Ultrasonography-guided, fine-needle aspiration in three dogs with transitional cell carcinoma of the bladder, urethra, and prostate gland, respectively, caused development of tumor masses along the needle track 8 weeks to 8 months later. Needle size was 22 gauge in two dogs and 18 gauge in the third. This problem has been reported rarely in human medicine, and it is not known how common it is in dogs. The authors currently recommend that cytologic specimens of suspected transitional cell carcinoma be obtained by traumatic catheterization, whereby fluid is aspirated through a catheter adjacent to the lesion after the mass has been vigorously manipulated.

COMMENTARY: Development of tumor masses along the needle track after ultrasonography-guided aspiration in transitional cell carcinoma may become more apparent as more effective treatments of transitional cell carcinoma prolong life. The relative merits of fine-needle aspiration and traumatic catheter aspiration to obtain cytologic samples are not known.

Needle-tract implantation following US-guided fine-needle aspirate of transitional cell carcinoma of the bladder, urethra and prostate. Nyland TG, Wallack ST, Wisner ER. Vet Radiol Ultrasound 43:50-53, 2002.