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. 2010 Jul 26;21(1):31–36. doi: 10.1055/s-0030-1262945

The Puzzling Olfactory Groove Schwannoma: A Systematic Review

Eberval Gadelha Figueiredo 1, Yougi Soga 2, Robson Luis Oliveira Amorim 1, Arthur Maynart Pereira Oliveira 1, Manoel Jacobsen Teixeira 1
PMCID: PMC3312416  PMID: 22451797

Abstract

We systematically reviewed the literature concerning the anterior cranial fossa schwannomas to understand their pathogenesis, determine their origin, and standardize the terminology. We 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.

Keywords: Anterior cranial fossa, olfactory groove, olfactory nerve, schwannomas, subfrontal tumors

Schwannomas are benign, slowly growing nerve sheath tumors.1,2,3,4 They account for ∼8% of all intracranial tumors and can arise from any nerve containing Schwann cells.4,5,6,7 The most common location is the vestibular portion of the VIIIth cranial nerve and, less commonly, the Vth, IXth, Xth, and VIIth cranial nerves.4,5,6,7,8,9 The occurrence of a schwannoma not related to cranial nerves is exceedingly rare, with the most common location being the anterior cranial fossa. In such instances, they have been described under different designations, such as subfrontal, olfactory, and olfactory groove schwannomas,1,2,3,4,5,6,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28 reflecting their enigmatic origin. However, these terminologies have contributed to the confusion concerning pathogenesis and have created a great deal of speculation about it. It is still not clear which type of cell gives rise to these schwannomas and even whether they are derived from the cerebral parenchyma.4 This uncertainty is partially due to the incompleteness of the previous literature reviews, which have provided only limited contribution. To address these issues, the authors performed a systematic review of the literature.

METHODS

The authors first performed a MEDLINE, EMBASE, and Science Citation Index Expanded search of the literature of the last 30 years with the use of four key words in all relevant combinations: schwannoma, olfactory, olfactory groove, and anterior cranial fossa.

Additionally, the reference lists of all retrieved publications were scrutinized. The references of the publications thus found were checked again for additional studies. This method of cross-checking was continued until no further publications were found.

Inclusion and Exclusion Criteria

Papers reporting anterior fossa schwannomas published in English, Japanese, German, Spanish, and Portuguese were reviewed. Data such as age, gender, clinical presentation, presence or absence of hyposmia, radiological features, and apparent origin were analyzed and tabulated. Site of origin was defined by radiological features coupled with surgical description, when this information was available. Studies reporting autopsy cases in a context of neurofibromatosis were excluded from the review. Papers describing nasal schwannomas with intracranial extension were also not included.

RESULTS

This systematic review is summarized in Table 1. Thirty-three cases of anterior fossa schwannomas were identified.

Table 1.

Thirty-Three Cases of Anterior Fossa Schwannomas were Identified in the Literature

