the physical examination revealed no specific findings except for the scar from the transplant operation . his serum creatinine on presentation was 1.7 mg / dl and urine analysis showed adequate red blood cells . there were no abnormal findings in the bladder during cystoscopy and he underwent an abdominopelvic computed tomography ( ct ) scan and retrograde pyelography , which revealed a 1.01.0 cm sized mass at the lower pole of the left renal pelvis ( fig . 1 ) . the abdominopelvic ct scan , as performed , did not reveal metastasis to other organs or lymph nodes but there was a left renal pelvis mass . the bone scan did not reveal bone metastasis , and the chest x - ray did not reveal any particular findings . a left nephroureterectomy with bladder cuff excision was performed and the pathological analysis showed a high - grade papillary transitional cell carcinoma ( tcc ) of the pelvis . six months later , a regular follow - up cystoscopy confirmed four tiny papillary masses on the left lateral wall . pathological tests showed a high - grade tcc , and the tmn staging was t1nomo ; mytomycin - c instillation therapy was performed . however , the bladder cancer recurred , and transurethral resection of the bladder tumor was performed six times in the next 5 years . an invasion into the bladder muscle layer was found , and the tnm staging was t2n0m0 . however , the patient refused additional surgery because of his anxiety over losing a functional organ . he came in for dialysis owing to decreased renal function . on the sixth month after the sixth transurethral resection of the bladder , a regular follow - up abdominopelvic ct revealed an enlarged lymph node near the right iliac vessel and multiple paraaortic and aortocaval lymphadenopathy with aggravated bladder wall thickening . in addition , the patient complained of left thigh pain ; thus , magnetic resonance imaging ( mri ) of the thigh was performed . the mri showed a 3.16.5 cm sized oval - shaped t1 slightly high and t2 heterogenous high - signal intensity lesion in the mid portion of the sartorius muscle ( fig . ultrasonography - guided biopsy of the nodular mass lesion in the left sartorius muscle was performed ( fig . the pathological analysis of the biopsy specimen revealed poorly differentiated metastatic urothelial carcinoma ( fig . 4 ) . chest ct and abdominopelvic ct showed lung , bone , and lymph node metastasis . radiation therapy to the left metastatic skeletal muscle lesion and chemotherapy to the metastatic bladder cancer were performed . although skeletal muscle represents approximately 50% of the total body mass and receives a large portion of total cardiac output , hematogenous metastatic disease to the skeletal muscle is extremely rare . several factors have been postulated to contribute to the resistance of skeletal muscle to metastatic disease . these factors include muscle motion and mechanical tumor destruction , inhospitable muscle ph , and the muscle 's ability to remove tumor - produced lactic acid that induces tumor neovascularity in other tissues . despite these defensive factors , metastases to skeletal muscle have been reported from pancreatic , renal , colonic , pulmonary , gastric , and ovarian primary malignancies . the malignant tumor to muscle metastasis per se isevidence of systemic spread , and metastatic disease to skeletal muscle tends to be found in people with advanced - stage neoplasms . the largest muscles , such as the erector spinae , psoas , and gluteals , are the most common sites of metastatic involvement . one large autopsy study of 5,298 people who died of malignancies found that 6% ( 298 ) involved the anterior chest wall or abdominal wall musculature and that 13% ( 666 ) involved the diaphragm . many of these lesions were microscopic and unlikely to be detected by any imaging technique . in this case , the patient complained of muscular pain , which is compatible with studies showing that most lesions are painful . skeletal muscle metastasis may be an incidental finding on ct of the chest or abdomen because most of the lesions identified were neither painful nor palpable . the general ct findings of skeletal muscle metastasis show an increase in ring - shaped enhancement with central hypoattenuation , and mri findings , although not specific , show low to intermediate signal intensity in the t1-weighted image and uniform high - signal intensity in the t2-weighted image . in this case , mri showed a 3.16.5 cm sized oval - shaped t1 slightly high and t2 heterogenous high - signal intensity lesion in the sartorius muscle and strong enhancement after contrast injection , which suggested intramuscular metastasis . reported that if painful muscle metastasis is present , en bloc excision has good effects . also , pop et al reported that although not statistically significant , there was a slight difference in survival rates among patients who underwent radiotherapy or chemotherapy compared with those who underwent different surgeries . however , klune et al .   reported that surgical treatment was selectively possible only in patients meeting various conditions and recommended radiotherapy or chemotherapy . regarding bladder tumor metastasis to skeletal muscle , nabi et al .   reported that the mean survival rate after receiving chemotherapy was 8 months , but because such cases are rare , specific details are not known . reported that in the case of lung cancer metastasis to skeletal muscle , the survival rate is considerably reduced compared with the absence of metastasis , and in the case of three patients , the survival rate was not good at 3 , 6 , and 30 months .