Osseous metaplasia

A 40-year-old male with history of gonococcal urethritis 20 years ago presented with repeated episodes of dysuria and urinary stream thinning for nearly 10 years. The clinical diagnosis was urethral stricture with calculi formation. Segmental resection of urethral stricture and end to end anastomosis were performed. Postoperative pathologic examination revealed multiple submucosal focal deposition of calcium salts with osseous metaplasia. Urethral osseous metaplasia is extremely rare and chronic inflammatory may caused reactive bone formation in suburothelium.

Authors: Wang, Yongquan ; Song, Siji; Xiong, Enqing
Corresponding Author: Wang, Yongquan

Introduction
Anterior urethral stricture is not rare, and is usually due to repeated chronic inflammation, stones or catheterization. However, anterior urethral stricture with osseous metaplasia is extremely rare. Here we present a male patient with 10-year-repeated dysuria; the clinical impression was of anterior urethral stricture with calculi, but histopathologic features revealed osseous metaplasia within the urethra.

Case report
A 40-year old male consulted our centre for assessment of a 10-year history of repeated dysuria and urinary stream thinning. He had received prior urethral dilatation treatment. He suffered from gonococcal urethritis 20 years ago, which had been managed with medical treatment for 1 month (he could not remember in detail). Physical examination found palpable hard stenosis in the penile urethra. The results of urine culture were negative. Gonococcus smear in urethral secretions was negative. Tuberculosis was also excluded by purified protein derivative test (PPD), urine polymerase chain reaction (PCR) and serum anti-tuberculosis antibody detection. Pelvic X ray radiography and voiding cystourethrography demonstrated an anterior urethra stricture and half-arc shaped high density image (Figure 1). The clinical diagnosis of urethral stricture with calculus formation was made. Endourethral treatment with a ureteroscope attempting to push the calculus back into the bladder failed, because the ureteroscope could not pass through and there was no obvious stone inside the urethral lumen. Segmental resection of the urethral stricture and end to end anastomosis were performed. During the operation, a bone-like mass was palpated within the urethra, which was impacted and closely connected with the urethral mucosa (Figure 2). The length of stricture segment was about 2 cm. Postoperative pathologic examination revealed multiple submucosal focal deposits of calcium salts with osseous metaplasia (Figure 3 A and B ). Alizarin red staining indicated extensive calcium nodules and ossification (Fig3 C and D). After indwelling catheterisation for 2 weeks, the patient urinated satisfactorily and had no other problems at 6 month follow-up.

Discussion
Osseous metaplasia in the male urogenital system is uncommon and occasionally reported in urinary tumours or ureteral amyloidosis [1-3]. Urethral osseous metaplasia has never been reported in literature, so far as we are aware. Chronic infection stimulates the proliferation of mesenchymal cells that have inherent properties of metaplasia and can differentiate into chondroblasts or osteoblasts [4,5]. Urethral osseous metaplasia is an extremely rare event and the gonococcal infection history may relate to the pathological changes in this case. Although very rare, osseous metaplasia need to be distinguished from calculi. Patients with urethral osseous metaplasia have relatively long-term history, negative results of urine analysis and no obvious stone visualized endoscopically.

Conclusion
Anterior urethral osseous metaplasia is extremely rare. Pathologists and urologists should be aware of this kind of uropathy. We recommend open operation treatment for urethral osseous metaplasia, rather than urethral dilatation and endourethral operation.

References
1. Eble JN, Young RH. Stromal osseous metaplasia in carcinoma of the bladder. J Urol. 1991;145:823-825.
[1] Yamaguchi K, Kitagawa N, Kotake T, et. al. Primary localized amyloidosis of the ureter associated with osseous metaplasia. Urol Int. 1991;47:164-166.
[2] Dudley AG, Tomaszewski JJ, Hughes AH, et. al. Incidentally Discovered Osseous Metaplasia Within High-grade Urothelial Carcinoma of the Bladder. Urology. 2011 (in press).
[3] Hartman RJ, Helfand BT, Dalton DP. Clear cell renal cell carcinoma with osseous metaplasia: a case report. Can J Urol. 2011;18:5564-5567.
[4] Willis SF, Bariol SV, Tolley DA. Bone formation in the urinary tract: case report. J Endourol. 2005;19:878-879.
[5] Lainas T, Zorzovilis I, Petsas G, et. al. Osseous metaplasia: case report and review. Fertil Steril. 2004;82:1433-1435.

Figure 1
A Pelvic X ray radiography showed showed half-arc shaped high density
B Excretory and retrograde urethrogram showing the anterior urethra stricture and irregular calculus.

Figure 2
Gross specimen of urethral stenosis. A 2.0 by 0.5 by 0.5-cm hard-texture cylindrical mass mixed with urethral mucus and bone like structure.

Figure 3
Pathological section; Haematoxylin and eosin stains (×200) showed chronic inflammation of urethra submucosa and multiple focal deposition of calcium salts (*) and with osseous metaplasia cells(→).

Date added to bjui.org: 22/11/2012

DOI: 10.1002/BJUIw-2012-042-web

We report a case of a fat containing renal mass, which was suggestive of angiomyolipoma and percutaneous ablation was initially considered.

