Giant adult multilocular cystic nephroma weighing 16 kg: a case report

¹Department of Urology, Cheikh Khalifa International University Hospital, Mohammed VI University of Sciences and Health (UM6SS), Casablanca, Morocco, ²Department of Pathology, Cheikh Khalifa International University Hospital, Mohammed VI University of Sciences and Health (UM6SS), Casablanca, Morocco

^&Corresponding author
Omar Iraqui Houssaini, Department of Urology, Cheikh Khalifa International University Hospital, Mohammed VI University of Health Sciences (UM6SS), Casablanca, Morocco

Introduction    

Multilocular cystic nephroma (MCN) is a rare, benign, slow-growing renal tumor of unclear origin, first described by Edmunds in 1892 [1] and classified, according to the WHO classification of urinary tumors, within the spectrum of mixed epithelial and stromal tumors of the kidney [2,3]. Its clinical and radiological presentation is nonspecific and frequently overlaps with cystic renal cell carcinoma, making preoperative diagnosis difficult; only histopathological examination can confirm the diagnosis with certainty and rule out cystic or necrotic pseudocystic renal carcinoma. The literature reports fewer than 200 cases to date, and the largest MCN previously described weighed 5.5 kg. We report a case of MCN weighing 16 kg in a 23-year-old woman, an age markedly below the usual adult peak (fifth to sixth decade), which, to our knowledge, is the largest MCN reported to date, far exceeding the previous record. This case is unique in combining an unusually young age of onset with an exceptional tumor volume, and it adds to the literature by showing that this rare benign entity can reach dimensions not previously reported, while still posing the same diagnostic and surgical challenges as smaller lesions.

Patient and observation     

Patient information: a 23-year-old female patient, with no known medical, surgical, or toxic history, presented following the onset of abdominal pain evolving over several months, associated with bloating and a sensation of abdominal heaviness. The course was subsequently marked by the onset of diffuse bilateral low back pain, prompting her to seek consultation. No known personal, family, or psychosocial history was reported, and no relevant genetic information was identified. The patient had no prior interventions related to this condition.

Timeline: several months before admission, the patient developed progressive chronic abdominal pain, bloating, and abdominal heaviness. Weeks before admission, she developed diffuse bilateral low back pain, prompting consultation. On the day of admission, clinical examination revealed a large abdomino-pelvic mass, and abdomino-pelvic MRI and laboratory work-up were performed. On day 0, a left total nephrectomy was performed for combined diagnostic and therapeutic purposes. From day 0 to day X, the patient was monitored in the intensive care unit without complications before transfer to a conventional ward, with preventive anticoagulation and antibiotic therapy initiated. The drain was removed and the patient mobilized on day 5, and she was discharged in satisfactory general condition on day 6. Postoperatively, histopathological examination confirmed a benign multilocular cystic nephroma with clear margins, and clinical and radiological follow-up was planned.

Clinical findings: on clinical examination, the patient was hemodynamically and respiratorily stable, well oriented in time and space. Inspection revealed a large, ovoid, poorly defined abdomino-pelvic mass, firm and smooth in consistency, tender on palpation, and immobile with respiratory movements.

Diagnostic assessment: given the clinical findings, an abdomino-pelvic MRI was performed, revealing a large left renal mass measuring 321 mm (transverse) × 254 mm (anteroposterior) × 332 mm (height), heterogeneous, with iso- to hyposignal on T1 and heterogeneous hypersignal on T2. It showed large necrotic or cystic intratumoral areas, peripheral tumor enhancement after contrast injection, and diffusion restriction (Figure 1). The left kidney appeared flattened and almost entirely effaced, with dilation of the pyelocaliceal system. The mass crossed the midline, displacing the pancreas, stomach, liver, left colon, and contralateral colon, without signs of direct infiltration (Figure 1). The left renal artery and vein remained patent, without thrombus or vascular invasion. There was no retroperitoneal lymphadenopathy, effusion, or visible secondary lesion. The preoperative differential diagnosis mainly included cystic renal cell carcinoma, a mixed epithelial and stromal tumor, or, more rarely, cystic nephroblastomatosis, given the size and heterogeneity of the mass. Additional laboratory tests were also unremarkable; the complete blood count showed hemoglobin at 12.4 g/dL, no leukocytosis, and a platelet count of 289,000. On the ionogram, the patient had no electrolyte disturbances, and renal function was preserved, with urea at 0.21 g/L and creatinine at 5.10 mg/L. Urine culture was sterile. The remainder of the laboratory workup was unremarkable. As imaging and laboratory findings could not formally exclude a malignant lesion, and given the persistent diagnostic uncertainty, the decision was made to proceed with surgical excision for both diagnostic and therapeutic purposes, as no radiological or biological criterion could reliably rule out malignancy prior to surgery.

