History: A 75-year-old man with a chronic history of microhematuria was referred for a CT urogram by his urologist.


Scout, coronal precontrast, axial nephrographic/excretory phase images, and volume-rendered coronal reconstructions of the left and right kidneys are shown below.










Additional history: The patient has a prior history of microhematuria and kidney stones. Review of the PACS for prior imaging reveals an intravenous pyelogram (IVP) from 2005. Scout and postcontrast exposures are shown below.




Findings  影像表现

CT urogram (2017): Noncontrast images demonstrate multiple bilateral nonobstructing renal calculi, the largest measuring 6 mm in the right kidney. Some of the calcifications could represent nephrocalcinosis — for example, those in the upper pole of the right kidney. The kidneys show symmetric enhancement without suspicious renal mass. Multiple bilateral exophytic simple renal cysts are noted, the largest in the midpole of the right kidney measuring 3.6 x 4.3 cm. There are additional subcentimeter low-attenuation lesions that are too small to characterize. There is a “paintbrush sign” appearance to the renal medullae in keeping with a history of medullary sponge kidney. There is mild bladder wall thickening and trabeculation that may be related to chronic outlet obstruction. Further evaluation is deferred to cystoscopy.

CTU:CT平扫可见双肾多发非梗阻性肾结石,右肾最大者直径约6mm,其中一些钙化可能代表肾结石,例如,右肾上极的那些。肾脏对称性强化,未见可疑肾肿物。双肾可见多发单纯性肾囊肿,大者位于右肾中部,大小约3.6 x 4.3 cm;另可见不足1cm的低密度灶,其太小而不能显示。肾髓质表现为“毛刷征”,符合髓质海绵肾。膀胱壁轻度增厚并小梁形成,与慢性流出道梗阻有关。进一步评估需膀胱镜检查。

IVP (2005): Preliminary scout images demonstrate a cluster of at least three radiopaque stones in the upper pole of the right kidney; the largest two stones in this cluster each measure 6 mm in diameter. In addition, there are probable clusters of smaller stones in the interpolar right kidney and right lower pole. Following the uneventful intravenous administration of 150 mL of nonionic contrast material, prompt nephrograms develop, which show the kidneys to be normal in size, shape, appearance, and internal architecture. There is diffuse bilateral tubular ectasia. Contrast is excreted promptly into otherwise normal-appearing pyelocalyceal systems. The calculi are no longer seen and likey reside in dilated tubules. The ureters are normal in course, caliber, and appearance. The urinary bladder has a mildly trabeculated appearance. There are two small urinary bladder diverticula: one of the bladder dome and one arising from the left lateral bladder wall. No filling defects are seen.


Differential diagnosis

  • Medullary sponge kidney
  • Nephrocalcinosis
  • Renal cortical necrosis
  • Renal papillary necrosis
  • Renal tuberculosis
  • Oxalosis
  • Renal pyramid “blush”: Normal homogeneous enhancement of pyramids with no tubular dilation


  • 髓质海绵肾
  • 肾结石
  • 肾皮质坏死
  • 肾乳头坏死
  • 肾结核
  • 草酸盐沉着症
  • 肾锥体充盈:肾锥体正常均匀强化,无肾小管扩张

Diagnosis: Medullary sponge kidney 


Key points

Medullary sponge kidney (MSK)


  • Medullary sponge kidney refers to a sporadic condition in which the medullary and papillary portions of the collecting ducts are dysplastic and dilated and, in most cases, develop medullary nephrocalcinosis. Occasionally, it can be hereditary.
  • Patients are predisposed for urinary stasis and resulting urolithiasis.
  • As many as 33% to 50% of patients have hypercalcemia (i.e., hyperparathyroidism).
  • The etiology and pathogenesis are unknown.
  • On cross section, the kidney appears as a sponge and there are multiple cystic cavities in the renal pyramids.
    • Cysts contain yellow-brown fluid and desquamated cells or calcified material.
    • Calculi within cysts and their walls consist of calcium oxalate ± calcium phosphate.
  • The size and number of renal calcifications typically increase with time.
  • The condition may be bilateral (75%) or unilateral (25%), and it may involve a single pyramid or segment.
  • The prognosis with MSK is generally good and patients will typically lead a normal life unless complications ensue. Complications include infection, extensive calculus formation, renal insufficiency, and renal failure.








