Objective: Schwannomas of the anterior cranial fossa (ACF) are exceedingly rare, and their origin
remains controversial, with hypotheses suggesting various structures such as the ACF
base, olfactory nerve, and olfactory bulb. This debate extends to the classification
of olfactory ensheathing cell tumors, creating challenges in the nomenclature. Due
to their rarity and location, olfactory groove schwannomas (OGS) are frequently misdiagnosed
preoperatively as meningiomas, which are more common in this region. In this study,
we present the largest reported series of OGS cases, examining tumor origin, clinical
presentations, and surgical outcomes to provide insights into management strategies.
Methods: This retrospective analysis included all cases of olfactory nerve schwannoma treated
at our center from 1991 to 2023. We collected clinical and demographic data and reviewed
operative notes with radiological imaging using the hospital PACS system. Follow-up
data were also retrieved and analyzed for long-term outcomes. Additionally, a systematic
literature review was conducted using PubMed and Scopus to identify and compare previously
reported cases of OGS. Data from the literature were matched with our findings to
provide a broader understanding of these tumors.
Results: A total of 15 patients were identified with OGS. There were nine males and six females,
with a mean age of 33.5 years. All patients underwent surgical resection via a subfrontal
approach, (either a bifrontal or lateral subfrontal craniotomy). Gross total resection
(GTR) was achieved in 14 cases, as confirmed by postoperative MRI, while 1 patient
had a subtotal resection. No adjuvant therapy was administered. Postoperatively, five
patients experienced olfactory dysfunction, and two patients developed CSF rhinorrhea,
which was managed conservatively. One patient required reoperation due to tumor recurrence.
The mean follow-up was 9.3 years.
Our literature review identified 82 cases of OGS. The average patient age was 36.8
years, with a male-to-female ratio of 1.2. Headache was the most common presenting
symptom (68 cases, 82.9%), followed by preoperative anosmia (48 cases, 58.5%). On
imaging, the tumors were predominantly hyperintense on T2-weighted MRI and uniformly
showed contrast enhancement. Nasal or paranasal sinus involvement was observed in
28 cases (34.1%). GTR was achieved in 71 out of 77 cases with reported outcomes. Olfactory
dysfunction occurred in 31 patients (37.8%) postoperatively. CSF rhinorrhea was seen
in 9 patients, with 2 cases progressing to meningitis. Adjuvant radiotherapy was reported
in 2 cases, with 1 patient undergoing Gamma Knife radiosurgery and another receiving
conformal radiotherapy.
Conclusion: Schwannomas of the ACF base are rare, and patients often present with anosmia or
develop olfactory dysfunction following surgery. Approximately 30% of lesions exhibit
nasal or paranasal extension, heightening the risk of CSF rhinorrhea or meningitis
postoperatively. Although minimally invasive approaches such as endoscopic or supraorbital
craniotomies are viable options, GTR remains achievable in most cases with careful
planning. Long-term follow-up is essential for detecting early recurrence, where radiosurgery
may offer a feasible treatment option. Further research is needed to establish the
pathological origins of these tumors.
