The patient is a 5-month-old Caucasian boy with no developmental abnormalities who presented Christmas Eve 2004 to his pediatrician with increasing fussiness, emesis, and inability to tolerate oral intake. He had a temperature of 100.2°F but otherwise normal vital signs. Physical exam at that time revealed a distended abdomen. He was sent home with a diagnosis of viral gastroenteritis.
Over the next 2 days, he continued to be fussy, developed diarrhea, and was not making wet diapers. He returned to the hospital December 27, 2004, and his exam was now significant for a palpable midline abdominal mass. A catheter was placed and drained 700 mL of urine. After draining the bladder, there was still a palpable abdominal mass slightly off midline to the left. The radiographic findings warranted surgical exploration.
A computed tomography (CT) scan of the abdomen and pelvis was obtained (Figure 1). This revealed a large retroperitoneal pelvic mass left of midline with calcified densities.
Dr. Jesse N. Mills: Dr. Harned, would you please comment on the radiographic findings in this case?
Dr. Roger K. Harned: In the setting of a clinically palpable mass, a CT scan of the pelvis was obtained. This was performed with administered intravenous and oral contrast material with limited non-contrast-enhanced images of the pelvis. The examination showed a 4.8-cm (craniocaudual) X 5.2cm (anteroposterior) X 4.6-cm (transverse) soft-tissue mass filling the lower pelvis, anterior to and inseparable from the sacrum with some protrusion into the left sacrosciatic notch. The bladder, containing a Foley catheter, was displaced anteriorly and superiorly by the mass. There was no bony erosion or expansion of the sacral foramina, and the sacrum was normally formed without cleft or segmentation anomaly.
The mass was of soft-tissue density, contained scattered punctate and linear calcifications, and enhanced homogenously after administration of intravenous contrast material. There were no associated fluid collections, and the mass contained no fat density material. The retroperitoneum was free of mass or adenopathy; adrenal glands were normal; and the liver enhanced homogeneously without evidence of metastatic disease.
Differential diagnosis based on the CT scan would include sacrococcygeal teratoma, rhabdomyosarcoma, neuroblastoma, and neurofibroma. The absence of associated bony abnormality and presence of scattered calcifications suggest neuroblastoma as the first choice. An I-123 metaiodobenzylguanidine (MIBG) scan was subsequently performed (Figure 2). The tumor demonstrated marked avidity for the radiopharmaceutical with no abnormal activity beyond the primary mass. This abnormal accumulation is specific for a tumor of adrenergic origin. Again, neuroblastoma is the most likely diagnosis, although a pelvic pheochromocytoma could also have this appearance.
Dr. Mills: Dr. Hendrickson, how did you plan your surgical approach and what are the technical considerations of this case?
Dr. Richard J. Hendrickson: My differential diagnosis prior to surgery was a neuroblastoma vs a sacrococcygeal teratoma, although one must favor a neuroblastoma based on the calcifications noted on CT scan. My plan was to perform a diagnostic laparoscopy with biopsy of the tumor. On the CT scan, I noted that the Foley balloon was anterior to this pelvic mass, which I thought would be amenable to a laparoscopic biopsy.
After the induction of anesthesia, a midline palpable mass was noted to extend from the symphysis pubis to the umbilicus. I was able to palpate the Foley balloon within this structure. Therefore, I decided to make a supraumbilical incision to avoid injury to the bladder. Also, on rectal exam, the mass was palpable. After placing my supraumbilical port (5 mm), two additional 5-mm ports were placed in the left and right abdominal wall. We noted a large cystic structure extending from the umbilicus down into the pelvis, presumably the bladder, although it looked abnormal and I thought possibly had calcifications in the wall.
During diagnostic laparoscopy, the pelvic tumor could not be safely identified. Dissection was performed down to the bifurcation of the internal and external iliac arteries. We clearly saw these vessels, as well as the ureters. Next, we instilled sterile water into the Foley and observed the midline cystic structure expand, confirming that this was indeed the bladder. It seemed odd to me that on CT scan the Foley balloon was juxtaposed to the pelvic tumor, and I could see the Foley balloon yet I could not identify the tumor. Again, the wall of the bladder appeared to have calcifications, and I wondered whether this was a bladder tumor rather than a pelvic/sacral tumor.
Therefore, I consulted Dr. Mingin for an intraoperative cystoscopy. Based on his findings, I aborted the laparoscopic approach, closed, and after further discussion with Oncology, Radiology, and Urology, decided to approach the tumor via a posterior sagittal approach with a coccygectomy the following day.
Dr. Mills: Dr. Mingin, you were consulted intraoperatively based on the fact that Dr. Hendrickson did not visualize the tumor laparoscopically. Please comment on the cystoscopic evaluation.
Dr. Gerald C. Mingin: First of all, this was a difficult cystoscopy secondary to the anterior displacement of the prostatic urethra and bladder neck by the tumor. Once I entered the bladder, I saw a pedunculated vascularized lesion emanating from the left lateral wall and dome of the bladder. I was able to use a resectoscope to take a deep biopsy of this lesion.
Dr. Mills: Dr. Lovell, please review the pathology for us.
Dr. Mark A. Lovell: The resectoscope biopsy contained urothelium and subjacent stroma but no recognizable tumor. A bone marrow aspirate was also negative for tumor. However, diagnostic tissue was obtained from the coccygectomy specimen. Figure 3 shows a small blue cell tumor infiltrating the soft tissue between the cartilaginous vertebrae without an appreciable Schwannian stromal component (Schwannian stroma-poor). At higher power (Figure 4), the neuropil background, in which scattered pseudorosettes are evident, confirms the diagnosis of neuroblastoma. Of note, no calcifications are seen in the sections examined. Electron microscopy performed as a subsequent quality assurance measure confirmed the presence of neurosecretory granules.
The International Neuroblastoma Pathology Classification[1,2] provides reproducible and clinically significant criteria to categorize neuroblastic tumors as having favorable or unfavorable histology. The first step is to determine if Schwannian stroma (the supporting component of nerves) is present in an appreciable amount. A tumor that is Schwannian stroma-poor (as in this case) is a neuroblastoma, as opposed to a ganglioneuroblastoma, which is stroma-rich.
Next, the tumor's degree of differentiation is assessed. This ranges from undifferentiated (meaning that the small blue cell tumor's neuroblastic character is only evident with immunohistochemical, ultrastructural, or cytogenetic studies) to poorly differentiated (the most common classification, as seen in this case), in which neuropil is evidence of neuroblastic differentiation, to differentiating tumors with at least 5% ganglion cells.
The next step is to assess the number of mitotic and karyorrhectic (apoptotic) cells to determine the mitotic-karyorrhectic index (MKI). The MKI may be low (< 100), medium (100-200) or high (> 200) relative to 5,000 cells, with high MKI always being unfavorable. In this case the MKI was low. Finally, the patient's age is factored in (generally younger or older than 18 months, but in the case of differentiating tumors with low MKI, the breakpoint is 5 years), with older age being unfavorable. Combining these four factors in this case categorizes the tumor as having a favorable histology.
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