QUARTERLY BEAT / DECEMBER 2023 ///
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removal as they kept causing recurrent urethral obstruction. Uncommonly, blood clots can adhere to the wall and mimic neoplasia.
The agitated saline is instilled slowly into the bladder via a urinary catheter while the bladder is visualized real-time with ultrasound. Air bubbles admixed with fluid produce freely suspended intraluminal hyperechoic foci with variable ring-down artifact. Urinary bladder or proximal urethral rupture is confirmed if air bubbles are seen entering the adjacent pericystic peritoneal space. ARE THERE OBVIOUS INTRALUMINAL FOCI OR STRUCTURES IN THE URINARY BLADDER LUMEN? • Freely suspended or gravity-dependent intraluminal hyperechoic foci are very common in cats with urethral obstruction. Foci can be any combination of proteinaceous/cellular debris, crystals, small cystoliths, hemorrhage, and/or lipid droplets. Mineralized debris and small cystoliths quickly settle along the gravity-dependent wall and produce the distal acoustic shadowing artifact in the far field, especially when coalesced into clumps. Sometimes debris can adhere to the urinary bladder wall. A urinalysis can help clinicians determine the etiology of the debris. Serial POCUS can help evaluate whether or not intraluminal debris is decreasing in response to fluid diuresis and/or urinary bladder lavage. At this time, urinary bladder lavage does not appear to lower the risk for in-hospital recurrent urethral obstruction nor shorten the duration of catheter retention or hospitalization 11 . • Larger structures within the urinary bladder lumen are typically either cystoliths, blood clots, or masses. Similar to any other mineral structure, cystolithiasis will display a hyperechoic surface with varying distal acoustic shadowing. Newer ultrasound technologies such as compound imaging will both widen and decrease the degree of shadowing seen 12 . As a result, a lack of shadowing cannot be used to rule out stones, especially when they are small. The surface of uroliths may be smooth or rough. However, ultrasound may not be used to reliably predict stone composition. In the bladder, the adjacent colon can be confused with cystolithiasis. Changing the animal’s position during ultrasound (e.g., dorsal to standing) will easily distinguish the two as the colon will remain fixed in position and outside the urinary bladder while cystoliths will fall with gravity to the other side of the lumen. A small urinary bladder size can easily hide small cystoliths. Cystoliths may be incidental findings or associated with obstruction. In the case of the latter, uroliths may also be present in the urethra, ureters, and renal pelvis. Radiographs and/or a full diagnostic ultrasound should be performed if cystoliths are seen or suspected during POCUS. • The Blood clots can occur naturally with cystitis or immediately following cystocentesis. Blood clots typically appear as variably shaped and sized, smoothly marginated, heterogeneously hyperechoic mobile masses that often settle with gravity. Fortunately, blood clots usually resolve on their own with supportive care within 24-72 hours. Rarely, the author has witnessed large unresolving blood clots that required surgical
References
IS THE URINARY BLADDER WALL THICKENED? • Urinary bladder wall thickening may be focal, multifocal, or diffuse and is typically caused by cystitis. Blocked cats almost always have some degree of thickening due to sterile cystitis that occurs alone, or along with the presence of crystals or stones. Urinary infection in domestic short-haired cats < 10 years of age is uncommon but increases in frequency in older patients and some breeds. Cystitis often affects the ventral urinary bladder apex most severely. Rare causes of cystitis include polypoid cystitis, emphysematous cystitis, pseudomembranous cystitis, cystitis glandularis, and fungal cystitis. • Urinary bladder neoplasia is less common in cats as compared to dogs, especially as a cause of urinary obstruction. Male cats are overrepresented for