The puzzling olfactory groove schwannoma: a systematic review

Olfactory Groove Schwannoma or Olfactory Ensheathing cell Tumor?

BACKGROUND

Schwannomas are benign tumors that arise from Schwann cells. Rare cases are shown to arise from the olfactory nerve. The genesis of Olfactory groove schwannoma (OGSs) is still puzzling. Yusda et al hypothesized that olfactory ensheathing cell tumors (OECTs) might be the origin of OGSs.

CLINICAL PRESENTATION

Here, the authors report the case of a 59-year-old woman who presented with a paroxysmal headache for 1 year. The tumor appeared as hypointensity on T1-weighted images, hyperintensity on T2-weighted, and exhibited strong, heterogeneous enhancement. The tumor was removed through a lateral supraorbital approach. The final pathologic diagnosis was schwannoma. The postoperative period was uneventful after 4 months, and the headache disappeared.

DISSCUSSION AND CONCLUSION

OGSs and OECTs are extremely rare. There are many similarities in clinical manifestations, images, and pathologic findings. OGSs are difficult to distinguish from OECTs.

Cranial Nerve Anatomy

The 12 cranial nerves (CNs) all have important functions. All, except the accessory nerve, arise solely within the cranial vault. We will discuss each CN function along with its entire CN course. The modality of choice for evaluation of the CN itself is typically MRI, however, CT is very important to access the bony foramina and CN boundaries..

Olfactory nerve schwannoma: how human anatomy and electron microscopy can help to solve an intriguing scientific puzzle

Schwannomas of the olfactory nerve are rare tumors: to the best of our knowledge, 56 cases have been previously reported. Here we describe a new patient presenting with an isolated olfactory schwannoma, highlighting the importance of multiple ancillary tests to approach the intracranial lesion of the anterior skull base, including electron microscopy. We also discuss the enigmatic origin of this entity, moving from the normal histology of the olfactory nerve compared to a peripheral nerve.

Management of non-vestibular schwannomas in adult patients: a systematic review and consensus statement on behalf of the EANS skull base section. Part I: oculomotor and other rare non-vestibular schwannomas (I, II, III, IV, VI)

BACKGROUND

Non-vestibular schwannomas are relatively rare, with trigeminal and jugular foramen schwannomas being the most common. This is a heterogeneous group which requires detailed investigation and careful consideration to management strategy. The optimal management for these tumours remains unclear, and there are several controversies. The aim of this paper is to provide insight into the main principles defining management and surgical strategy, in order to formulate a series of recommendations.

METHODS

A task force was created by the EANS skull base section along with its members and other renowned experts in the field to generate recommendations for the surgical management of these tumours on a European perspective. To achieve this, the task force performed an extensive systematic review in this field and had discussions within the group. This article is the first of a three-part series describing non-vestibular schwannomas (I, II, III, IV, VI).

RESULTS

A summary of literature evidence was proposed after discussion within the EANS skull base section. The constituted task force dealt with the practice patterns that exist with respect to pre-operative radiological investigations, ophthalmological assessments, optimal surgical and radiotherapy strategies and follow-up management.

CONCLUSION

This article represents the consensually derived opinion of the task force with respect to the treatment of non-vestibular schwannomas. For each of these tumours, the management of these patients is complex, and for those which are symptomatic tumours, the paradigm is shifting towards the compromise between function preservation and progression-free survival.

Anterior skull base olfactory tumours, which is what? A case report and review

Intracranial schwannomas not originating from cranial nerves are rare. In this paper, we report a case of a 50-year-old male who presented with worsening headaches, diplopia and nausea over two years. Radiological imaging revealed a large tumour arising from the olfactory groove region with a preoperative diagnosis of olfactory groove meningioma (OGM). Intraoperatively, the tumour originated from the region of the attachment of the falx to the crista galli. The patient recovered without complication and histopathology reported an unexpected diagnosis of WHO Grade 1 schwannoma. However, as olfactory groove schwannomas (OGSs) cannot be distinguished from olfactory ensheathing cell tumours (OECTs), it is possible that the tumour could have been either an OGS or an OECT. Distinguishing between OGSs, OECTs and OGMs preoperatively is difficult. OGMs exhibit distinct histopathological features from OGSs/OECTs, however, OGSs and OECTs currently cannot be distinguished from each other. Here, we review the literature to discuss the differentiating features and cellular origins of these three tumours.

