Kidney stones are hard deposits formed from concentrated minerals and salts that develop inside the kidneys. When these deposits move out of the kidney and become lodged in the urinary tract, they cause severe pain known as renal colic. While this pain is typically associated with the back and side, some individuals feel this discomfort deep within the pelvis, sometimes presenting as rectal pain. This article explores the physiological mechanism connecting a stone in the urinary system to discomfort felt in the rectal area.
Referred Pain and the Connection to Rectal Discomfort
The sensation of rectal discomfort originating from a kidney stone is known as referred pain, where the brain misinterprets nerve signals. Referred pain occurs because internal organs, which have limited sensory nerves, share common neural pathways with various surface areas of the body. The ureters—the tubes that carry urine from the kidneys to the bladder—are innervated by a complex network of nerves.
When a kidney stone travels down the ureter, particularly as it reaches the lower portion near the bladder, the stone causes distension and irritation of the ureteral wall. This irritation triggers strong pain signals that travel up to the spinal cord. The nerves supplying the ureters share common sensory roots with nerves that supply the groin, genitals, and deep pelvic structures, including the rectum.
Because the pain messages from the ureter and the rectum converge at the same spinal cord segments, the brain struggles to accurately pinpoint the source. It often interprets the visceral signal from the ureter as originating from the more common nerve endings in the pelvis. For this reason, a stone lodged low in the ureter can be perceived as a vague, deep ache or localized pain in the rectal area. This discomfort is directly related to the stone’s movement and the resulting spasms of the ureteral smooth muscle.
Common Locations of Kidney Stone Pain
To understand the referred rectal discomfort, it is helpful to know the typical progression of kidney stone pain, known as renal colic. The pain usually begins in the flank, the area on the side and back just below the ribs. This initial pain is caused by the stone obstructing urine flow, leading to increased pressure and stretching of the kidney capsule.
As the stone moves down the ureter, the location of the pain often shifts and radiates forward. The discomfort commonly travels from the flank, across the abdomen, and down toward the groin. In males, the pain may be felt in the testicle on the same side as the stone, illustrating the principle of referred pain along shared nerve pathways.
The pain associated with renal colic is frequently described as one of the most severe types of pain a person can experience. It is sharp, cramping, and intermittent, coming in intense waves that can last for several minutes at a time. This spasmodic nature distinguishes the pain of a kidney stone from a duller, more constant backache.
When Rectal Pain Requires Immediate Attention
While referred rectal discomfort can be a sign of a kidney stone, this area can also signal other serious, unrelated conditions. Any persistent or severe rectal pain should be evaluated by a medical professional to ensure a correct diagnosis, especially if accompanied by “red flag” symptoms that suggest an infection or a complication.
If the rectal pain is accompanied by a fever and chills, it may indicate that urinary tract obstruction has led to a serious kidney infection. This combination requires immediate attention and treatment. Severe, continuous nausea and vomiting or an inability to pass urine should also prompt an urgent visit to the emergency room.
Rectal pain can also be caused by local issues such as abscesses, anal fissures, or thrombosed hemorrhoids. If the discomfort includes significant rectal bleeding, the passage of pus or discharge, or the inability to pass gas or stool, a different underlying cause must be considered. Regardless of a known history of kidney stones, a medical professional must confirm the true source of the discomfort and rule out alternative diagnoses.