Therapeutic intervention: a left total nephrectomy was performed for combined diagnostic and therapeutic purposes (Figure 2).

Follow-up and outcome: the immediate postoperative course required monitoring in the intensive care unit, without complications, before transfer to a conventional hospital ward. Preventive anticoagulation and postoperative antibiotic therapy were initiated. The drain was removed on day 5, with the patient mobilized the same day. She was discharged on day 6 in satisfactory general condition. Macroscopic examination revealed a renal mass weighing 16 kg and measuring 35 × 22 cm, with a multilocular cystic appearance on cut section and thickened whitish septa. The renal capsule appeared intact, with a 2 cm residual rim of renal parenchyma. The resection margins were inked, with no suspicious nodular area identified macroscopically (Figure 3). Microscopic examination likewise showed a well-circumscribed tumor formation, composed of a network of cystic cavities of variable size separated by thick fibrous septa, lined by a single layer of cuboidal or flattened epithelium, focally columnar with eosinophilic cytoplasm, with a discrete "hobnail" appearance in places, without cytonuclear atypia, mitotic figures, or necrosis. The septa consisted of thick fibrous connective tissue with a mild inflammatory infiltrate, without a blastemal or primitive mesenchymal component. The adjacent renal parenchyma showed preserved morphology, and the surgical, vascular, and ureteral margins were free of tumor. The pathological conclusion favored a diagnosis of adult multilocular cystic nephroma, with clear surgical margins and no histological evidence of malignancy.

Patient perspective: the patient reported experiencing apprehension before the surgical procedure. She describes marked relief in the postoperative period, with overall satisfaction regarding her care.

Informed consent: written informed consent was obtained from the patient for publication of this case and the associated clinical and imaging data.

Discussion     

Multilocular cystic nephroma (MCN) is a rare benign cystic renal tumor, first described by Edmunds in 1892 under the term cystic cystadenoma [1]. It is now classified, according to the World Health Organization (WHO) classification, within the spectrum of mixed epithelial and stromal tumors of the kidney [2,3]. Although cystic tumors account for approximately 10% of renal tumors, MCN remains exceptional, with just over 200 cases reported in the literature [2,4]. Multilocular cystic nephroma (MCN) shows a characteristic bimodal distribution, affecting young children on one hand, and middle-aged adults, with a marked female predominance between the fifth and sixth decades, on the other [4]. The pathophysiology of MCN remains debated, historically oscillating between the hypothesis of a developmental malformation and that of a true neoplasm [3]. Our case concerns a 23-year-old patient, an age markedly younger than the peak usually described in adults. This unusual presentation is one of the main distinctive features of this case and underscores that this diagnosis should also be considered in young subjects presenting with a large cystic renal mass. Most cases are asymptomatic and discovered incidentally on radiological workup. Typical clinical manifestations include a mass syndrome, associating lumbar or abdominal pain, hematuria, a palpable mass, or urinary tract infections, occurring at any age [4]. Our patient presented with similar symptoms, dominated by chronic abdominal pain with a sensation of heaviness, subsequently complicated by bilateral low back pain. There were no signs of hematuria, hypertension, or recurrent urinary tract infections. However, the presence of a large palpable abdomino-pelvic mass reflects a much more advanced course than that usually reported in the literature.

Imaging and tumor size: imaging plays an essential role in the preoperative workup but remains insufficient to establish a definitive diagnosis. CT typically shows a multilocular mass with thin, contrast-enhancing septa, sometimes associated with calcifications, most often corresponding to a Bosniak III or IV lesion [5,6]. However, as highlighted by Levy et al. no radiological criterion is sufficiently specific to formally distinguish MCN from cystic renal cell carcinoma or another complex cystic tumor [5]. MRI can provide complementary information, particularly by analyzing the fluid content, septa, and any solid areas, without fully resolving diagnostic uncertainty. Our case is distinguished above all by the exceptional volume of the tumor. Magnetic Resonance Imaging(MRI) showed a mass measuring approximately 32 × 25 × 33 cm, almost completely flattening the left kidney, crossing the midline, and displacing neighboring organs without signs of invasion. These dimensions far exceed those of the largest published series, in which lesions rarely exceed 10 to 12 cm [4]. The left kidney appeared flattened and almost completely effaced, with crossing of the midline and displacement of neighboring organs without signs of infiltration — a presentation which, in its extensive nature, more closely resembles the rare reports of large tumors with extension to the renal pelvis or retroperitoneum mentioned as exceptional in the literature. Magnetic Resonance Imaging(MRI), whose specific diagnostic contribution is considered limited in the literature for cystic nephroma but useful when there is doubt regarding cystic cancer, showed in our case peripheral enhancement and diffusion restriction [5]. These elements, combined with the size and heterogeneity of the mass, maintained preoperative diagnostic uncertainty, consistent with the classic difficulty in distinguishing this benign tumor from a necrotic cystic renal cell carcinoma or another mixed epithelial and stromal tumor.

