck from the third, fourth, and fifth cervical spinal nerve segments, often abbreviated as C3, C4, and C5.
This is where the anatomical overlap occurs to create the shoulder pain. The same C3, C4, and C5 nerve segments that supply the diaphragm via the phrenic nerve also supply the sensory nerves to the skin and tissues of the shoulder region. When the diaphragm is irritated by the presence of blood or fluid, the phrenic nerve sends a strong pain signal to the spinal cord.
The brain receives this pain signal from the C3-C5 segments but is unable to distinguish the visceral origin (the diaphragm) from the somatic origin (the shoulder) that shares the same pathway. Because shoulder pain is a more common sensation, the brain misinterprets the signal, projecting the internal pain onto the surface of the shoulder. This referred pain is non-mechanical, meaning that moving the shoulder does not relieve or intensify the discomfort.
Associated Symptoms and When to Seek Immediate Care
The referred shoulder pain caused by an ovarian cyst complication is almost always accompanied by other, more localized symptoms. This specific combination of symptoms is a strong indicator that a medical emergency is occurring, such as significant internal bleeding or ovarian torsion. The initial symptom is usually the sudden onset of severe, sharp pain in the lower abdomen or pelvis, often localized to one side.
Other acute symptoms frequently include intense nausea and vomiting, as well as signs of internal blood loss. These signs may present as dizziness, lightheadedness, fainting, a rapid heart rate, or pallor. The presence of these systemic symptoms, particularly when combined with new-onset shoulder pain, requires immediate evaluation.
The shoulder pain, in this context, is a warning sign that the internal complication is progressing and irritating the upper abdominal cavity. If you experience sudden, severe pelvic pain accompanied by shoulder pain, fever, or signs of shock (such as dizziness or a racing heart), seek immediate emergency medical care. Prompt intervention is necessary to manage internal bleeding, prevent infection, or save the affected ovary.