Why are olfactory ensheathing cell tumors so rare?

The glial cells of the primary olfactory nervous system, olfactory ensheathing cells (OECs), are unusual in that they rarely form tumors. Only 11 cases, all of which were benign, have been reported to date. In fact, the existence of OEC tumors has been debated as the tumors closely resemble schwannomas (Schwann cell tumors), and there is no definite method for distinguishing the two tumor types. OEC transplantation is a promising therapeutic approach for nervous system injuries, and the fact that OECs are not prone to tumorigenesis is therefore vital. However, why OECs are so resistant to neoplastic transformation remains unknown. The primary olfactory nervous system is a highly dynamic region which continuously undergoes regeneration and neurogenesis throughout life. OECs have key roles in this process, providing structural and neurotrophic support as well as phagocytosing the axonal debris resulting from turnover of neurons. The olfactory mucosa and underlying tissue is also frequently exposed to infectious agents, and OECs have key innate immune roles preventing microbes from invading the central nervous system. It is possible that the unique biological functions of OECs, as well as the dynamic nature of the primary olfactory nervous system, relate to the low incidence of OEC tumors. Here, we summarize the known case reports of OEC tumors, discuss the difficulties of correctly diagnosing them, and examine the possible reasons for their rare incidence. Understanding why OECs rarely form tumors may open avenues for new strategies to combat tumorigenesis in other regions of the nervous system.

Rare Cranial Nerve Schwannomas: A Retrospective Review of Nontrigeminal, Nonvestibular Cranial Nerve Schwannomas

Introduction:

Intracranial schwannomas arising from non-trigeminal and non-vestibular sources are extremely rare constituting <0.8% of all schwannomas. In this article, we have analyzed our experience in the management of these rare tumors over a 10-year period.

Material and Methods:

There were a total of 16 cases, with 11 of them undergoing microsurgical resection and 5 undergoing stereotactic radiosurgery (SRS).

Results:

There were no fresh neurological deficit in any of these patients and two patients underwent postoperative SRS for residual tumor. One patient died due to postoperative septicemia.

Conclusion:

Knowledge of these lesions along with their clinicoradiological profile is essential to maintain a high index of suspicion and understand the nuances of treatment.

Olfactory Nerve Schwannoma: A Case Report and Review of the Literature

Schwannomas are benign tumors, which arise from the Schwann cells of the central or peripheral nerves. They form 8% of all intracranial tumors and most of the cases arise from vestibular division of the 8 ^th cranial nerve. Rare cases are shown to arise from the olfactory or optic nerve, being devoid of myelin sheath. Up to date and according to our best of knowledge, 66 cases have been reported till now. Here we present a review of the literature and a case report of a 56-year-old male with an accidently discovered anterior cranial fossa schwannoma, following a road traffic accident. Tumor was completely excised, using a right frontal approach. Histopathology revealed Antoni-A cellular pattern. Although rare, but olfactory nerve schwannomas should be included in the differential diagnosis in anterior cranial fossa space occupying lesions, and the approach should be designed taking into consideration, this rare entity.

Imaging review of the anterior skull base

The anterior skull base (ASB) is intimately associated with the unique soft tissue subtypes of the nasal cavity, paranasal sinuses, orbits, and intracranial compartment. Pathology involving the ASB is rare but the causes are manifold and can be broadly subdivided into those intrinsic to the skull base and processes extending from below or above. Sinonasal pathology is the most commonly encountered and poses significant management challenges that rely heavily on accurate interpretation of the radiological findings. We illustrate the normal anatomy of the ASB and present a cross-sectional imaging review of the pathological entities that may be encountered, focusing on the specific features that will impact on clinical and surgical management.

