Presentation
Screening US identified a complex right renal lesion, subsequent CT performed elsewhere confirmed it as a Bosniak 3 lesion. Referred for further evaluation.
Patient Data
- On B-mode US a heterogeneous cytsic right renal lesion is visible with a calcific focus and internal hypoechogenic content.
- MV-flow shows equivocal septal vascularity.
- During CEUS with SonoVue the cyst walls show avid enhancement, as well as a nodular septal thickening adjacent to the calcification.
- Findings altogether in line with a Bosniak 4 lesion.
- Small, about 20 mm inhomogeneously enhancing left kidney lesion already visualized in a previous CEUS exam (not shown).
MRI confirms the septal enhancement, of the complex cystic lesion, while also demonstrating the enhancing nodularity. About 18 mm solid, enhancing lesion in the left kidney, and multiple other smaller cysts with calcifications are also seen.
Preoperative staging CT:
- Known right renal cystic mass lesion without signs of local spread or distant metastases.
- Redemonstrated solid lesion of the left kidney, and smaller, about 10 mm cyst in the showing wall calcification.
- Other: hepatic cysts, status post cholecystectomy, small simple cysts in both kidneys, diverticulosis, enlarged prostate, atherosclerosis, degenerative changes of the depicted spine.
Case Discussion
Laparoscopic partial nephrectomy was performed. Postoperative histology did not confirm malignancy or cellular atypia. The internal content of the cyst was confirmed as fibrinous debris likely due to prior internal hemorrhage. Granulation tissue, metaplastic bone formation and red bone marrow were also found focally.
This cystic mass demonstrates that CEUS, multiphase CE-MRI, and CECT all have their limits in the characterization of complex renal lesions and it is always histopathology which has the final word. The avid enhancement caused by the internal granulation tissue and red bone marrow can hardly be expected, and from a radiological perspective this lesion was characterized properly. It has to be also noted that although exceedingly rare, extramedullary hemopoesis has been reported in cystic renal cell cancer too 1.
I would like to emphasize that biopsy of this lesion preoperatively would have been a mistake as due to internal tissue heterogeneity sampling does not provide results to be relied upon.
Subsequent follow-up so far showed no progression in the other complex cysts and the small left renal solid lesion, as of 2022 these have remained stable.
Altogether we have to once again remind ourselves that some rare tumor mimickers can evade preoperative diagnosis even using the most thorough imaging workup.
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