Olfactory groove schwannoma
Neurosurgery Department, University General Hospital of Alicante, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), Alicante, Spain
According to past reports, subfrontal schwannomas are occasionally described as olfactory schwannomas or olfactory groove schwannomas.
They are very rare tumors, leaving the issue of their origin controversial.
In 94 patients with anterior skull base (ASB) and sinonasal schwannomas, 44 (46.8%) were exclusively sinonasal, 30 cases (31.9%) were exclusively intracranial, 12 (12.8%) were primarily intracranial with extension into the paranasal sinuses, and 8 (8.5%) were primarily sinonasal with intracranial extension 1).
Li et al. gathered previous literatures and reported that results in 35 cases of olfactory schwannomas (between 1974 and 2010) has shown that 14 out of 30 cases (47%) (with the exclusion of five cases due to unknown olfactory function) had preserved olfactory function, but that the remaining 16 (53%) experienced either anosmia or hyposmia. Regarding the attachment sites of the schwannomas, they summarized that 12 cases were on the cribriform plate, 10 cases were on the olfactory groove, and 5 cases were on the skull base and skull base dura. When the tumor was attached to the cribriform plate, the rate of olfaction preservation was relatively high [9 of 11 cases (82%), excluding one case due to unknown olfactory function], compared to olfactory groove attachment [2 of 7 cases (29%), excluding three cases due to unknown olfactory function].
Figueiredo et al. systematically reviewed the literature concerning the anterior cranial fossa schwannomas to understand their pathogenesis, determine their origin, and standardize the terminology. They performed a MEDLINE, EMBASE, and Science Citation Index Expanded search of the literature; age, gender, clinical presentation, presence or absence of hyposmia, radiological features, and apparent origin were analyzed and tabulated. Cases in a context of neurofibromatosis and nasal schwannomas with intracranial extension were not included. Age varied between 14 and 63 years (mean = 30.9). There were 22 male and 11 female patients. The clinical presentation included seizures (n = 15), headache (n = 16), visual deficits (n = 7), cognitive disturbances (n = 3), and rhinorrhea (n = 1). Hyposmia was present in 14 cases, absent in 13 cases (39.3%), and unreported in five. Homogeneous and heterogeneous contrast enhancement was observed in 14 and 15 cases, respectively. The region of the olfactory groove was the probable site in 96.5%. Olfactory tract could be identified in 39.3%. The most probable origin is the meningeal branches of trigeminal nerve or anterior ethmoidal nerves. Thus, olfactory groove schwannoma would better describe its origin and pathogenesis and should be the term preferentially used to name it 2).
Because the olfactory and optic nerves lack a Schwann cell layer, these are not prone to develop into a schwannoma.
Some hypotheses about the genesis of olfactory groove schwannoma are centered on its developmental and non-developmental origins.
The developmental hypotheses suggest whether mesenchymal pial cells to transform into ectodermal Schwann cells or neural crest cells to migrate within the substance of the central nervous system .
The non-developmental hypotheses postulate that intracranial schwannomas arise from the Schwann cells normally presenting in the adjacent structures, such as the perivascular nerve plexus, the meningeal branches of the trigeminal and anterior ethmoidal nerves innervating the anterior cranial fossa and olfactory groove 3) 4).
Yasuda et al. 5) proposed the concept of an olfactory ensheathing cell (OEC) tumor in 2006. Olfactory ensheathing cells are glial cells that ensheath the axons of the first cranial nerve. Microscopically, both olfactory ensheathing cells and Schwann cells have similar morphological and immunohistochemical features. However, immunohistochemically olfactory ensheathing cells are negative for Leu7 and Schwann cells positive 6).
Often, these tumors can be confused for other entities, especially olfactory groove meningiomas and esthesioneuroblastomas.
With the recent advances in endoscopic skull base surgery, various anterior skull base tumors (ASB) can be resected successfully using an expanded endoscopic endonasal transcribriform approach through a “keyhole craniectomy” in the ventral skull base. This approach represents the most direct route to the anterior cranial base without any brain retraction. Tumor involving the paranasal sinuses, medial orbits, and cribriform plate can be readily resected. In a video atlas report, Liu and Eloy demonstrate their step-by-step techniques for resection of an ASB olfactory schwannoma using a purely endoscopic endonasal transcribriform approach. They describe and illustrate the operative nuances and surgical pearls to safely and efficiently perform the approach, tumor resection, and multilayered reconstruction of the cranial base defect. The video can be found here: http://youtu.be/NLtOGfKWC6U 9).
The prognosis after complete resection is known to be favorable 10).
When the tumor is attached to the cribriform plate, the preservation rate of olfactory function is higher compared to nearby structures 11).
Case reports after 2012
A case of a 49-year-old woman with an olfactory groove schwannoma attached to the cribriform plate without olfactory dysfunction. She had no specific neurological symptoms other than a headache, and resection of the tumor showed it to be a schwannoma. About 19 months after the operation, a follow-up MRI showed no evidence of tumor recurrence. Surgical resection through subfrontal approach could be one of the curative modality in managing an olfactory groove schwannoma. An olfactory groove schwannoma should be considered in the differential diagnosis of anterior skull base tumors 12).
Okamoto et al. report two cases of subfrontal schwannomas treated with surgical resection. In one case, the tumor was located between the endosteal and meningeal layers of the dura mater. This rare case suggests that subfrontal schwannomas may originate from the fila olfactoria 13).
A 24 year old lady presented with hemifacial paraesthesias. Radiology revealed a large olfactory region enhancing lesion. She was operated through a transbasal approach with olfactory preservation. 14).
One patient had intradural intracranial extension and required an extended endoscopic endonasal transcribriform approach with anterior skull base resection 15).
A 66-year-old woman presented with a 1-year history of progressive headaches. Clinical examination revealed hypoesthesia of the nasal tip. CT-scan and MRI studies revealed a large subfrontal tumor thought preoperatively to be a meningioma. Intraoperatively, a large extra-axial tumor arising from the floor of the right frontal fossa was encountered. Histopathology identified the tumor as a schwannoma. This current case gives strong clinical presumption of an origin from the anterior ethmoidal nerve. We reviewed the literature in order to establish the epidemiology of these tumors, from which there appear to be divergent profiles depending on tumor origin and histology. Despite close similarities with olfactory groove meningiomas, patient history and radiological findings provide substantial evidence for differential diagnosis 16).
Liu and Eloy demonstrate their step-by-step techniques for resection of an ASB olfactory schwannoma using a purely endoscopic endonasal transcribriform approach.
A case of schwannoma arising from the olfactory groove in a 16-year-old girl who presented with generalized seizures without olfactory dysfunction or other neurologic deficits. Computerized tomography (CT) scan showed a large mass with abundant calcification located in the olfactory groove, which was confirmed as a schwannoma by histology and totally resected via basal subfrontal approach.
The tumor was attached to the cribriform plate, and achieved gross total resection without compromising her olfactory function 17).