NBME Free 120 Membranous (NBME Answers)

NBME Free 120 Answers

free120/Block 3/Question#13 (reveal difficulty score)
A 32-year-old man is brought to the emergency ...
Membranous 🔍 / 📺 / 🌳 / 📖
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submitted by ∗bwdc(697)

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Blood at the meatus is the red flag (see what I did there?) for urethral injury, which should be evaluated for with a retrograde urethrogram. The membranous the most commonly injured by fracture. In contrast, the spongy urethra is most likely to be injured during traumatic catheter insertion or in a straddle injury.

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canyon_run Should we just assume that a pelvic fracture implies a membranous urethral injury? I was between membranous and spongy and I ended up choosing spongy because of the perineal bruising and fact that the patient was riding a motorcycle (and therefore susceptible to straddle injury). +1

bwdc Yes. You should think of spongy as the penile urethra, hence the predisposition to catheter-related trauma. +8

focus Diagram: https://www.earthslab.com/anatomy/urethra/ +1

topgunber it says no trauma to the penis so we have to rule out spongy. To tear the prostatic urethra would mean the prostate also got affected, which when compared to the vulnerable membranous urethra would be unlikely. Both spongy/prostatic urethra are vulnerable to TURP or catheter related trauma as mentioned. As far as the bladder itself and the intra-mural urethra, i would think fractures of the symphysis and above would cause that. +1

an1 "fracture of the superior pubic ramus" suggests that the anterior urethra is more likely damaged (prostatic and membranous; but proststaic is well protected). Also, if it was spongy (AKA bulbar) {part of the posterior urethra}, I'd want to see something about a scrotum filled with blood +

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submitted by ∗sugaplum(487)

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For reference FA 2019 pg 613 has a good image to see this

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jbrito718 UW qid 839 has ssimilar question and good explanation +1

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submitted by ∗avatar(17)

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Urethral injury: Occurs almost exclusively in males. Presents with blood at urethral meatus, hematuria, difficulty voiding. Urethral catheterization is relatively contraindicated. Anterior urethral injury—perineal straddle injury disruption of bulbar (spongy) urethra scrotal hematoma. If Buck fascia is torn, urine escapes into perineal space. Posterior urethral injury—pelvic fracture disruption at bulbomembranous junction, urine leakage into retropubic space and high-riding prostate. FA2021 page 651

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submitted by ∗jbrito718(48)

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According to UW qid:839 "The membranous segment is relatively unsupported by the adjacent tissues and is the weakest point of the posterior urethra. Trauma to the pelvis severe enough to cause fracture often results in disruption of the posterior urethra at the bulbomembranous junction." The presence of a pelvic fracture and presence of blood at the urethral meatus are key signs of urethral injury.

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