The entire body is vulnerable to peripheral primitive neuroectodermal tumor invasion. The primary sites of pPNET are, indescending frequency, the chest wall, pelvis, retroperitoneum, abdomen, limb, and neck.10
In viscera, distinct cases of pPNET have been studied.3
However, in the English literature, only one case of pPNET of the mesentery was reported with perforation at presentation as was presented in our case study.4
pPNET prognosis is poor despite combined surgical, chemotherapeutic, and irradiation therapies. Only 25% of patients with tumors greater than 5 cm survive to 24 months according to Kushner et al.10
Histologically, Homer-Wright or Flexner-Wintersteiner rosettes and perivascular pseudorosettes may form from undifferentiated small round cells which constitute pPNET. Fibrosarcoma or malignant peripheral nerve sheath tumors, small cell undifferentiated carcinomas, and carcinoid tumors may resemble some areas within the lesions. It is known that tumors of neural crest origin can show bidirectional or multidirectional differentiation.7
Additionally, glial, ependymal, cartilaginous, and epithelial elements, though rare, have been found associated within pPNET.7
Hachitanda et al.11
reported a case of pPNET with epithelial and glial differentiation, and they suggested that the neoplastic neuroectodermal tissue can display a spectrum of differentiation. Although there has been no report of pPNET showing osteoid and bone production, it is thought that osteogenesis is a kind of differentiation of the tumor. Its prognostic implication is uncertain. Although several cases of bone and/or cartilage forming sarcomas have been reported in the literature,12
bone-forming pPNET has not.
Most authors agree that a useful tool in diagnosing pPNET immunohistochemically is CD99 (MIC2), which recognizes a 30/32 kDa surface glycoprotein.16
This marker is found in more than 90% of pPNET cases. Yet, many tumors, such as malignant lymphoma, leukemia, gastrointestinal stromal tumor, and small cell carcinoma, may demonstrate CD99 expression.17
Regarding pediatric malignant lymphoma and leukemia of T-cell lineage, Riopel et al.17
reported that CD99 expression was not uncommon.
The most objective diagnostic tool for pPNET is now considered to be karyotypic analysis for t(11;22)(q24;q12) translocation.2
This translocation occurs in more than 87% of the pPNET-Ewing's sarcoma cases. The detection of EWS/FLI-1
chimeric mRNA originating from the t(11;22)(q24;q12) translocation of the pPNET-Ewing's sarcoma family, facilitated by reverse transcription-polymerase chain reactions, have been reported in recent studies.2
Other small round cell tumors, including malignant lymphoma, leukemia (granulocytic sarcoma), rhabdomyosarcoma, leiomyosarcoma, gastrointestinal stromal tumor, desmoplastic small round cell tumor, malignant mesothelioma, undifferentiated carcinoma, small cell carcinoma, and conventional neuroblastoma offer a differential diagnosis of the current lesion being discussed. Through histological, histochemical, immunohistochemical and molecular methods, the lesion was meticulously examined to maintain distinction. Immunohistochemical staining with desmin, smooth muscle actin, CD34, cytokeratin, leukocyte common antigen, CD117, and CD99 were used to exclude the diagnosis of other small round cell tumors and gastrointestinal stromal tumors. In addition, chromosomal rearrangements involving the EWSR1 gene on chromosome 22q12 was detected by FISH, which was a strong supportive finding for pPNET. Most of the mass at the primary site was found in the mesentery of the jejunum. Direct invasion of the jejunal wall was also present, yet despite the large size of the tumor (12.0×8.0 cm), the degree of involvement of the mucosa of the jejunum was relatively limited. A final diagnosis of pPNET of the jejunal mesentery was applied to this tumor.
In conclusion, we have reported the first case of pPNET with osteoid and bone formation, arising from the mesentery of the small bowel with rupture at onset. The rupture was considered to be caused by local ischemic change, necrosis, and massive hemorrhage. Intraabdominal pPNET may present with acute abdomen and may reveal osteoid and bone formation, which leads to a high degree of importance for both surgeons and pathologists to consider.