Leiomyoma of the renal capsule: case report and literature review

Introduction

Mesenchymal tumors are an exceptional finding in the urinary tract. Leiomyoma confined to the kidney are less than 100 in the literature and are a diagnostic challenge (1). Although most of these tumors are detected on autopsy, presentations as large and symptomatic masses have also been reported. A 4-5.5% prevalence based on autopsy findings has been reported. Two-thirds of all leiomyomas occur in women, with a greater prevalence in the Caucasian population (2, 3), being 65-70% of reported cases in this population. Although symptomatic cases are reported to be more common between the second and the fifth decades of life, incidental lesions are more commonly found in an older age group. We report a case of renal leiomyoma in a 47-year-old woman, who incidentally discovered a retroperitoneal mass with an abdominal ultrasound (US) scheduled for a conventional follow-up schedule of a mammary neoplasm.

Case description

A 47-year-old woman with no symptoms (no hematuria, no flank pain) presented at our institution for left renal tumor incidentally discovered during a follow-up US of abdomen executed for a history of mammary tumor. Abdominal US showed a solid mass located in the upper pole of the left kidney. Computed tomography (CT) confirmed these findings, showing a tumor in relation to upper pole of left kidney, measuring approximately 7 cm × 4 cm, with contrast uptake and no sign of adrenal infiltration. There was no vascular involvement or retroperitoneal adenopathies (Fig. 1).

OPEN IN VIEWER

Fig. 1

Coronal view of CT scan of left kidney leiomyoma.

Preoperative examinations were normal with no abnormality (blood tests, EKG, and chest x-ray negative for alterations and urine test was negative for microscopic hematuria).

On intraoperative examination, we report a well-circumscribed, greyish, and encapsulated round neoplasm with hard consistency. It appears to be originated by renal capsule and apparently separated from renal parenchyma. We also noticed increased vascularity of the perinephric fat tissue. For this reason, partial nephrectomy was carried out with an open flank surgical approach.

At microscopic examination, the tumor consisted of fascicles of long spindle cells organized in fascicles well-oriented, immerged in hyalinized stromal tissue. No mitosis, necrosis, or atypical cells were found. Immunohistochemical evaluation was positive for Vimentin, desmin, Caldesmone, smooth muscle actin, and negative for Melan-A, EMA, HMB45, CD34, S100 protein, AE1/AE3, and CD117. Ki-76 proliferation index was <1%. The diagnosis at final pathology was “leiomyoma of the renal capsule”.

Perioperative course was uneventful and the patient was discharged on fourth postoperative day. Four years after surgery, the patient is disease-free.

Discussion

Described for the first time in 1854 by Virchow, leiomyomas are rare, benign, mesenchymal tissue tumors originating from smooth muscle cells. In fact, as reported in literature, leiomyomas can originate from any organ of genitourinary tract that contain smooth muscle cells. So, we can find leiomyoma of renal capsule (most frequent), renal pelvis, cortical vessels, Dartos fascia, bladder, prostate gland, urethra, seminal vesicles, etc.

Renal leiomyomas account for 1.5% of benign lesions and 0.29% of all treated renal tumors, with autopsy evidence in 4.2-5.2% of cases (4). However, current reports of renal leiomyomas consist mostly of case reports and case series. Two-thirds of all leiomyomas occur in women. There also seems to be a greater prevalence in the Caucasian population, with approximately 65-70% of cases documented in that population (4).

Diagnosis of a leiomyoma by imaging is challenging. US may reveal a renal mass with its vascularization and margins but it lacks of specificity (5). CT scanning provides high definition images and reveals well-circumscribed margins, eventually a capsular origin, parenchymal alterations, and no evidence of extrarenal invasion (6).

However macroscopically, renal leiomyoma is a solid, well-circumscribed, encapsulated mass with a whorled surface (7). It is possible to find hemorrhagic areas and calcification. Histologically, the tumor shows intersecting fascicles of spindle cells with cigar-shaped nuclei and eosinophilic cytoplasm without significant pleomorphic nucleus or tumor necrosis.

Till today, surgery is the only therapeutic option and the prognosis is excellent without recurrence or risk of metastatic spread.

Conclusion

Renal leiomyomas are rare, benign, nonmetastasizing tumors with a good prognosis after surgical treatment. Till today, the differential diagnosis is still possible by histopathological examination and surgery is the only therapeutic option and the prognosis is excellent without recurrence or risk of metastatic spread.