Indian Journal of Pathology and Microbiology

: 2023  |  Volume : 66  |  Issue : 1  |  Page : 180--183

Atrophic kidney-like lesion: A rare benign entity and mimicker of thyroid follicular-like carcinoma of kidney

Deepa Goel, Shilpi Modi 
 Department of Pathology, Artemis Hospitals, Sector - 34, Gurugram, Haryana, India

Correspondence Address:
Deepa Goel
Artemis Hospitals, Sector - 34, Gurugram, Haryana


Atrophic kidney like lesion (AKLL) is a recently described benign entity with only 14 cases reported so far. Genitourinary Pathology Society proposed inclusion of AKLL as a provisional entity in 2021. It mimics thyroid follicular-like carcinoma of kidney as it has a follicular architecture. We report a case of an 18-year-old female with detection of renal mass, while the patient was being investigated for abdominal pain. Mediastinal nodes were also enlarged with detection of necrotizing granulomas on biopsy. Histology revealed a tumor enveloped by a thick capsule with smooth muscle fibers, varying sized follicles, interspersed atrophic tubules, and calcifications. Immunohistochemically, the “cystic follicles” show WT1 +/PAX8 -/CK7-phenotype, while atrophic tubules present between “cystic follicles” harbor WT1 -/PAX8 +/CK7 + phenotype. Morphological diagnosis and differential diagnosis will be discussed.

How to cite this article:
Goel D, Modi S. Atrophic kidney-like lesion: A rare benign entity and mimicker of thyroid follicular-like carcinoma of kidney.Indian J Pathol Microbiol 2023;66:180-183

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Goel D, Modi S. Atrophic kidney-like lesion: A rare benign entity and mimicker of thyroid follicular-like carcinoma of kidney. Indian J Pathol Microbiol [serial online] 2023 [cited 2023 Mar 24 ];66:180-183
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Atrophic kidney like lesion (AKLL) is a recently described benign entity with only 14 cases reported so far.[1],[2] A few of them were initially reported as thyroid follicular-like carcinoma of kidney (TFLCK) and later reclassified as AKLL.[1] This tumor has a predilection for younger patients and has a benign clinical outcome. Initially, it was described as “distinctive renal cell tumor simulating atrophic kidney with two types of microcalcifications” by Hes et al.[3] in 2014 and classified as AKLL later. The lesion is characterized by the presence of thick capsule rich in smooth muscle and low-power appearance of follicular architecture. Immunohistochemically, the “cystic follicles” show WT1 +/PAX8 -/CK7- phenotype, while atrophic tubules present between “cystic follicles” harbor WT1 -/PAX8 +/CK7 + phenotype.[1] Etiopathogenesis of this lesion is still not known. There is a single case report where patient had coexistence of bladder cancer.[2] We report a case of an 18-year-old female with detection of renal mass, while the patient was being investigated for abdominal pain. The patient was found to have mediastinal nodes as well, which on histopathology revealed necrotizing granulomas.


An 18-year-old female presented with right flank pain. There was no complaint of hematuria, fever, or cough. Her complete blood count and renal function tests were within normal limits. Contrast enhanced computed tomography whole abdomen revealed well-defined heterogeneously enhancing lesion arising from the upper pole of the right kidney measuring approximately 8.6 × 7.5 × 2 cm. No evidence of renal vein or inferior vena cava invasion seen. Mediastinal nodes were also enlarged. Ovaries were normal in size and echotexture. Clinical diagnosis of renal cell carcinoma (RCC) with metastases to mediastinal nodes was made. Mediastinoscopic biopsy of mediastinal nodes was taken. Right nephrectomy was performed. Grossly, nephrectomy specimen measures 10 × 5.5 × 3.5 cm. The surface shows a partially exophytic, encapsulated mass lesion measuring 8.6 × 7.5 × 2.0 cm. The cut surface is brownish in color with tiny cystic spaces [Figure 1]a.{Figure 1}

Microscopic examination of mediastinal nodes revealed necrotizing granulomatous lymphadenitis. No fungal organisms were seen. Although Zeil Neelson stain did not reveal any acid fast bacilli, morphologically granulomas were consistent with tuberculosis.

Microscopic examination of kidney showed a tumor enveloped by a thick capsule with smooth muscle fibers [Figure 1]b. Entrapped blood vessels and tubules were seen. Lesion was composed of variable sized cystic spaces resembling thyroid follicles. These contain deeply eosinophilic colloid-like material, which show retraction from the epithelial lining cells. Follicular cystic spaces forming the predominant component of tumor were lined by the single layer of flattened to atrophic epithelial cells with small-sized, normochromatic nuclei [Figure 1]c. At places, hobnailing was noted. No nuclear grooving or pseudoinclusions seen. Some discohesive rounded cells were appreciated within the follicular cysts. Intervening stroma is hyalinized and contains two types of atrophic tubular structures –1) endocrine type having narrow lumina and clear cytoplasm and 2) thyroidization type [Figure 1]d. At places, some bundles of smooth muscles were noted in the tumor stroma. No mitotic activity or pleomorphism was seen. The follicular cystic spaces were surrounded by rich capillary vascular network. Some thick walled vessels also seen. Two types of calcifications were seen, dystrophic and psammomatous, within the cysts and cyst wall [Figure 1]e. No areas with clear cells seen. There was no sarcomatoid differentiation/rhabdoid element/necrosis seen. No lymphovascular emboli seen. Renal vascular and ureter margins were free of tumor. Lymph nodes were not submitted for evaluation. Native kidney was unremarkable.

