Clinical overview
Acute pelvic pain is one of the most common reasons women present to emergency departments and to gynaecology assessment units. The clinical task — distinguishing a life-threatening surgical emergency from a benign, self-limiting process — depends entirely on understanding why the pain exists. Pain mechanism dictates pain quality, distribution, time course, and the constellation of associated signs. A registrar who can map the symptom onto the underlying pathophysiology can triage confidently with a hand on the abdomen and a focused history, before any investigation returns.
The genital tract shares its visceral innervation, peritoneal coverage, and pelvic location with the urinary tract and lower bowel. This anatomical promiscuity is why "pelvic pain" is rarely purely gynaecological at the bedside — appendicitis, ureteric colic, diverticulitis, and irritable bowel can all masquerade as gynaecological pain, and vice versa. The chapter focuses on gynaecological mechanisms, but you must always hold the non-gynaecological differential in mind.
There are four dominant pathophysiological mechanisms producing acute gynaecological pelvic pain: (1) acute distension or rupture of a hollow viscus or capsule (ovarian cyst rupture, ectopic, ovarian torsion, haemoperitoneum); (2) acute inflammation with peritoneal involvement (PID, tubo-ovarian abscess, endometriosis flare); (3) ischaemia (torsion, infarcted fibroid, ovarian vein thrombosis); and (4) myometrial or cervical activity (miscarriage, labour pain in early gestations, dysmenorrhoea). Each of these has a characteristic pain footprint that you should learn to recognise.
Core knowledge
Pelvic visceral innervation — why the pain feels the way it does
The pelvic organs receive autonomic supply from the inferior hypogastric (pelvic) plexus, with parasympathetic input from S2–S4 (nervi erigentes) and sympathetic input from T10–L2 via the hypogastric nerves. Visceral afferents travel with the sympathetic fibres, so pain from the uterus and adnexa is referred to T10–L1 dermatomes — the suprapubic region, lower abdomen, and inner thigh. The ovary in particular, because of its midline embryological origin and ovarian vessel supply, refers pain to the periumbilical region (T10), which is one reason ovarian torsion is so often mistaken for early appendicitis.
The cervix is an exception: its pain is parasympathetically mediated and refers to the sacral dermatomes, producing the characteristic deep, dragging, low-back-radiating pain of cervical motion tenderness in PID or of an incomplete miscarriage with cervical dilatation.
Once the inflammatory process touches the parietal peritoneum, somatic innervation takes over: pain becomes sharp, well localised, and exacerbated by movement, cough, and palpation. This is the transition that turns a vague visceral pain into a "surgical abdomen" and is the single most important physical-sign transition to recognise.
Acute capsular distension and rupture
Rupture spills blood into the pouch of Douglas and irritates peritoneum, with diaphragmatic irritation causing shoulder-tip pain.
The ovarian cortex has a tough fibrous capsule under tension as a follicle or cyst enlarges. Visceral afferents in the capsule fire in response to stretch. The pain of a slowly enlarging functional cyst is dull and chronic; the pain of rupture is sudden, sharp, and often referred to one iliac fossa, coinciding precisely with the moment of capsule disruption. Free fluid then irritates the peritoneum (somatic pain), producing rebound and guarding. If the cyst is haemorrhagic, ongoing bleeding into the peritoneal cavity produces shoulder-tip pain via diaphragmatic (C3–C5, phrenic) irritation — a clue you should specifically ask about.
The classic ruptures: corpus luteum cyst at mid-luteal phase (often with Ectopic pregnancy management as differential because of the timing in early pregnancy), endometrioma (chronic dull pain becoming acute and severe with often dramatic peritoneal signs because endometriotic fluid is intensely irritating), and follicular cyst (mid-cycle pain — Mittelschmerz — which is physiological release of follicular fluid).