Authors: A.Pai, S. Kumar, N. Onwu, A. Jones, Royal Berkshire Hospital
Corresponding Author: A. Pai, Department of Urology, Royal Berkshire Hospital, Reading. E-mail: [email protected]

Abstract

We report a case of a fat containing renal mass, which was suggestive of angiomyolipoma and percutaneous ablation was initially considered. The presence of tiny calcifications made us reconsider our differential diagnosis; a robotic partial nephrectomy revealed a clear cell renal cell carcinoma.

Introduction

It is widely accepted that evidence of macroscopic fat within a renal mass on CT is suggestive of angiomyolipoma (1). We describe a case where a 5cm fat-containing renal tumour was consistent with an angiomyolipoma and percutaneous ablation was initially recommended. Tiny areas of intratumoral calcification made us reconsider our management. A robotic partial nephrectomy was carried out, which revealed a clear cell renal cell carcinoma with osseous metaplasia. Despite the current consensus that angiomyolipomas over 4cm should be considered for percutaneous ablation (2) , this case shows that when there is diagnostic uncertainty, surgical excision should be considered as first line management.

Case Report

53 year old mechanical engineer presented as a general surgical patient with left sided abdominal pain. He underwent an ultrasound scan, with the incidental finding of a well defined heterogeneous solid mass in the upper pole of the right kidney.

A contrast CT scan confirmed a 5cm solid mass arising from the upper pole of the right kidney, separate from the adrenal gland. The lesion contained multiple hypoattenuating foci suggestive of macroscopic fat and a small amount of intratumoral calcification was shown (Figure 1).

Figure 1 Axial (Figure 1a), coronal (Figure 1b) CT images with IV contrast enhancement, showing a right renal mass with multiple foci of fat. Intratumoral microcalcifications are present.

Figure 1b.

The images were highly suggestive of an angiomyolipoma (AML) and since the lesion was bigger than 4cm, percutaneous ablation was initially recommended. However, the presence of a tiny amount of calcification visible within the tumour raised the possibility of a renal cell carcinoma (RCC).

A robotic right partial nephrectomy was carried out. Pathological examination revealed solid architecture with areas of metaplastic bone and adipose tissue associated with haemorrhage and degenerative changes with the tumour (Figure 2).

Figure 2. Photomicrograph of surgical specimen (haematoxylin eosin stain; original magnification: x100). Clear cell renal cell carcinoma with foci of metaplastic bone and adipose tissue.

The features were consistent with a clear cell renal cell carcinoma, Fuhrman Grade 3, with clear resection margins.

Discussion

Although it is clear that radiologically detectable fat is strongly associated with angiomyolipoma, there have been exceptions. In particular, there have been reports of fat-containing RCC’s (3-5). The engulfing of perinephric fat and cholesterol necrosis misinterpreted as macroscopic fat are the two most common mechanisms of fat deposition within RCC (4). The third, and rarest mechanism, is osseous metaplasia of the nonepithelial stromal portion of the tumour, with growth of fatty marrow elements and trabeculae (1,4). However this usually happens in cases of osseous metaplasia without calcification. Since this case contained calcification, this is unlikely to be the cause of the fat seen in this tumour.

In the reported cases of RCC with osseous metaplasia, the majority have shown some evidence of macroscopic calcification (3,5). In the present case, there was a tiny amount of calcification. Since AML only rarely shows evidence of calcification (4), it is clear that RCC should be considered in any fat-containing mass with calcification.

The advancement of percutaneous ablation for AML means it is imperative that the correct provisional diagnosis is made based on imaging. We suggest that in fat-containing lesions larger than 4 cm where there is uncertainty over the diagnosis of AML, diagnostic renal mass biopsy or surgical excision, should be considered as first line, invasive management.

References

1. Hélénon O, Merran S, Paraf F, Melki P, Correas JM, Chrétien Y, et al. Unusual fat-containing tumors of the kidney: a diagnostic dilemma. Radiographics. 1997 Feb;17(1):129-144.

2. Kothary N, Soulen MC, Clark TWI, Wein AJ, Shlansky-Goldberg RD, Crino PB, et al. Renal angiomyolipoma: long-term results after arterial embolization. J Vasc Interv Radiol. 2005 Jan;16(1):45-50.

3. Hélénon O, Chrétien Y, Paraf F, Melki P, Denys A, Moreau JF. Renal cell carcinoma containing fat: demonstration with CT. Radiology. 1993 Aug;188(2):429-430.

4. Richmond L, Atri M, Sherman C, Sharir S. Renal cell carcinoma containing macroscopic fat on CT mimics an angiomyolipoma due to bone metaplasia without macroscopic calcification. Br J Radiol. 2010 Aug;83(992):e179-181.

5. Roy C, Tuchmann C, Lindner V, Guth S, Vasilescu C, Saussine C, et al. Renal cell carcinoma with a fatty component mimicking angiomyolipoma on CT. Br J Radiol. 1998 Sep;71(849):977-979.

Date added to bjui.org: 02/11/2011

DOI: 10.1002/BJUIw-2011-066-web

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Osseous Metaplasia in Anterior Urethra

Fat-containing renal mass with small areas of calcification: surgical excision reveals renal cell carcinoma with osseous metaplasia

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