可双侧(75%) 或单侧(25%),可累计单个或部分肾锥体;



  • The condition is more common in women.
  • The prevalence is estimated at 1 in 5,000 to 20,000.
  • Incidence at urography: 0.5%.
  • Incidence in patients with nephrolithiasis: 2% to 21%.



0.5%在尿路造影时偶然发现; 2%-21%在肾结石患者检查时偶然发现。

Clinical presentation

  • Most patients remain asymptomatic throughout their life, and the diagnosis is only made incidentally when the renal tract is imaged for other reasons.
  • However, approximately 10% of patients may present with a complication such as urinary tract infection, hematuria, or urolithiasis.




Imaging features  影像表现

Radiography: May see medullary nephrocalcinosis (calcifications within medulla) or urolithiasis.



  • Gross deformity of papillae with beaded or striated cavities
  • Distortion broad, shallow, or widely cupped calyces
  • Numerous large calcifications
  • May or may not have nephrolithiasis
  • More prominent linear densities
  • Clusters of small, rounded opacities in papillae (cystic dilatation of collecting ducts)
  • With or without enlarged papillae and splayed calyceal cups
  • “Bouquet of flowers” appearance: Ectatic collecting ducts filled with calcification
  • Large and dense medullary calcifications
  • “Paintbrush” appearance: More than three discrete linear densities in more than one papilla.
  • Collecting ducts wider than the normal 200-300 μm in diameter.
  • Mild/Moderate/Advanced ductal ectasia:
  • Evaluate the adjacent calyx for tumor (e.g., transitional cell carcinoma) or for obstructing calculi.


  • 肾盏严重畸形,可见珠状或条纹状囊腔
  • 扭曲、增宽、浅淡、扩张的杯状肾盏
  • 多发大钙化
  • 有或无肾结石
  • 较多明显线样影
  • 肾乳头内成簇的小圆形阴影(集合管囊状扩张)
  • 有或无扩大的肾乳头及八字形肾盏
  • “花束征”表现:扩张的集合系统充填钙化
  • 大而致密的肾髓质钙化
  • “毛刷征”表现:在一个肾乳头内超过三个分散的线样影
  • 集合管增宽,超过正常直径200-300 μm
  • 轻、中、重度肾小管扩张
  • 评估邻近肾盏有无肿瘤(如:移形细胞癌),或梗阻性结石

Retrograde pyelography:

  • No filling or poor filling of dilated collecting ducts is seen; contrast injection should not be forceful.
  • Tips of papillary ducts are not prone to reflux, regardless of disease severity.
  • Can help differentiate cysts of medullary sponge kidney from cysts of other medullary cavities (e.g., papillary necrosis or tuberculosis).


  • 可见未充盈或充盈较差的扩张的集合系统,造影剂注射无需用力;
  • 肾乳头肾小管尖部不易反流,与病变严重无关;
  • 有助于鉴别髓质海绵肾的囊肿与其它原因(例如:肾乳头坏死、肾结核)导致的髓质空腔而形成的囊肿。


  • Has a “paintbrush” appearance: Retention of contrast within dilated tubules in pyramids.
  • May or may not have medullary nephrocalcinosis and urolithiasis.
  • In severe disease, will see extracalyceal contrast accumulation within papillae or abscess.
  • May see hydronephrosis and hydroureter secondary to obstruction.


  • “毛刷征”表现:造影剂存留在肾盏的扩张肾小管内;
  • 有或无髓质肾钙质沉着及尿路结石;
  • 病变严重时,可见肾盏外造影剂积聚在肾乳头或脓肿内;
  • 尿路梗阻时可见肾积水、输尿管积水


  • MRI is an insensitive modality for detecting calcium.
  • Has decreased sensitivity in detecting tubular ectasia.


  • MRI对于钙化的检测不敏感;
  • 对肾小管扩张的敏感性减低。


There is no treatment for medullary sponge kidney. Treatment is based on managing complications when they arise, such as the following:

  • Antibiotics for infection
  • Thiazide and alkali therapy to decrease stone formation
  • Extracorporeal lithotripsy and percutaneous nephrolithotomy for stone removal


  • 抗生素治疗感染;
  • 利尿剂及碱性物质治疗降低结石形成;
  • 体外碎石及经皮肾结石切除术去除结石。












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