Surgical management: it should be noted that preoperative imaging and macroscopic examination cannot fully differentiate a malignant tumor; therefore, surgical treatment with histological analysis remains the reference method for diagnostic confirmation [5,7,8]. When the lesion is small (< 4 cm), unilateral, well defined, and technically accessible, conservative surgery should be favored to preserve nephron mass, combined with intraoperative frozen-section examination (7,8). Conversely, total nephrectomy remains indicated when tumor size, destruction of the renal parenchyma, or suspicion of malignancy make partial excision unfeasible or oncologically uncertain [7,8]. Given the persistent diagnostic uncertainty despite imaging, the exceptional size of the mass, and the absence of any formal argument excluding malignancy, a left total nephrectomy was performed for both diagnostic and therapeutic purposes in our case.

Pathology: the definitive diagnosis therefore relied exclusively on histopathological examination. Macroscopic examination of the surgical specimen, particularly striking in our case (16 kg, 35 × 22 cm), revealed a well-circumscribed mass. Examination showed a multilocular cystic appearance with thickened whitish septa and a residual rim of renal parenchyma, an architecture comparable to that described in the literature [4,9]. Microscopically, our case showed the full set of classic histological criteria for multilocular cystic nephroma: cystic cavities lined by a single layer of cuboidal or flattened epithelium with a focal hobnail appearance, absence of cytonuclear atypia, absence of mitoses and necrosis, fibrous septa without a blastemal or primitive mesenchymal component, and adjacent renal parenchyma of preserved morphology [2,3,9]. These findings correspond precisely to the eight diagnostic criteria proposed by Powell and Boggs: unilaterality, solitary nature, multilocular lesion, absence of communication between the cysts and with the renal pelvis, flattened epithelium, absence of nephrogenic tissue in the septa, normal residual parenchyma, and confirm, as recalled in the literature, that only histopathological examination can establish this diagnosis with certainty [9,10]. There is another method of differential diagnosis involving testing for the DICER1 gene mutation, an alteration present in anaplastic sarcoma of the kidney, which can arise in renal areas where a cystic nephroma was pre-existing. This testing is not systematic and is difficult to access within our public health system; for this reason, it was not performed in our case.

Outcome: in general, nephrectomy is the treatment of choice, as it allows both a definitive diagnosis and definitive treatment [3]. The prognosis of MCN is excellent after complete excision. Our patient's postoperative course was uneventful, with discharge on day 6. Recurrences remain exceptional and are mainly described after incomplete resection. Although malignant transformation is exceptional, clinical and radiological follow-up is recommended to detect any local recurrence [2,3,7].

Strengths and limitations: the main strength of this report lies in its complete clinical, radiological, and histopathological documentation of the largest MCN reported to date, which extends the known upper limit of tumor volume for this entity and highlights that it can occur well below the usual adult age peak. As with any single case report, the main limitation is the inherent lack of generalizability of an isolated observation. Molecular testing for the DICER1 mutation, which could have helped exclude anaplastic sarcoma of the kidney arising within a pre-existing cystic nephroma, was not accessible in our setting and was therefore not performed, which constitutes a further limitation of the diagnostic work-up. Finally, follow-up remains short at the time of writing, and longer radiological surveillance will be needed to confirm the durability of the favorable outcome

Conclusion     

This case illustrates a particularly unusual presentation of multilocular cystic nephroma, combining an early age of onset with an exceptional tumor volume. It highlights that, despite advances in imaging, preoperative diagnosis remains difficult and that only histopathological study can establish a definitive diagnosis. Finally, it underscores that surgical strategy must be individualized according to the characteristics of the lesion, favoring conservative surgery whenever possible, while reserving total nephrectomy for large forms or when malignancy cannot be reasonably excluded.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Omar Iraqui Houssaini: investigation, data curation, visualization, writing - original draft. Younes Houry, Moussaab Rachid, Ghassane El Omri, Fekkak Hamza, Tahar Tazi, Najat Lamalmi: investigation. Abdeljalil Heddat: conceptualization, supervision, validation, writing - review and editing. All authors read and approved the final manuscript.

Figures     

Figure 1: contrast-enhanced abdominal CT, axial (A) and coronal (B) sections: large multilocular cystic mass of the left kidney, with thin enhancing septa (arrows), without tissue component or fleshy nodule, consistent with cystic nephroma

Figure 2: macroscopic appearance of the left nephrectomy specimen

Figure 3: (A,B,C,D) histological image showing cystic cavities of variable size lined by a single layer of regular columnar cells without cytonuclear atypia

References