Frontoethmoidal Schwannoma with Exertional Cerebrospinal Fluid Rhinorrhea: Case Report and Review of Literature

BACKGROUND

Frontoethmoidal schwannomas are rare. No case manifesting exertional cerebrospinal fluid (CSF) rhinorrhea has ever been reported to the best of our knowledge.

CASE DESCRIPTION

In this report, we describe an extremely rare case of frontoethmoidal schwannoma extending through the olfactory groove with exertional CSF rhinorrhea as the initial symptom. A 50-year-old woman was presented to our clinic for frequent nasal discharge on exertion. A postcontrast computed tomographic scan demonstrated heterogeneously enhanced tumor from the anterior cranial fossa to the anterior ethmoid sinus. A gadolinium-enhanced T1-weighted magnetic resonance image revealed a well-defined heterogeneously enhanced tumor situated in the midline anterior cranial fossa and anterior ethmoid sinus. After the resection, the defect of the right anterior skull base was reconstructed with a fascia graft and adipose tissue taken from the abdomen, as well as a pedicle periosteum flap. A histologic examination revealed the tumor as schwannoma. Her rhinorrhea completely resolved. She regained her sense of smell and taste 1 month after the operation.

CONCLUSION

According to previous reports, olfactory groove, and paraolfactory groove/periolfactory groove schwannomas can be divided into 4 types: subfrontal, nasoethmoidal, frontoethmoidal, and ethmofrontal. Among them, a frontoethmoidal schwannoma can manifest exertional CSF rhinorrhea as an initial symptom.

Subfrontal Schwannoma: Case Report and Review of Literature

BACKGROUND

Although attributing the origin of schwannomas from the olfactory nerve is nearly impossible, if they do not have Schwann cells, intracranial supratentorial schwannomas are mainly located in the anterior skull base.

CASE DESCRIPTION

We present the case of a 46-year-old female who presented with right tinnitus, dizziness, and bifrontal headache, progressive, starting 2 years before. Imaging studies revealed an incidentally neoplastic, extraaxial, homogeneously appearing tumor on the right anterior skull base. The patient underwent surgical treatment with total resection of the tumor by a bicoronal approach. The histopathologic study reported schwannoma.

CONCLUSION

We describe this case in detail and discuss the likely origin of this tumor, with a concomitant literature review.

Schwannoma-like tumor in the anterior cranial fossa immunonegative for Leu7 but immunopositive for Schwann/2E

Schwannoma arising from the olfactory system, often called olfactory groove schwannoma (OGS), is rare, as the olfactory bulb and tract, belonging to the central nervous system, should lack Schwann cells. Another rare entity called olfactory ensheathing cell tumor (OECT) has been reported, which mimics clinical and radiological characteristics of OGS. Here, we report two rare cases of schwannoma-like tumor in the anterior cranial fossa that showed negative staining for Leu7, but positive staining for Schwann/2E, and discuss their origin. Two cases of mass lesions in the anterior cranial fossa in a 26-year-old man and a 24-year-old woman were successfully removed. Morphological examination of these tumors was compatible with a diagnosis of schwannoma. Immunohistochemically, both cases were negative for Leu7, yielding a diagnosis of OECT, but were positive for the schwannoma-specific marker, Schwann/2E. Immunohistochemical staining results in our two cases question the current assumption that OGS and OECT can be distinguished only by Leu7 staining pattern. In conclusion, the origins of OGS and OECT remain to be determined, and further studies in larger numbers of cases are needed to characterize these rare tumors in the anterior cranial fossa.

