Small round blue cell tumors of the sinonasal tract: a differential diagnosis approach

Abstract

One of the most challenging diagnostic categories within tumors of the sinonasal tract is the small round blue cell tumors. Biopsies are usually small and limited, resulting in considerable diagnostic difficulty for practicing surgical pathologists. These tumors share several overlapping histologic and immunophenotypic findings while also showing considerable variation within and between cases. Specific tumor site of origin, imaging findings, and clinical findings must be combined with the histology and pertinent ancillary studies if the correct diagnosis is to be reached. Discrimination between neoplasms is critical as there are significant differences in therapy and overall outcome. It is important to have a well developed differential diagnosis for this category of tumors, where each of the diagnoses is considered, evaluated, and either confirmed or excluded from further consideration. In an undifferentiated tumor, showing a small round blue cell morphology, using the mnemonic 'MR SLEEP' helps to highlight tumors to consider: melanoma, mesenchymal chondrosarcoma, rhabdomyosarcoma, sinonasal undifferentiated carcinoma, squamous cell carcinoma (including NUT carcinoma), small cell osteosarcoma, lymphoma, esthesioneuroblastoma (olfactory neuroblastoma), Ewing sarcoma/primitive neuroectodermal tumor, pituitary adenoma, and plasmacytoma. A panel of pertinent immunohistochemistry studies, histochemistries and/or molecular tests should aid in reaching a diagnosis, especially when taking the pattern and intensity of reactions into consideration.

Differentiation of olfactory neuroblastomas from nasal squamous cell carcinomas using MR diffusion kurtosis imaging and dynamic contrast‐enhanced MRI

“…Our preliminary results showed that DKI combined with quantitative DCE‐MRI are of great use in the discrimination of ONBs and SCCs, but they still need to be further verified by prospective, multicenter, large‐scale trials. Moreover, other rare tumors that occur in the superior nasal cavity, such as sinonasal undifferentiated carcinomas (SNUCs), sinonasal neuroendocrine carcinomas (SNECs), and the nuclear protein of the testis (NUT) carcinomas, should also be excluded when diagnosing the ONBs . SUNTs are rare malignant tumors with no squamous or glandular differentiation, which may mimic high‐grade ONBs .…”

“…Similar to SUNTs, SNECs can also occur anywhere in the sinonasal tract . SNECs are usually associated with higher aggressiveness, more frequent necrosis and lymphovascular invasion, as well as poorer prognosis than ONBs, which may contribute to the discrimination of these two entities . As for sinonasal NUT carcinomas, they are characterized by NUT gene rearrangement and abrupt squamous differentiation .…”

“…SNECs are usually associated with higher aggressiveness, more frequent necrosis and lymphovascular invasion, as well as poorer prognosis than ONBs, which may contribute to the discrimination of these two entities . As for sinonasal NUT carcinomas, they are characterized by NUT gene rearrangement and abrupt squamous differentiation . In comparison with ONBs, NUT carcinomas often present with more rapid growth, extensive destruction, and lymph node metastases, making it possible to differentiate them from ONBs .…”

Intraoperative squash cytology provides a qualitative intraoperative diagnosis for cases in which frozen section yields a diagnosis of equivocal brain tumour

“…Pathologists can often discern only whether the biopsy specimen contains tumourous tissue, while the origin of the tumour and tumour cell differentiation status remains unclear. Accordingly, they can provide only a tentative intraoperative diagnosis such as whether the specimen is of a tumour characterised by small round cells (small round cell tumour of uncertain origin) or by spindle‐shaped cells (spindle cell tumour of uncertain origin) . In such cases, equivocal brain tumour is diagnosed, and the tumour is later confirmed on analysis of the permanent sections to be, for example, a malignant lymphoma, glioblastoma multiforme, anaplastic oligodendroglioma, primitive neuroectodermal tumour or metastasis from another organ.…”

“…Accordingly, they can provide only a tentative intraoperative diagnosis such as whether the specimen is of a tumour characterised by small round cells (small round cell tumour of uncertain origin) or by spindle-shaped cells (spindle cell tumour of uncertain origin). [6][7][8][9] In such cases, equivocal brain tumour is diagnosed, and the tumour is later confirmed on analysis of the permanent sections to be, for example, a malignant lymphoma, glioblastoma multiforme, anaplastic oligodendroglioma, primitive neuroectodermal tumour or metastasis from another organ. An equivocal intraoperative diagnosis therefore leaves the neurosurgeon without sufficient information for how to proceed surgically.…”