Author Age/Gender Clinical Presentation Anosmia Radiological Features Origin Olfactory Tract
Figueiredo et al, 200928 49/M Headache Yes Cystic, heterogeneous Olfactory groove Thinned
Choi et al, 200926 39/M Headache Yes Cystic, heterogeneous Olfactory groove Involved
Adachi et al, 20071 22/F Seizures No Solid, heterogeneous Olfactory groove Thinned
Prak et al, 200627 16/M Headache, diplopia No Solid, heterogeneous Olfactory groove Not Involved
Yako et al, 20057 14/M Headache Yes Solid, heterogeneous Olfactory groove Not seen
Shenoy and Raja 200421 55/M Seizures No Cystic, heterogeneous Olfactory groove Thinned
Murakami et al, 200416 30/M Headache No Solid, homogeneous Olfactory groove Thinned
Komoribayashi et al, 20045 37/F Seizures Yes Solid, homogeneous Olfactory groove Not seen
Yuen et al, 200429 33/F Seizures NO Solid, homogeneous Olfactory groove Involved
Prasad et al, 200419 19/M Seizures Yes Solid, heterogeneous Olfactory groove Unreported
de Souza et al, 200312 27/M Headache Yes Cystic, homogeneous Olfactory groove Unreported
Amador et al, 200210 24/F Hypoesthesia, visual deficit Unreported Cystic, heterogeneous Olfactory groove Not seen
Carron et al, 20023 59/F Headache, rhinorrhea No Solid, homogeneous Olfactory groove Involved
Yang et al, 200225 55/M Headache No Solid, homogeneous Olfactory groove Unreported
Tsai et al, 200124 31/F Seizures, headache Unreported Solid, heterogeneous Olfactory groove Unknown
Tan et al, 200122 21/M Seizures No Solid, homogeneous Olfactory groove Unreported
Gelabert et al, 200013 19/M Seizures No Solid, homogeneous Olfactory groove Unreported
Timothy et al, 199923 33/F Seizures No Solid, homogeneous Olfactory groove Not seen
Praharaj et al, 199924 45/M Seizures, headache Unreported Solid, homogeneous Olfactory groove Not seen
Boyd et al, 199711 29/F Seizures, headache Yes Cystic, heterogeneous Olfactory groove Involved
Huang et al, 199732 33/M Headache, visual deficit No Solid, homogeneous Olfactory groove Unknown
Sabel and Teepen 19954 17/M Seizures Unreported Solid, homogeneous Olfactory groove Not seen
Harada et al, 199214 33/M Headache Yes Solid, heterogeneous Olfactory groove Thinned
Husain et al, 19929 30/M Headache Yes Unreported Olfactory groove Not seen
Bando et al, 19928 55/F Visual deficit Yes Mixed, homogeneous Undefined Not seen
Nagao et al, 199117 63/F Memory impairment No Cystic, heterogeneous Olfactory groove Unreported
Sato et al, 198520 22/M Seizures Yes Solid, homogeneous Olfactory groove Thinned
Mauro et al, 198339 44/M Visual and memory deficits Unreported Cystic, heterogeneous Olfactory groove Unreported
Vassilouthis and Richardson 198037 17/M Visual and cognitive deficit Yes Cystic, heterogeneous Olfactory groove Unreported
Ulrich et al, 197838 19/M Seizures, visual deficits Yes Unreported Olfactory groove Not seen
Harano et al, 197415 26/F Seizures No Cystic Skull base Distant
Viale et al, 197336 22/M Visual deficits Yes Unreported Olfactory groove Unreported
Strum et al 196840 27/M Headache Yes Unreported Olfactory groove Not seen
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Age, Gender, and Clinical Presentation

Age varied between 14 and 63 years (mean = 30.9). There were 22 male (66.6%) and 11 female (33.3%) patients. Clinical presentation included seizures, the most common finding (n = 15; 45% of the cases); headache (n = 16; 48% of the cases); visual deficits (n = 7; 21.2% of the cases); cognitive disturbances (n = 3; 9% of the cases); and rhinorrhea (n = 1; 3% of the cases). Anosmia/hyposmia was present in 14 cases (42.4%), absent in 13 cases (39.3%), and unreported in 5 cases (15.1%). Therefore, anosmia/hyposmia was absent in 54.4% of the cases in which this information could be retrieved.

Radiological Features and Apparent Origin

Tumor was solid in 19 patients (57.5%) and cystic in 10 (30.3%). Radiological appearance was unreported in 5 cases (15.1%). Homogeneous and heterogeneous contrast enhancement was observed in 14 (42.4%) and 15 cases (45.4%), respectively. Enhancement was not reported in five patients (15.1%).

In most of the cases (n = 31; 93.9%), the lesion was located in the midline with close relationship with the olfactory groove. In just one case, the lesion was not clearly related with the olfactory groove. In one case, the origin could not be determined, as the author described a recurrence of the primary tumor. Therefore, the region of the olfactory groove was the apparent origin in 96.5% of all cases where the origin was clearly reported.

Olfactory Tract

Olfactory tract was identified but involved in six cases (18.1%), individualized and thinned in six (18.1%), and distant from the tumor in one (3.4%). Olfactory tract was not identified in 10 cases (34%). The involvement of the olfactory tract was unreported in 11 cases (33.3%). Olfactory tract could be identified in 39.3% (n = 13) of the cases that reported its status.