Globose, cystic olfactory ensheathing cell tumor: A case report and literature review

Olfactory ensheathing cell tumor (OECT) is one of the most rare intracranial, extra-axial tumors located in the anterior cranial fossa. The present study reports a case of a 34-year-old female patient who presented with a history of hyposmia for 1 year, as well as a gradual dizziness and emotional lability for 2 months. Magnetic resonance imaging of the brain revealed a globose, well-defined cystic mass at the midline of the anterior cranial fossa, which was confirmed as an OECT by histology and was completely resected by bifrontal craniotomy. According to the immunostaining results, the tumor was positive for vimentin and S100 protein, and negative for epithelial membrane antigen, glial fibrillary acidic protein and cluster of differentiation 57 (also known as Leu-7). The presentation, imaging findings, histopathological examination and histogenesis of OECT are discussed in the present study, along with a literature review.

Cranial Nerve Schwannomas: Diagnostic Imaging Approach

Schwannomas are benign nerve sheath tumors that may arise along the complex course of the cranial nerves (CNs), anywhere in the head and neck. Sound knowledge of the CN anatomy and imaging features of schwannomas is paramount for making the correct diagnosis. In this article, we review approaches to diagnosing CN schwannomas by describing their imaging characteristics and the associated clinical presentations. Relevant anatomic considerations are highlighted by using illustrative examples and key differential diagnoses categorized according to regions, which include the anterior skull base, orbit, cavernous sinus, basal cisterns, and neck. The clinical presentations associated with CN schwannomas vary and range from no symptoms to symptoms caused by mass effect or CN deficits. Individuals with the inherited disorder neurofibromatosis type 2 are predisposed to multiple schwannomas. When a lesion follows the course of a CN, the radiologist's roles are to confirm the imaging features of schwannoma and exclude appropriate differential considerations. The characteristic imaging features of CN schwannomas reflect their slow growth as benign neoplasms and include circumscribed margins, displacement of local structures, and smooth expansion of osseous foramina. These neoplasms exhibit various degrees of solid enhancement, often with internal cystic spaces on magnetic resonance (MR) and computed tomographic (CT) images and heterogeneous high signal intensity specifically on T2-weighted MR images. Clinical and/or imaging evidence of end-organ compromise of the involved CN may exist and aid in the identification of the nerve of origin. With a detailed understanding of the course of the CNs, the diagnostic features of CN schwannomas, and the correlation between these data and the associated clinical presentations of these tumors, the radiologist can have a key role in the diagnosis of CN schwannomas and the treatment planning for affected patients. (©)RSNA, 2016.

An enigmatic clinical entity: A new case of olfactory schwannoma

Olfactory schwannomas, also described as subfrontal or olfactory groove schwannomas, are very rare tumors, whose pathogenesis is still largely debated. We report a case of olfactory schwannoma in a 39-year-old woman who presented with anosmia and headache. The clinical examination did not show lesions in the nose-frontal region and there was no history of neurofibromatosis. Head MRI and CT scan revealed a lobulated extra-axial mass localized in the right anterior cranial fossa that elevated the ipsilateral frontal pole. Bilateral frontal craniotomy demonstrated a tumor strictly attached to the right portion of the cribriform plate that surrounded the right olfactory tract, not clearly identifiable. The immunohistochemical analysis suggested the diagnosis of typical schwannoma. The patient was discharged without any neurological deficit and a four-month postoperative MRI scan of the brain showed no residual or recurrent tumor.

Isolated schwannoma of the olfactory groove: a case report

Introduction Schwannoma of the olfactory groove is an extremely rare tumor that can share a differential diagnosis with meningioma or neuroblastoma.

Objectives The authors present a case of giant schwannoma involving the anterior cranial fossa and ethmoid sinuses.

