Discussion
The finding of an abdominal mass in a child may be indicative of malignant disease, particularly in those under the age of five [1, 15]. Neuroblastoma is the most common abdominal malignancy in this age group, followed by WT; additional pediatric abdominal tumors include HB, non-Hodgkin’s lymphoma and germ cell tumors (GCT) [16]. Although radiological imaging can identify tumor location, neither US, CT nor magnetic resonance imaging is tissue specific [17]. Nevertheless, the SIOP-RTSG protocols recommend a clinical and radiological diagnosis of WT in children aged six months or greater, followed by preoperative chemotherapy [18]. Pathological diagnosis is only determined at the time of delayed nephrectomy, with pretreatment PCNB reserved for atypical cases [6, 19].
AFP can be a useful marker in cancer differential diagnosis, with more than 95% of HB and approximately 85% of NSGCT presenting high levels of AFP [20, 21]. The most prevalent malignant NSGCT in childhood are yolk sac tumors (YST), of which more than 90% show significant elevations in AFP [2, 22]. In contrast, only five cases of WT displaying raised AFP have been reported in literature [23, 24]. However, whilst the levels of AFP in both our patient (159.87 ng/mL) and those previously described were only mildly raised, in HB and YST they are often greater than 1000 ng/mL [25, 26]. Nonetheless, the increased AFP in our patient in addition to unclear tumor location on US examination, warranted the use of PCNB for early histologic diagnosis.
Despite there not existing a single marker or immunostaining panel that is diagnostic of WT, the Wilms tumor 1 (WT1) gene shows the greatest sensitivity and specificity, with positivity in more than 90% of cases [27]. Hence, the positive nuclear expression of WT1 in the biopsy of our patient helped confirm the diagnosis.
Around 10 to 15% of pleural effusions in the pediatric population result from malignancy, the third leading cause, yet they are rarely present in WT and are most commonly associated with lymphoma [27-29]. An abdominal mass that crosses the midline is also unusual in WT, occurring in only 20% of cases and was yet another uncommon finding in our patient [30]. Moreover, in spite of the eight kilogram unexplained weight loss experienced by our patient, constitutional symptoms such as fever, anorexia and cachexia are even less likely in WT, being reported in only 10% of cases [31].
To conclude, we describe a patient with WT in whom there was initial diagnostic uncertainty, with HB as the main differential diagnosis, due to elevated serum AFP and large tumor dimensions on