15.2 Bladder & Prostate

Bladder Technique and Normal Appearance

Transabdominal bladder sonography depends on a distended bladder as an acoustic window. Have the patient drink roughly 1 liter (about 32 ounces) of water 30-60 minutes before the examination and refrain from voiding. The full bladder displaces gas-filled bowel out of the pelvis and allows evaluation of the bladder wall, the distal ureters and ureterovesical junctions, the prostate, and the uterus and adnexa. Scan suprapubically in transverse and sagittal planes with a 2-5 MHz curvilinear transducer; reduce overall gain so the urine stays anechoic and subtle wall lesions are not washed out.

Normal urine is echo-free and the wall is thin and smooth. Bladder wall thickness should measure less than about 3 mm when the bladder is well distended and under roughly 5 mm when empty. This distention caveat matters: an underfilled bladder makes the wall appear spuriously thickened and can hide small lesions, while overdistention is uncomfortable and can trigger vasovagal symptoms. Before declaring wall thickening pathologic, confirm the bladder was adequately full. Document three orthogonal dimensions, wall character, any focal lesion with size and vascularity, and - when obstruction is suspected - the presence and symmetry of ureteral jets at the trigone with color Doppler. Trabeculation is a thickened, irregular, undulating wall produced by detrusor muscle hypertrophy from chronic bladder outlet obstruction - most often benign prostatic hyperplasia in men or a neurogenic bladder. With long-standing obstruction, small outpouchings called cellules develop between trabeculae and may progress to true diverticula.

Bladder Pathology

• Stones - echogenic, mobile foci that layer in the dependent portion of the bladder and usually cast an acoustic shadow; they may form around foreign bodies or suture material
• Diverticula - sac-like outpouchings through the detrusor; demonstrate the neck connecting the diverticulum to the lumen, watch it empty after voiding, and search inside for stones or tumor, since stagnant urine raises the risk of both. A Hutch diverticulum is a congenital type occurring adjacent to the ureterovesical junction, while most acquired diverticula arise from chronic outlet obstruction
• Cystitis - diffuse or focal wall thickening; emphysematous cystitis in diabetic patients shows echogenic gas foci with dirty shadowing or reverberation in the wall, while hemorrhagic cystitis fills the lumen with echogenic clot and debris. An indwelling catheter balloon appears as a round fluid-filled structure and should not be misread as a cystic mass
• Transitional cell carcinoma (TCC) - the most common bladder malignancy; appears as a fixed, polypoid or frond-like soft-tissue mass projecting into the lumen or as focal asymmetric wall thickening. TCC does not move with repositioning and often shows internal vascularity on color Doppler, features that separate it from mobile stones and avascular clot. Risk factors include smoking and industrial chemical exposure, and painless hematuria is the classic presentation

Post-Void Residual and Bladder Volume

Bladder volume is estimated with the prolate ellipse formula: length x width x height x 0.523, using the three maximal orthogonal dimensions. The post-void residual (PVR) is the volume remaining immediately after voiding. A PVR above roughly 100 mL is abnormal and suggests urinary retention from outlet obstruction, detrusor underactivity, or neurogenic bladder; serial PVR measurements are used to follow treatment. Measure quickly after voiding, because urine refills the bladder at 1-2 mL per minute. The same formula also estimates pre-void bladder volume when a protocol calls for documenting how full the bladder was during the pelvic survey.

Prostate

The prostate is assessed transabdominally through the distended bladder as a chestnut-shaped gland at the bladder base, inferior to the trigone and surrounding the proximal urethra. In benign prostatic hyperplasia (BPH), the transition (central) zone enlarges, producing a bulky, often heterogeneous gland. An enlarged median lobe protruding into the bladder base elevates the bladder floor and can mimic an intrinsic bladder mass - recognize its continuity with the prostate below. Prostate volume uses the same 0.523 formula; the normal gland is about 20-25 mL, and volumes above 30-40 mL indicate enlargement. The gland is divided into the central transition zone, the outer peripheral zone where most cancers arise, and a small central zone around the ejaculatory ducts. Transabdominal imaging estimates size and detects median-lobe protrusion and residual urine, but it cannot reliably exclude carcinoma; transrectal ultrasound (TRUS) provides the zonal detail needed to find the typically hypoechoic peripheral-zone tumors and to guide biopsy.

Ureteroceles

A ureterocele is a congenital cystic dilation of the distal submucosal ureter that balloons into the bladder at the ureterovesical junction. Sonographically it is a thin-walled, round cystic structure within the posterolateral bladder that may be seen to fill and empty as the ureter peristalses, producing the classic cobra-head appearance on contrast studies. In children, an ectopic ureterocele is strongly associated with a duplicated collecting system, where it drains the obstructed upper-pole moiety; the simple (orthotopic) type occurs in adults with a single system. Stones may form inside a ureterocele, and large ones can obstruct the bladder outlet or prolapse into the urethra. When a cystic structure is found at the trigone, always scan the ipsilateral kidney for duplication and hydronephrosis.