An olfactory groove meningioma is a rare benign tumor with a rather insidious course. Most common symptoms are anosmia, headaches, and visual disturbances, but a range of manifestations, both neurologic and psychiatric, has been described in a significant number of patients. Clinical suspicion towards intracranial neoplasms must be raised when longstanding signs are present, whereas confirmation is achieved through imaging studies, such as magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), and MR spectroscopy.
Encompassing approximately 12% of all meningiomas in the base of the skull, an olfactory groove meningioma (OGM) arises from the arachnoidal cells located in the lamina cribrosa of the ethmoid bone and frontosphenoidal suture [1] [2] [3]. One of the most important features of OGM is its frequent delay in the diagnosis due to lack of clinical suspicion despite the presence of typical symptoms and up to 3 years may pass before the condition is recognized [3] [4] [5]. Anosmia and headaches are considered to be the primary signs [1] [2] [6], but they are often misdiagnosed as sinusitis, migraines or neuralgia [6]. Moreover, visual deficits (hypophthalmos, visual acuity impairment, and vision loss), nasal obstruction, hyposmia, epistaxis, and papilledema may be seen [3]. In up to a third of cases, psychiatric complaints in the form of disinhibition, psychosis, personality changes, confusion, or even cognitive decline (eg. memory loss) are noticed [1] [3] [5] [7]. In advanced stages of tumor development, the appearance of seizures is common, whereas hemiparesis is also observed in a number of sufferers [3]. For still unknown reasons, the majority of case studies in the literature have identified a significant predominance towards female gender [1] [3] [7].
Given the slowly progressive and underrecognized nature of OGM, it is essential to perform a comprehensive and meticulous workup. Firstly, a detailed patient history that will assess the course and progression of symptoms should be obtained, followed by a thorough physical examination, with a particular emphasis on the neurological examination. However, olfactory testing frequently yields normal findings, thus the typical clinical picture might be absent [2]. To determine the underlying etiology (but also to plan the optimal therapeutic strategy), imaging studies need to be employed. Computed tomography (CT), although sometimes sufficient to make the diagnosis [5], has shown to be of limited use in the assessment of olfactory groove meningioma (particularly in the postoperative setting when patients are checked for tumor recurrence) [4]. For this reason, MRI (sometimes with gadolinium contrast enhancement) is the recommended study, showing an isointense or slightly hypointense signaling on T1-weighted studies and a hyperintense signal on T2-weighted studies compared to the cerebral cortex in the case of OGM [3] [8]. Because meningiomas have a wide differential diagnosis, additional exams, such as diffusion-weighted imaging, diffusion tensor imaging (DT), and MR spectroscopy are frequently used to further solidify the diagnosis [8].