DISCUSSION

Intracranial schwannomas unrelated to the cranial nerves are extremely uncommon.5,6,7,16,29 They occur more frequently in the anterior cranial fossa, mainly in the midline. In these instances, they have been described as subfrontal schwannomas, olfactory schwannomas, or olfactory groove schwannomas.1,2,3,4,5,6,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28 These different terminologies, associated with their rarity and enigmatic origin, further complicate the study of intracranial schwannomas.1,2,4 Schwannomas mainly arise from nerve sheaths of peripheral and cranial nerves (except for first and second cranial nerves). However, the pathogenesis of intracranial schwannomas not directly associated with cranial nerves has been puzzling.1,2,3,4,5,6,7 Additionally, considerable debate exists whether these schwannomas are primarily intra- or extra-axial lesions.1,2,4

There are several hypotheses concerning their probable origin. Developmental theories advocate that these lesions primarily arise from aberrant Schwann cells in the central nervous system.1,4 Russel and Rubinstein30 have proposed that mesenchymal pial cells may transform into ectodermal Schwann cells, explaining the occurrence of intraparenchymal schwannomas. Additionally, peripheral-type myelin has been found in pathological conditions such as multiple sclerosis and cerebral infarctions, presumably originating from Schwann cells in the central nervous system.31 Other theories suggest an origin from multipotential mesenchymal cells or displacement of neural crest cells forming the focus of Schwann cells within brain parenchyma (schwannosis).30

These developmental theories adequately explain the origin of intraparenchymal schwannomas.1,2,4,32 However, the subtype of schwannomas located in the base of the frontal lobe and intimately related to the olfactory groove seems to be extra-axial rather than intra-axial lesions.1,2,3 Even though some authors have proposed a developmental origin for explaining the occurrence of these lesions,4 they present several features that point the pathogenesis in another direction.

Adachi et al1 performed an extensive review of the literature and postulated that these tumors originate from the fila olfactoria. The embryonic terminal nerve, the nerve plexus of dural vessels, and the fila olfactoria that acquire Schwann cells ∼0.5 mm beyond the olfactory bulb have also been considered as possible origins.1,33 Others authors2,3,4,24,26,32 have pointed out that olfactory schwannomas originate from the olfactory bulb and nerve. However, the olfactory bulbs and tracts lack Schwann cells and hence cannot give rise to the tumor. Although a kind of “ensheathing cell” that expresses phenotypic features of both astrocyte and Schwann cell is present,34 it is still an open question whether or not such a cell may generate a schwannoma.

Schwann cells are normally present within the perivascular nerve plexuses around large arteries in the subarachnoid space and in adrenergic nerve fibers of cerebral arteries.35 In addition, Schwann cells are found in nerves, such as meningeal branches of trigeminal nerves and anterior ethmoidal nerves, innervating the anterior fossa and olfactory groove.36

Most of the descriptions point to a lesion intimately related to the skull base, particularly to the olfactory groove (97%). Neural structures in the olfactory groove and cribriform plate include olfactory nerve and bulb, fila olfactoria, branches of trigeminal nerve, anterior ethmoidal nerves, and nerve plexus of dural vessels. Hence, they represent the probable origin of this subset of schwannomas. The absence of anosmia/hyposmia in almost half of the cases (54.4%) and the individualization of the olfactory tract in 36.3% of cases make improbable an origin from olfactory bulb and nerves and fila olfactoria and favor an extra-olfactory origin. The fact that the olfactory nerve and bulb were not seen at surgery in 55% of the cases may not necessarily corroborate these structures as the site of origin. They could just be involved by the tumor due the proximity. The predominant midline occurrence practically excludes their origin from vascular dural plexus, as they are not equally distributed in the entire extension of the anterior fossa. Considering these findings, meningeal branches of trigeminal nerve and anterior ethmoidal nerves are the most probable origin of these tumors in the olfactory groove.

CONCLUSION

Anterior cranial fossa schwannomas are very rare tumors, with 33 cases described so far. The findings of this systematic review make improbable an origin from the olfactory tract, including the fila olfactoria, as well as a developmental theory. This review has demonstrated that the most probable origin is the meningeal branches of trigeminal nerve or anterior ethmoidal nerves. Thus, subfrontal or olfactory seems to be inadequate terminology. Olfactory groove schwannoma would better describe its origin and pathogenesis and should be the term preferentially used to describe it.

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