What causes the Christmas tree bladder on cystography?
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Answer:
The Christmas tree or pine cone bladder is an elongated, vertically orientated bladder with a serrated, scalloped outline and a raised, narrowed bladder neck, described on cystography, voiding cystourethrography and CT or MR cystography. It is the classic appearance of the neurogenic bladder with detrusor-sphincter dyssynergia, seen in spinal cord injury, spina bifida and multiple sclerosis. The important associated findings, which are what the imaging is really for, are trabeculation, sacculation and diverticula from sustained high intravesical pressure, a thick-walled bladder of reduced compliance, vesicoureteric reflux, hydroureteronephrosis and, over time, renal scarring and failure. Stones form in the stagnant bladder and around catheters, and chronic catheterisation and infection carry a small long-term risk of squamous cell carcinoma. Imaging is complementary to video-urodynamics, which measures detrusor pressure, compliance and leak point pressure and identifies the patients whose upper tracts are at risk, defined by a detrusor leak point pressure above about 40 cmH₂O. The differential for a trabeculated, elongated bladder is chronic bladder outlet obstruction from prostatic enlargement or urethral stricture, which produces a similar wall response without the neurological history, and the two may coexist.
Why is it called so?
The tapering, serrated bladder outline resembles a Christmas tree or a pine cone.
Pathophysiology
When the spinal cord lesion lies above the sacral micturition centre, reflex detrusor contraction is uninhibited and the external sphincter contracts simultaneously instead of relaxing, which is detrusor-sphincter dyssynergia. The detrusor contracts against a closed outlet, generating very high intravesical pressures. The muscle hypertrophies and its bundles become prominent, producing trabeculation, and mucosa herniates between them to form saccules and diverticula, which gives the serrated contour. Sustained high storage pressure is transmitted to the ureters, overcoming the antireflux mechanism, so reflux and hydronephrosis develop and the kidneys are progressively damaged. Preserving renal function by lowering storage pressure, with anticholinergics, botulinum toxin, clean intermittent catheterisation or augmentation, is therefore the goal of management.
Alternative names: Pine cone bladder; fir tree bladder
Other associated named signs: Spinning top urethra in dysfunctional voiding and the trabeculated bladder of chronic outlet obstruction
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