Case Report The patient presented with a 30-month history of left nasal obstruction, anosmia, and sporadic ipsilateral bleeding. Computed tomography of the paranasal sinuses revealed expansive lesion on the left nasal cavity extending to nasopharynx up to ethmoid and sphenoid sinuses bilaterally with intraorbital and parasellar extension to the skull base. Magnetic resonance imaging scan confirmed the expansive tumor without dural penetration. Biopsy revealed no evidence of malignancy and probable neural cell. Bifrontal craniotomy was performed combined with lateral rhinotomy (Weber-Ferguson approach), and the lesion was totally removed. The tumor measured 8.0 × 4.3 × 3.7 cm and microscopically appeared as a schwannoma composed of interwoven bundles of elongated cells (Antoni A regions) mixed with less cellular regions (Antoni B). Immunohistochemical study stained intensively for vimentin and S-100.

Conclusion Schwannomas of the olfactory groove are extremely rare, and the findings of origin of this tumor is still uncertain but recent studies point most probably to the meningeal branches of trigeminal nerve or anterior ethmoidal nerves.

Two cases of subfrontal schwannoma, including a rare case located between the endosteal and meningeal layers of the dura

Subfrontal schwannomas arising from the olfactory groove are rare and their origin remains uncertain because olfactory bulbs do not possess Schwann cells. We present 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.

Olfactory region schwannoma: Excision with preservation of olfaction

Olfactory region schwannomas are rare, but when they occur, they commonly arise from the meningeal branches of the trigeminal nerve and may present without involvement of the olfaction. A 24 year old lady presented with hemifacial paraesthesias. Radiology revealed a large olfactory region enhancing lesion. She was operated through a transbasal with olfactory preserving approach. This manuscript highlights the importance of olfactory preservation in such lesions.

Two cases of subfrontal schwannoma, including a rare case located between the endosteal and meningeal layers of the dura

Subfrontal schwannomas arising from the olfactory groove are rare and their origin remains uncertain because olfactory bulbs do not possess Schwann cells. We present 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.

Intraarterial schwannoma in horizontal segment of middle cerebral artery causing subarachnoid hemorrhage

A spontaneous subarachnoid hemorrhage (SAH) from the middle cerebral artery is most commonly caused by the rupture of saccular aneurysms and rarely by fusiform aneurysms or arterial dissections/dissecting aneurysms. To the authors' knowledge, this is the first report of an intraarterial neoplasm causing an SAH. A 44-year-old woman presented with an SAH in the basal cisterns. Subsequent internal carotid artery angiography demonstrated a small bulge on the superior wall of the horizontal (M1) segment of the middle cerebral artery. However, a pterional craniotomy revealed a well-circumscribed solitary tumor with a diameter of 15 mm involving the superior wall of the M1 segment as the cause of the SAH. Pathological examination demonstrated typical findings of a schwannoma, elongated cells with tapered, spindle-shaped nuclei and indistinct cell borders, and diffuse immunoreactivity for the S100 protein.

Ethmoidal air cell schwannoma presented as a fronto-ethmoidal mucocele

AIM

To report a rare case of a fronto-ethmoidal mucocele secondary to an ethmoidal schwannoma. To our knowledge this is the first reported case of an ethmoidal schwannoma, a tumour of the peripheral nerve sheath originating from an area not believed to contain peripheral nerves that has presented as a fronto-ethmoidal mucocele.

CASE REPORT

Our patient is a 23-year-old male presented with a one-year history of progressive proptosis and vertical diplopia with restriction of upgaze. Orbital imaging demonstrated a mass in the right medial ethmoidal air cells extending to the frontal sinus and orbit, consistent with a mucocele. Patient underwent endonasal decompression of the right fronto-ethmoidal mucocele. Histology confirmed a schwannoma and repeat imaging post-operatively revealed residual mass originating from the ethmoidal air cells. A right upper eyelid skin crease approach anterior orbitotomy was performed to successfully excise the mass via the lamina papyracea. Post-operatively the patient's proptosis and diplopia resolved, with a full range of ocular movements. Post-operative imagining at 3 months did not show any residual tumour.

COMMENT

Mucocele formation may be secondary to an underlying schwannoma obstructing the fronto-ethmoidal foramen. In such cases we recommend an open-sky technique for full visualisation and improved chance of total removal.