Differential diagnosis of AKLL, primary TFLCK, thyroidization of tubules, metastases from follicular carcinoma originating from thyroid, or struma ovarii was kept. Immunohistochemistry revealed follicular cystic spaces to be diffusely positive for panCK [Figure 2]a, Vimentin [Figure 2]b, CD10 [Figure 2]c, and negative for PAX8 [Figure 2]d. In contrast, atrophic tubules showed PAX 8, CK7 [Figure 3]a, and CK19 [Figure 3]b positivity. Follicular cystic spaces were positive for WT1 [Figure 3]c. WT1 reactivity was also noted in intraluminal discohesive cells. TTF1 [Figure 3]d was negative throughout. SMA highlighted smooth muscle bundles, within the capsule [Figure 3]e. CD34 stain highlighted rich vascular network around the follicular cystic spaces [Figure 3]f. Diagnosis of AKLL was given. Tumor stage was pT2a, and ISUP/WHO nuclear grade was G1.{Figure 2}{Figure 3}


TLFCK is a provisional entity in the 2016 WHO classification of kidney tumor with less than 40 cases reported in world medical literature.[4],[5] Genitourinary Pathology Society proposed inclusion of AKLL, as provisional entity in 2021.[6] Herlitz et al.[1] published largest clinicopathologic series of eight cases of AKLL and described the morphological and immunohistochemical features of AKLL distinct from TLFCK. According to their criteria, it can be distinguished morphologically from AKLL by the absence of atrophic tubules in between cystic follicles, which are CK7, CK19, and PAX 8 positive. There is back-to-back arrangement of follicles in TLFCK, which are WT1 negative. In AKLL, the cystic follicles are WT1 positive, which is consistent with podocyte and parietal epithelial cell lineage. Also, smooth muscle-rich capsule is not described in TLFCK. The cells lining the cystic follicles show more cytoplasm, nuclear irregularity, and may show complex branching architecture in TLFCK. It is important to distinguish between these two entities as clinical course in AKLL cases reported so far have been indolent. In contrast, a few cases of TLFCK had shown metastases to retroperitoneal nodes, lung, skull, and meninges.[7],[8]

End stage renal disease is a benign process with thyroidization of tubules; hence, no mass formation noted. Moreover, it is a diffuse process. The interspersed atrophic tubules of endocrine type are due to ischemia, while thyroidization type tubules are attributed to slow intratubular flow. Herlitz et al.[1] studied 10 cases of non-mass-forming glomerulocystic disease as a control group and found remarkable histologic and immunohistochemical similarity to AKLL. The native kidney was normal in all the cases described so far, including ours.

Metastasis from thyroid carcinoma/struma ovarii is even rarer phenomenon and show TTF-1 positivity. WT1 reactivity in lining cells and intraluminal discohesive cells suggests that cystic follicle-like structures are cystic glomeruli in origin and not derived from tubules. There are other renal tumors that can show follicular-like architecture, namely, papillary RCC, succinate dehydrogenase-deficient RCC, microcystic chromophobe RCC, and rarely MiT family translocation RCC. However, these changes are focal and classical areas of that tumor entity are seen predominantly.[4] One should exclude all these entities before diagnosing AKLL. Metanephric adenoma show tightly packed small tubules with papillary tufts and glomeruloid structures. Cystic change, dystrophic, and psammomatous calcifications can also occur. However, these do not have a thick capsule as seen in our case. Tubulocystic renal carcinoma of kidney is composed of empty cystic spaces separated by fibrous septa of varying thickness. These usually have high nuclear grade and Pa × 8 positivity. Renal angiomyoadenomatous tumor, now known as RCC with (angio) leiomyomatous stroma, also shows a leiomyomatous capsule with prominent vascular and smooth muscle stroma. These are composed of branching tubules/papillary tufts with clear cells and show positivity for CK7.[4] No clear cells were seen in our case.

The tumor size reported so far ranged from 1.6 to 6.5 cm and have been staged as pT1; however, in our case, it is 8.6 cm and staged as pT2a. She took antitubercular treatment for 9 months. After 4 years of close follow-up, there is no evidence of disease recurrence. This patient had morphological evidence of tuberculosis in mediastinal nodes. No such associations have been reported so far. One case associated with urothelial carcinoma of bladder has been reported.[2] Whether these are coincidental findings or has some role in etiopathogenesis is not certain. Oshiro et al. reported a case with bilateral AKLL.[9] More clonality studies are needed to ascertain the nature of this lesion whether reactive or neoplastic.

To conclude, AKLL is a rare benign entity with excellent prognosis, which occurs in younger age group, characterized histologically by an encapsulated mass of varying sized follicles, interspersed atrophic tubules, and calcifications.

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