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Page 4 of 15 Okafor et al. Mini-invasive Surg 2024;8:28 https://dx.doi.org/10.20517/2574-1225.2023.128

Doppler ultrasonography is a noninvasive, portable and relatively affordable imaging modality that offers
[35]
real-time visualization of cerebral vascularity without radiation exposure . Color Doppler ultrasonography
[36]
provides color mapping of cerebral vasculature and flow velocity . When paired with contrast agents, color
Doppler ultrasonography may help delineate blood flow of both large and small vessels feeding the tumor,
which may not be as easily discernible with traditional ultrasonography alone [36,37] . More recently, color
Doppler ultrasonography has been utilized intraoperatively in resection of various skull base pathologies
such as pituitary adenomas and meningiomas [37-39] . However, its use remains limited given operator-
[35]
dependent results .
Both CT and MRI provide essential information on the tumor’s relationship to adjacent bony landmarks
and soft tissue structures, respectively. Contrasted CT and MRI also help identify critical vascular structures
such as the intracranial portion of the internal carotid and its proximity to the lesion. However, these
conventional modalities may not fully capture the tumor’s vascularity as intricately as would CTA and
MRA. Both detail the cerebral vasculature with high-resolution images during specific arterial and venous
phases, which allows the surgeon to determine if pre-biopsy or preoperative embolization is warranted .
[40]
As both CTA and MRA offer equivalent results, the choice of CTA versus MRA depends on whether the
patient meets the criteria to undergo the respective study . Furthermore, if CTA or MRA indicates a high
[41]
risk of internal carotid artery (ICA) injury, then a balloon test occlusion (BTO) may be necessary to identify
collateral cerebral blood flow should the patient experience an ICA injury intraoperatively .
[40]
Lastly, fluorescence angiography can be employed as an adjunct intraoperative tool to help identify tumor
vascularity. Initially applied by neurovascular surgeons for use on patients with intracranial aneurysms or
intracranial dural fistula malformations, indocyanine green (ICG) has been used in endoscopic endonasal
surgery to assist with identification of vascular structures, nasoseptal flap (NSF) viability and tumor
identification [42-44] . ICG is administered intravenously and provides real-time identification of tumor
vascularity. Thus, its use is limited to intraoperative applications. Ultimately, utilizing the imaging
modalities in the setting of a patient’s coagulation history can help guide biopsy, thus allowing for both
biopsy and surgical resection planning.

Histologic assessment of well-differentiated specimens reveals a lobular architecture of small, round, blue
cells with uniform nuclei with salt-and-pepper chromatin and small or absent nucleoli [14,27] . In addition,
these well-differentiated masses are characterized by a typically low mitotic rate, high nucleus-to-cytoplasm
ratio and poorly defined cytoplasm [15,27,45] . Physical arrangements of these cells include Flexner-
[14]
Wintersteiner rosettes, glandular rings with a true lumen, or Homer-Write pseudorosettes . On the other
hand, poorly differentiated tumors exhibit a less defined architecture with increased pleomorphism, higher
mitotic rate, and necrosis, thus making it difficult to distinguish from other sinonasal masses. Inevitably,
immunohistochemistry (IHC) staining remains of the utmost importance as it narrows the differential
diagnosis and rules out other sinonasal tumors presenting in a similar fashion (i.e., Ewing’s sarcoma,
mucosal melanoma, rhabdomyosarcoma, sinonasal lymphoma, sinonasal undifferentiated carcinoma and
sinonasal neuroendocrine carcinoma) [14,15,27,45] . Notable positive markers include the expression of S100-
protein positive sustentacular cells and neuroendocrine markers such as neuron-specific enolase,
synaptophysin, and chromogranin. However, desmin, myogenin, vimentin, actin melanoma, myogenic and
Ewing sarcoma markers are negative . Ultimately, histology evaluation not only determines definitive
[46]
diagnosis but also establishes the foundation for pathologic grading.

Developed at the Armed Forces Institute of Pathology, the Hyams staging system [Table 1] was described in
1988 as a histologic grading system of olfactory neuroblastoma . This staging system categorizes the
[47]