Chapter 25 DETRUSOR MYOMECTOMY
Bladder augmentation has been used in a spectrum of clinical settings in which bladder dysfunction is refractory to more conservative treatment. Enterocystoplasty and gastrocystoplasty offer a reliable improvement in bladder compliance and capacity, decreased rates of upper urinary tract deterioration, and improved quality of life for patients. However, early and late complications related to incorporation of bowel segments in the urinary tract are many, cumulative, and well known. They include bowel contractions leading to incontinence, bowel obstruction, diarrhea syndromes, spontaneous perforation, abundant mucus production leading to stones, chronic bacteriuria, electrolyte imbalances, and the hematuria and dysuria syndrome (if a gastric segment is used).1–3 Use of bowel segments may also place the patients at risk for future malignancies.4,5
Detrusor myomectomy, also known as bladder autoaugmentation, is a simpler, less morbid alternative to enterocystoplasty. Autoaugmentation, as described by Cartwright and Snow6–8 in 1989, involves excising a portion of the detrusor muscle, allowing the bladder epithelium and lamina propria to form a large-mouthed bladder diverticulum. As the urothelium bulges through the muscular hiatus, bladder capacity is increased, intravesical storage pressures are reduced, and the volume at which a contraction occurs becomes larger. Because only bladder tissue is used in this technique, the risks associated with gastrointestinal segment incorporation into the urinary tract are obviated.
In patients with bladder dysfunction, the first line of treatment is anticholinergic medications, α-blocking agents, tricyclic antidepressants, and timed voiding or intermittent catheterization. Surgical intervention is appropriate when patients fail to respond clinically, develop upper tract compromise, or persistent compliance abnormalities. Video urodynamics is performed preoperatively for all patients to evaluate bladder storage and urethral continence function.9 The cystometric volume at an intravesical pressure of 40 cm H2O is recorded. In general, enterocystoplasty remains the better procedure for patients with poorly compliant, extremely small-capacity bladders because bladder capacity is increased to a lesser degree after detrusor myomectomy. However, detrusor myomectomy offers many advantages in certain patients in whom bowel complications would exacerbate comorbid conditions, including those who have had prior abdominal surgery, patients with bowel diseases, those with short gut or malabsorption syndromes, and those with prior episodes of peritonitis associated with ventriculoperitoneal shunts. We feel that myomectomy should be the first line of surgical therapy for idiopathic detrusor instability. Bladder autoaugmentation does not preclude a subsequent enterocystoplasty if it is necessary.
Patients with neuropathic lower urinary tract dysfunction require intermittent catheterization after myomectomy. Patients with idiopathic, non-neurogenic bladder contractile incontinence do not require intermittent catheterization after myomectomy. Patients with a low-compliance bladder related to radiation therapy or chemotherapy usually require intermittent catheterization after myomectomy.9,10 Selected patients are informed that a conventional enterocystoplasty can be performed if detrusor myomectomy is not a technical option intraoperatively. This option is discussed in detail before the operative date so that mechanical and antibiotic bowel preparation can be performed before surgery in these selected patients. Preoperative intravenous antibiotics are also administered.
The technique employed is modified from the original description by Cartwright and Snow.6–8 A two-way urethral catheter is placed so that bladder filling and emptying can be readily controlled, and a lower Pfannenstiel incision is made (Fig. 25-1). The rectus muscles are then separated in the midline, the prevesical space is entered (Fig. 25-2), and the dissection is continued until the bladder wall proper is cleared of adventitia (Fig. 25-3). Care is taken to sweep the peritoneum off the bladder dome. The bladder is then distended, and a no. 15 blade is used to carefully divide the detrusor muscle until the bladder mucosa protrudes from the muscle. A combination of gentle traction and sharp dissection is used to strip the entire detrusor muscle layer covering the dome and anterior wall, denuding the underlying bladder mucosa (Fig. 25-4