Hourglass Uterus (Bandl's Ring / Pathological Retraction Ring)

Definition

Normal Retraction Ring vs. Pathological Ring

Mechanism / Pathophysiology

1. The UUS keeps retracting with each contraction, becoming shorter and thicker.
2. The LUS keeps stretching thin to accommodate the fetus.
3. The junction between them becomes exaggerated - forming Bandl's ring.
4. The fetus is caught in the constriction, with the head/body in the LUS below the ring and the fundus above.
5. If ignored, the LUS ruptures.

Causes (Why Obstruction Occurs)

• Cephalopelvic disproportion (CPD) - most common cause
• Malpresentations: brow, shoulder, face (mentoposterior), persistent occiput posterior
• Macrosomia
• Pelvic tumors or fibroids obstructing the birth canal
• Prolapsed cord or arm
• Neglected/prolonged labor (incidence ~0.02%, or 1 in 5,000 live births)

Clinical Features

• Severe, continuous lower abdominal pain (uterus may not relax between contractions)
• An oblique groove palpable/visible across the abdomen - the classic hourglass sign
• The groove rises toward the umbilicus as obstruction worsens (sign of imminent rupture)
• Tenderness over the lower uterine segment
• Signs of maternal distress: tachycardia, dehydration, exhaustion
• Full bladder (may obstruct), hematuria if bladder involved
• Lack of progress despite strong contractions (secondary uterine inertia may follow)

• Fetal distress (CTG changes - late decelerations, bradycardia)
• Caput succedaneum, moulding of the head
• Infant mortality rate reported >50% if not promptly managed

Diagnosis

• Primarily clinical: history of obstructed/prolonged labor + palpable oblique groove
• Ultrasound: confirms distorted uterine anatomy, shows the constriction ring, assesses fetal compromise and position
• Bimanual examination: may reveal a soft, large cervix with an hourglass-shaped uterus

Management

Emergency - time-sensitive situation

Immediate Steps:

1. Call for help - senior obstetrician, anesthetist, neonatologist
2. IV access, resuscitation fluids, Foley catheter
3. Continuous fetal monitoring
4. Do NOT use oxytocin or misoprostol - uterine stimulation is absolutely contraindicated (risks immediate rupture)
5. Do NOT attempt instrumental vaginal delivery (forceps/ventouse) - also contraindicated

Definitive Treatment:

• Emergency Cesarean section (LSCS) - the only safe option
• During cesarean, the constriction ring may trap the baby's head in the lower segment - the surgeon must digitally dilate or incise the ring to deliver the baby
• Nitroglycerin (sublingual or IV) or halothane anesthesia can temporarily relax the ring intraoperatively to facilitate delivery
• If uterine rupture has occurred: repair vs. hysterectomy depending on extent

Postoperative:

• Watch for PPH (uterine atony after prolonged labor)
• Antibiotics (infection risk from obstructed labor)
• Neonatal resuscitation team on standby

Complications if Untreated

Key Exam Points (Summary)

• Hourglass uterus = Bandl's pathological retraction ring = sign of obstructed labor and imminent uterine rupture
• The groove rises obliquely and climbs toward the umbilicus
• Oxytocin is absolutely contraindicated
• Treatment = emergency cesarean section
• Incidence: ~1 in 5,000 live births (IJRCOG comprehensive review)
• Infant mortality >50% without prompt intervention (PMC simulation study)