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Page 2 of 13 Tang et al. Mini-invasive Surg 2024;8:24 https://dx.doi.org/10.20517/2574-1225.2024.04

INTRODUCTION
Skull base surgery began with the development of open approaches including transfacial approaches and
craniotomies to reach tumors in this anatomically-challenging area. These approaches continue to be used
and have a defined role in skull base surgery; however, the introduction of endoscopic skull base surgery has
provided skull base surgeons with greater access while reducing the invasiveness of procedures compared to
many open approaches. Now, with the advances in instrumentation, visualization, and surgical techniques,
endoscopic endonasal surgery (EES) is at the forefront of treatment for anterior midline skull base lesions.
This includes sinonasal malignant tumors (SNMT), which traditionally required open approaches and are
now amenable to purely EES, with the potential of providing less morbidity while maintaining comparable
[1]
oncologic outcomes . As instrumentation and surgeon technical experience continue to progress,
endoscopic endonasal techniques continue to expand providing a growing body of literature on EES for
[2]
various SNMTs . In many cases, EES provides the most direct approach to these tumors with maximal
visualization.

SNMTs represent a rare and heterogeneous disease group that presents with unique treatment challenges
based on disease characteristics and anatomical limitations . A retrospective analysis of the United States
[3]
National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) registry examined patients
diagnosed with SNMTs between 1973 and 2011 and found an incidence of 0.83 per 100,000 people with
squamous cell carcinoma (SCC) as the most common histology (41.9%) . Given the origin of SNMTs and
[4]
involvement of the sinonasal corridor, otolaryngologists naturally resected the majority of the sinonasal
portion of the tumor endonasally and increasingly endoscopically. However, neurosurgeons’ comfort with
transcranial approaches precluded initial extension of these approaches to the intracranial space. As a result,
SNMTs were traditionally approached via open techniques, alone or combined with endonasal exposure
and/or debulking. Despite this, a paradigm shift from en bloc tumor resection to piecemeal resection after
[5]
studies found that piecemeal resection provided equivalent outcomes has pushed EES to the forefront .
Nevertheless, SNMTs that extend into the skull base can be more challenging for resection through EES.
The role of EES in the multimodal treatment of SNMTs also varies depending on the biological behavior of
the tumor. This article reviews the current state of EES in surgical resection of SNMTs, describes the
advancements and outcomes of EES in SNMTs with skull base involvement, and provides pathology-
specific outcomes.

ANATOMICAL APPROACH AND CONSIDERATIONS PRIOR TO ENDOSCOPIC
ENDONASAL SURGERY FOR SINONASAL MALIGNANT TUMORS
The nasal cavity and sinuses serve as surgical corridors for endoscopic endonasal approaches involving the
skull base. Advantages of EES include improved visualization and decreased morbidity compared to
[6]
traditional approaches . However, a strong understanding of the endoscopic anatomy is paramount to
performing safe EES.

The ventral skull base lies inferior to the frontal lobes with the midline of the ventral skull base consisting of
the nasal cavity, ethmoid cells, and sphenoid sinus. The anterior two-thirds of the midline ventral skull base
are formed by the ethmoid bone. Critical structures in this area include the cribriform plate, fovea
ethmoidalis, and crista galli. The lateral lamella of the cribriform plate is a thin bony structure that connects
with the fovea ethmoidalis. The cribriform plate also contains the olfactory nerves and this space is an
important risk factor for skull base invasion from extracranial sinonasal tumors . Between the cribriform
[7]
plates, the crista galli joins the plates and serves as the attachment of skull base to the falx cerebri. During
EES, the anterior and inferior limits of the crista galli can serve as landmarks for the posterior table of the
frontal sinus. The ethmoid bone continues posterior to the cribriform plate portion and, at the midline, a