bladder neoplasia. Like dogs, transitional cell carcinoma is most commonly diagnosed and appears ultrasonographically as a heterogeneously hyperechoic mass and/or focal or multifocal urinary bladder wall thickening with loss of normal wall layering. Cats are more likely to have masses in the mid-body rather than the trigone. Uncommonly reported tumors include lymphoma, fibrosarcoma, leiomyoma/sarcoma, adenocarcinoma, squamous cell carcinoma, hemangiosarcoma, rhabdomyosarcoma, and malignant peripheral nerve sheath tumors. Benign tumors of the urinary tract are rare and variable in etiology. IS THE URINARY CATHETER PROPERLY POSITIONED? • Once the patient is stabilized with urethral patency restored, serial POCUS exam can be used to confirm urinary catheter placement, trouble shoot malfunctioning urinary catheter, and monitor the patient’s response to therapy. Most urinary catheters appear as two parallel hyperechoic lines with an anechoic center. Catheters can easily be followed with POCUS to ensure they are not too long for the patient. If a urinary catheter stops producing urine, POCUS can be used to see if the catheter has changed position or if the tip is covered or surrounded by echogenic debris or blood clots. HOW IS THE PATIENT RESPONDING TO THERAPY? • Serial POCUS can be performed at a minimum of once a day to monitor the amount of peritoneal/retroperitoneal effusion, the degree of renal pelvic dilation, the size of the urinary bladder, and the location of the urinary catheter. Progressive peritoneal/retroperitoneal effusion in the face of a persistent or unresolved azotemia should raise concern for urinary rupture and prompt further diagnostics.
1. Beeston D and Cole L. Evaluation of the utility of point-of- care ultrasound in detecting ureteral obstruction in cats [abstract]. Ultrasound J. 2020;12(Suppl):45. 2. Boysen SR, Rozanski EA, Tidwell AS, et al. Evaluation of a focused assessment with sonography for trauma protocol to detect free abdominal fluid in dogs involved with motor vehicle accidents. J Am Vet Med Assoc 2004;225:1198- 1204. 3. Buckley C, Seitz MA, Wills RW, and Lee AL. Assessment of a standing position during abdominal point-of-care ultrasound on abdominal fluid score in dogs. J Vet Emerg Crit Care 2022. Accepted 6/30/2022. 4. Sislak MD, Spaulding KA, Zoran DL, et al. Ultrasonographic characteristics of lipiduria in clinically normal cats. Vet Radiol Ultrasound 2014;55(2):195-201. 5. Nevins JR, Mai W, and Thomas E. Associations between ultrasound and clinical findings in 87 cats with urethral obstruction. Vet Radiol Ultrasound 2015;56(4):439-447. 6. Liscandro GR, Lagutchik MS, Mann KA, et al. Evaluation of an abdominal fluid scoring system using abdominal focused assessment with sonography for trauma in 101 dogs with motor vehicle trauma. J Vet Emerg Crit Care 2009;19(5):426-437.
7. Gerken KK, Cooper ES, Bulter AL et al. Association of abdominal effusion with a single decompressive cystocentesis prior to catheterization in male cats with urethral obstruction. J Vet Emerg Crit Care 2020;30(1):11- 17. 8. Reineke EL, Cooper ES, Takacs JD, et al. Multicenter evaluation of decompressive cystocentesis in the treatment of cats with urethral obstruction. J Am Vet Med Assoc 2021;258(5):483-492. 9. Hall J, Hall K, Powell L, et al. Outcome of male cats managed for urethral obstruction with decompressive cystocentesis and urinary catheterization: 47 cats (2009- 2012). J Vet Emerg Crit Care 2015;25(2):256-262. 10. Griffin S. Feline abdominal ultrasonography…the kidneys and perinephric space. Journal of Feline Medicine and Surgery 2020;22:409-427. 11. Dorsey TI, Monagham KN, Repress M, et al. Effect of urinary bladder lavage on in-hospital recurrence of urethral obstruction and durations of urinary catheter retention and hospitalization for male cats. J Am Vet Med Assoc 2019;254(4):483-486. 12. Heng HG, Rohleder JJ, and Pressler BM. Associated acoustic shadowing artifacts in conventional vs. spatial compound imaging. Vet Radiol Ultrasound 2012;53(2):217- 220.
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