Discussion

WHO grades meningiomas on a scale from I to III where I is benign, II being atypical and III representing anaplastic/ malignant. Majority of the meningiomas are WHO grade I. Atypical and anaplastic meningiomas can be distinguished from type I (benign) by histopathology. Olfactory groove meningiomas account for 8 to 13% of all intracranial meningiomas. OGMs are commonly diagnosed when their size is significant and causes local pressure effect. The initial symptoms of many patients are nonspecific and slow in progression. Many individuals have asymptomatic meningiomas that have been discovered only during an autopsy. 1% to 2% of all autopsies reveal meningiomas that were unknown to the individuals during their lifetime [2,3,11]. In the 1970s, tumors causing symptoms were discovered in 2 out of 100,000 people, while tumors discovered incidentally occurred in 5.7 out of 100,000. With the advent of modern sophisticated imaging systems such as CT scans and MRI, the discovery of asymptomatic meningiomas has tripled [11]. Anosmia is one of the earliest presenting complaints, At the time of diagnosis, anosmia is noted in more than 50% of cases [4]. Later on the patients start complaining of headaches and personality changes, such as apathy and akinesia, which are commonly misleading as being associated with depression or aging. Rarely, Seizures as well as aggressiveness which has been reported as a result of frontal lobe dysfunction in some studies. Later stages of this disease can lead to dementia, urinary incontinence, nasal obstruction and epistaxis, spontaneous Cerebrospinal Fluid (CSF) leaks due to its local invasion in the paranasal sinuses add to that the visual problems resulting from compression of the optic nerve or optic chiasm or intraorbital invasion of the tumor. Less frequently patient with OGM presented as case of Foster Kennedy syndrome in which the triad of anosmia and unilateral optic atrophy with contralateral papilledema are observed simultaneously [5,12,13].

The causes of this mass is not well known. Some scientific studies indicating that the Genetic alterations play an important role. The most frequent genetic mutations about 50% involved in meningiomas are inactivation mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q. Other mutations such as TRAF7 are present in about 25% of meningiomas. Mutations in the TRAF7, KLF4, AKT1, and SMO genes are commonly expressed in benign skullbase meningiomas. Mutations in NF2 are commonly expressed in meningiomas located in the cerebral and cerebellar hemispheres [14].

The differential diagnosis of a large and enhancing subfrontal mass in adult are olfactory groove meningiomas and subfrontal schwannomas. Schwannomas of the ethmoidal nerve are very rare and it is hard to be distinguished from meningiomas by imaging only [4]. One of the reported studies mentioned that the distinction point between schwannoma and meningioma is the nearby bone state. Schwannomas cause a little more bony erosion, whereas meningiomas tend to cause hyperostosis. Furthermore subfrontal schwannomas were exceeding rarely reported so we did not expect this tumor to be a schwannoma [5]. Neuroblastoma, squamous cell carcinoma, adenocarcinoma, and metastases should also be considered in the differential diagnosis in adults with a tumor involving both the nasal cavity [12,13].

Imaging is useful in making the diagnosis and to evaluate suspected intracranial tumors. Although MRI is the imaging test of choice as it reveals the soft tissue tumors, meningiomas should be seen using Computed Tomography (CT scan) using contrast as well. The CT scan shows any associated bony hyperostosis while bony involvement is important to determine, as it highly contribute to tumor recurrence [8,15]. Olfactory groove meningiomas tend to have a rather high rate of recurrence (30% at 5 years and 41% at 10 years), which is mainly because incomplete resection, particularly of the involved underlying bone at the cranial base [16-18].

Many different surgical interventions have been recommended based on evidence of cure. Resection has traditionally been performed using a bifrontal or pterional approach, both of which require some degree of brain retraction or manipulation to expose the tumor that affecting the general outcomes [18-20]. On the other hand, the purely endoscopic endonasal transcribriform approach that has been done and reported in certain studies. This approach as they had mentioned offers a direct midline trajectory and immediate access for removal of olfactory groove meningiomas without brain retraction and manipulation of neurovascular structures. Extracapsular dissection with preservation of the arachnoid planes can be achieved using bimanual microsurgical techniques through a keyhole craniectomy directed at the ventral skull base. In carefully selected patients, complete Simpson Grade I tumor removal including the dural attachment and involved hyperostotic bone can be achieved. Excellent panoramic visualization of the entire ventral skull base extending from the posterior wall of the frontal sinus to the planum sphenoidale can be obtained with a 30° endoscope after performing a modified Lothrop procedure. Successful cranial base reconstruction can be performed using a multilayer fascia lata and AlloDerm technique supplemented by bilateral vascularized nasoseptal flaps. During the surgical operation, the adjacent paranasal sinuses increases the risk of CSF leakage and meningitis [18,20-22]. Thus, most surgeons have taken a more conservative approach, usually prefer to use a Simpson Grade II resection, without aggressive resection of the involved bone at the cranial base to avoid these complications. However, cauterization of the dural or resection alone without removal of bone involvement leads to high rate of recurrence [6,7,22].