NAVLE Reproductive

Equine Patent Urachus Study Guide

📅 March 28, 2026 ⏱ 25 min read

Patent urachus is one of the most common umbilical abnormalities in neonatal foals, occurring at a frequency of approximately 7.8% of all foals up to 14 days of life.

Overview and Clinical Importance

Patent urachus is one of the most common umbilical abnormalities in neonatal foals, occurring at a frequency of approximately 7.8% of all foals up to 14 days of life. This condition represents the failure of the urachus (the fetal conduit connecting the bladder apex to the umbilicus for urine drainage into the allantois) to close properly at birth.

The urachus normally fibroses and regresses after parturition, becoming the median (middle) ligament of the bladder. When this closure fails, urine continues to leak from the umbilicus, creating a moist environment that predisposes to bacterial infection and potentially life-threatening complications including septicemia, septic arthritis, and pneumonia.

Structure	Fetal Function	Adult Remnant
Urachus	Drains fetal urine from bladder to allantoic cavity	Median (middle) ligament of bladder
Umbilical Vein (1)	Carries oxygenated blood from placenta to fetus	Round ligament of liver (falciform ligament)
Umbilical Arteries (2)	Carry deoxygenated blood from fetus to placenta	Round ligaments of bladder

Anatomy of the Fetal Umbilical Structures

The equine umbilical cord contains four clinically important structures that undergo involution after birth:

High-YieldThe urachus is located BETWEEN the two umbilical arteries and runs from the bladder apex to the umbilicus. Bladder rupture in foals most commonly occurs at the junction of the urachus and bladder apex.

Type	Definition	Timing
Persistent Urachus	Urachus fails to close at birth (congenital)	Immediately after birth
Patent Urachus	Urachus closes initially but reopens (acquired)	Usually 7-14 days postpartum

Etiology and Pathophysiology

Types of Urachal Patency

NAVLE TipAcquired patent urachus (91.1%) is MORE COMMON than persistent urachus (8.9%). Acquired cases are typically associated with underlying infection or systemic illness.

Risk Factors

Risk Factor Category	Specific Examples
Umbilical Cord Abnormalities	Excessive cord length (greater than 84 cm), partial torsion, premature cord rupture
Increased Abdominal Pressure	Meconium impaction/straining, partial urethral obstruction, lifting foal under abdomen
Foal Health Status	Prematurity, weakness, immunocompromised, prolonged recumbency, systemic illness
Infection	Omphalitis (80% of patent urachus cases have concurrent omphalitis)
Sex Predisposition	Colts more commonly affected than fillies (74.3% vs 25.7%)

Clinical Signs and Presentation

The hallmark clinical sign is urine leakage from the umbilicus. The degree of leakage varies:

Mild: Persistently moist umbilical stump (100% of cases)
Moderate: Visible urine dripping during micturition (75% of cases)
Severe: Full stream of urine from umbilicus, continuous leakage

Secondary Clinical Findings

Urine scald dermatitis: Irritated skin around umbilicus and inner thighs
Umbilical enlargement: Thickened, swollen stump suggests concurrent omphalitis
Pain on palpation: Indicates infection/inflammation
Purulent discharge: Confirms bacterial infection

Exam Focus: Average age at diagnosis is 5.5 days. A patent urachus in a 1-2 week old foal typically indicates the foal is systemically ill - treat the underlying illness!

Structure	Normal	Abnormal Findings
Umbilical vein	Less than 1.0 cm	Enlargement, hyperechoic content
Umbilical arteries	Less than 1.0 cm each	Asymmetry, abscessation
Urachus + arteries complex	Less than 2.5 cm at bladder apex	Greater than 2.5 cm = infection

Diagnostic Approach

Diagnosis is usually straightforward based on visual observation of urine leaking from the umbilicus.

Ultrasonographic Examination

Transabdominal ultrasound is the gold standard diagnostic tool with 96.6% sensitivity. Equipment: 6-10 MHz linear probe (7.5 MHz optimal).

Normal Ultrasound Measurements

Pathognomonic finding: Anechoic fluid within the urachus continuous with bladder apex and external umbilicus.

NAVLE TipThe urachus is the MOST COMMONLY infected umbilical structure. However, umbilical VEIN infections with secondary hepatic abscessation represent the most SEVERE abnormality.

Laboratory Evaluation

CBC: Often unremarkable; leukocytosis suggests infection
Fibrinogen: Elevated in infection; monitor for treatment response
Lactate: Elevated on admission = significantly worse prognosis
IgG: FPT increases risk of complications (IgG less than 800 mg/dL = FPT)
Blood/Umbilical Culture: Common: E. coli, Streptococcus, Enterococcus, anaerobes

Scenario	Treatment	Notes
Simple, no infection, lumen less than 6mm	Medical: antibiotics + topical care	Many close spontaneously
No improvement after 5-7 days	Surgical resection	Referral to surgical facility
Large lumen (greater than 6mm) or sepsis	Early surgical intervention	Better prognosis with early surgery

Treatment

Treatment Decision Algorithm

Antimicrobial Therapy

Local Care

Umbilical dipping: Chlorhexidine (0.5%) or dilute iodine 2-3 times daily
Barrier cream: Petroleum jelly to prevent urine scald

CRITICAL: Silver nitrate cauterization is NO LONGER RECOMMENDED - may predispose to infection. CONTRAINDICATED when local sepsis is present (risk of urachal rupture and uroperitoneum).

Surgical Indications

Large urachal lumen (greater than 6 mm)
Umbilical infection (omphalitis, omphalophlebitis)
Sepsis
No improvement after 5-7 days of conservative treatment

Procedure: Umbilical remnant resection via ventral midline celiotomy under general anesthesia. Includes resection of urachus with partial cystectomy. Survival rates: 77-91% depending on technique.

Drug	Dose	Route/Freq	Notes
Gentamicin + Penicillin	6 mg/kg + 15-20k IU/kg	IV q24h + IV q6h	First-line for septic foals
Ceftiofur	5 mg/kg	IV q12h	3rd gen cephalosporin
TMS	35 mg/kg total	PO/IV q12-24h	Good for uncomplicated; NOT for abscesses

Complications and Prognosis

Prognosis Summary

Simple persistent urachus: EXCELLENT - most close spontaneously
Acquired with early treatment: GOOD - 67% discharge rate; 89% with surgery
Advanced infection with septicemia: GUARDED to POOR (~30% survival)

Complication	Mechanism	Prognosis Impact
Septic Arthritis/Physitis	Hematogenous spread to joints	OR 33 for non-survival - MOST significant negative factor
Hepatic Abscess	Extension of umbilical vein infection	Poor (~30% survival)
Uroperitoneum	Urachal rupture	Emergency; requires surgery
Incisional Hernia	Post-surgical	18.5% of surgical cases

Prevention

Allow natural cord separation (at natural constriction ~5 cm from body wall)
Proper umbilical care: Dip navel in chlorhexidine at birth and several times over first 24 hours
Ensure adequate colostrum: Verify IgG greater than 800 mg/dL by 12-24 hours
Monitor umbilicus daily for moisture, enlargement, discharge
Prevent straining: Monitor for and treat meconium impaction promptly

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