Metanephric adenoma is a kind of tumor that is rarely found in pediatric patients and has also been called a renal epithelial tumor, nephrogenic nephroma, and embryonal adenoma [1,2,3,4,5, 8]. Meanwhile, Fanconi–Bickel syndrome is a rare autosomal recessive disorder characterized by nonfunctional GLUT2 mutation, hepato-renal glycogen accumulation, both fasting hypoglycemia as well as postprandial hyperglycemia, and hypergalactosemia indicating an impaired utilization of these two monosaccharides, and proximal renal tubular dysfunction [6, 7]. The association between the two pathologies is extremely rare; hence reporting this case in pediatrics gave this report its scarcity.

The age range of patients presenting with MA varies widely from 15 months to 83 years [1, 4, 9]. Metanephric adenoma is reported to be more common in females, and tumors as small as 0.3 cm to as large as 15 cm have been described. In the context of MA, the developmental abnormality of other body systems has not been presented [1, 4]. However, association with other genetic syndromes is expected as MA was linked with some genetic mutations [10, 11].

FBS is an extremely rare disease, but with a distinct clinical entity. It usually presents below the age of 1 year with failure to thrive, severe hypophosphatemic rickets, and hepatomegaly [6, 7]. Proximal renal tubular dysfunction with glucosuria, phosphaturia, generalized aminoaciduria, bicarbonate wasting, and hypophosphatemia are characteristic findings [6, 7]. By two years of age, enlarged kidneys are noticed clinically. There have been no previous reports about any association with renal tumors. To our knowledge, this is the first case in the literature of a FBS infant with MA.

Our case was incidentally discovered, and most of the MA cases have no symptoms. Abdominal, flank pain, or hematuria could be other modes of presentation [1, 4, 5, 9]. Polycythemia and MA are frequently associated with 12% and 30% incidences in adults and children, respectively [1, 4, 8]. Yoshioka et al. in 2007 documented that MA can produce erythropoietin and hence cause polycythemia [12]. Our case of MA was associated with polycythemia and the blood picture was improved after surgical resection.

It is hard to discriminate between MA and other renal tumors at presentation [3]. Differential diagnosis includes Wilms’ tumor, other malignant tumors of the kidney such as clear cell sarcoma or rhabdoid tumors, or even renal cell carcinoma. Various imaging techniques cannot reliably differentiate between the benign from malignant nature of MA. There are certain imaging features that can help to suspect MA on renal ultrasound and CT scans [3, 4, 9, 11]. MA is usually hyperechoic and well-circumscribed on ultrasound and with lower attenuation than enhancing renal parenchyma on CT [4, 5, 8].

On a histopathological level, MA is composed exclusively of epithelial elements with tubular, glomeruloid, or papillary architecture, a virtual absence of mitoses and nucleoli, no vascular involvement, and negativity for cytokeratin 7 (CK7) and epithelial membrane antigen (EMA). The cells have rounded nuclei with scanty cytoplasm and low mitotic activity. These findings were consistent with our case in addition to the positive WT1 and CD57 staining [9, 10].

Surgical excision is the mainstay of management of MA because of its unknown malignant potentiality. Both radical and partial nephrectomies were reported either by open or laparoscopic approach [3,4,5, 11, 13, 14]. The decision depends mainly on the size and location of the tumor and its potential malignant nature. The renal function was reported to be stable or slightly decreased over time. Several reports supported the benefits of performing NSS for MA but most of these reports concerned adult patients and only a few cases were pediatric [3, 4, 13, 14].

In general, a solid renal mass found in a 21-month-old child is most likely to be a Wilms’ tumor. Based on the current guidelines, radical nephrectomy is the standard treatment, but recent data supported the efficacy of NSS in treating Wilms’ tumors even in those without tumor-associated syndromes such as Beckwith–Wiedemann syndrome and Denys–Drash syndrome [15,16,17]. In addition, renal dysfunction is predicted in the future due to the complication of FBS. For that reason, a NSS was performed in our case to preserve the functioning renal parenchyma.

After surgical resection of the tumor, no specific therapy is recommended. There have been reports of MA metastases, even though they are considered benign [2, 18]. Relapse and mortality did not occur in the reviewed literature on pediatric MA [3, 4]. There are no clear guidelines for the follow-up of such cases. Only a physical examination with imaging on a regular basis was recommended with no clear expectations regarding its outcome.

Finally, we think that the combination of MA and FBS in our case was a mere coincidence. To our knowledge, there was no reported association between FBS and childhood tumors except for one report of hepatocellular carcinoma [19]. GLUT gene family has a role in cancer metabolism and cancer targeted therapy and GLUT 2 has been expressed in some cancer cell lines indicating that it is involved in the cancer metabolism, not in carcinogenesis. Due to the rarity of the disease, we believe that there is no clear consensus for periodic screening of malignancies in patients with FBS.

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