Renal Calculus Pain (Ureteric/Renal Colic)

1. Terminology Clarification

"Renal colic" is actually a misnomer. The correct term is ureteric colic, because the pain arises from the ureter, not directly from the renal parenchyma. The two types of pain - renal pain and ureteric colic - are distinct:

Renal pain - caused by distension of the renal capsule. Felt as a constant, gnawing pain in the loin/renal angle.
Ureteric colic - caused by a stone (calculus) obstructing and distending the ureter. This is the typical, severe, colicky pain associated with kidney stones.

(Bailey and Love's Short Practice of Surgery, 28th Ed.)

2. Mechanism of Pain

When a stone passes from the renal pelvis into the ureter, it causes obstruction, which triggers two overlapping processes:

Ureteral distension - the backed-up urine distends the ureter proximal to the stone, stretching the ureteral wall. This activates visceral pain receptors (nociceptors) in the wall.
Peristaltic waves - the ureter continues its normal peristaltic contractions trying to push the stone past. These waves are superimposed on the distension, causing waves of intensifying then slightly easing pain. This gives renal colic its classic waxing-and-waning character.

The ureteric colic starts as soon as the stone enters the pelvi-ureteric junction and recurs at intervals for as long as the stone remains in the ureter. It ceases when the stone is expelled into the bladder or becomes completely impacted. (S. Das, Manual on Clinical Surgery)

3. Pain Radiation - Depends on Stone Location

The location of the pain and where it radiates tells you where the stone is:

Stone Position	Pain Character & Radiation
Pelvi-ureteric junction (PUJ) / upper ureter	Loin/renal angle, radiates toward groin. Sudden, griping. Patient writhes in agony with sweating and nausea.
Mid-ureter	Commences anteriorly just above the iliac crest; radiates along the genitofemoral nerve to the testis (male) or labium majus (female) and antero-medial thigh in both sexes. Testis may retract due to cremaster spasm.
Intramural ureter (near bladder)	Pain referred to the tip of the penis; patient complains of strangury (painful dribbling urination).
Impacted stone (any level)	Constant dull ache at the site of impaction, rather than colicky. Worsened by exercise, relieved by rest.

(S. Das, Manual on Clinical Surgery; Gray's Anatomy for Students)

4. Nerve Pathway - Why Pain Radiates

The mechanism of referred pain:

Visceral afferent (sensory) nerve fibers from the ureter enter the spinal cord at L1-L2 levels.
At these same spinal levels, somatic sensory nerves supply the skin of the loin, groin, scrotum/labia, and antero-medial thigh.
The brain misinterprets the visceral signal as coming from these somatic dermatomes - this is referred pain.
This explains why ureteric colic can radiate to the groin, testis, or thigh, but does NOT radiate to the back of the leg (which would indicate lumbar spine pathology).

(Gray's Anatomy for Students)

5. Key Clinical Features

Onset: Sudden, severe, griping pain - classically the patient cannot lie still and writhes/tosses in bed (unlike peritonitis, where patients lie still)
Character: Colicky - comes in waves, with partial relief between attacks
Associated features: Profuse sweating, nausea, vomiting, abdominal distension, haematuria (blood in urine)
Examination: Tenderness and rigidity along the course of the ureter; a stone in the lower ureter may be felt on rectal or vaginal examination
Important note: Right-sided upper ureteric colic can mimic appendicitis and must be differentiated

6. Distinguishing Renal Pain vs. Ureteric Colic

Feature	Renal Pain	Ureteric Colic
Cause	Renal capsule distension	Ureteric obstruction/spasm
Character	Constant, gnawing	Colicky, comes in waves
Location	Loin / renal angle	Lateralised, may radiate to groin/testis/labium
Radiation	Stays in loin	To groin, scrotum/labia, antero-medial thigh
Both together?	Yes - can occur simultaneously

Sources:

Bailey and Love's Short Practice of Surgery, 28th Ed., Chapter 81 (Urological Symptoms)
S. Das: A Manual on Clinical Surgery, 13th Ed., Diseases of the Ureter
Gray's Anatomy for Students, Case 8 - Ureteric Stone

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