Key-words:
Cerebellopontine angle - exostosis - internal acoustic canal - osteoma
Introduction
Osteoma and exostoses are rare and benign lesions, which grows slowly.[[1]],[[2]] Osteomas are mostly placed at facial bones, mandibular bones, and calvarial bones.[[3]] They also tend to be found in the mastoid cortex and external acoustic canal (EAC)
of temporal bone; however, more rarely, they can be found in internal acoustic canal
(IAC) and cerebellopontine angle (CPA).[[1]],[[3]] Even though neuronal tissue involvement leads to neurologic problems, they are
mostly diagnosed incidentally. To our knowledge, only one case has been reported with
bilateral osteoma located in CPA and another case has been reported with bilateral
osteoma, which lead to IAC obstruction.[[2]],[[4]] We report on a case presented with headache and bilateral osteomas in CPA diagnosed
incidentally and discuss the management of such cases.
Case Report
A 75-year-old woman, with a 1-year history of headache, was admitted to the Department
of Neurosurgery, Kayseri Training and Research Hospital, in December 2012. Patient's
headache had relieved partially under long-term medical treatment. Brain magnetic
resonance imaging (MRI) was planned to identify the possible etiology of chronic headache.
Brain MRI revealed bilateral extra-axial bony masses in IAC, which were placed at
the superior edge at right and posterior edge at left. Lesions were hypointense in
axial T2-weighted MRI. Cranial computed tomography images were obtained to identify
osseous nature of lesions [[Figure 1]]. Even though there was no neurologic deficit, audiometry was done and no abnormality
was found. The lesions were too small for operation, so we proposed conservative treatment
instead of operation. Our diagnosis did not depend on histopathological findings.
Control MRI was planned to follow-up possible progression. Unfortunately, the patient
did not come back to our clinic, so we could not have follow-up data.
Figure 1: Initial presentation of the patient. Bilateral cerebellopontine angle masses were
hypointense to cerebrospinal fluid in axial T2-weighted imaging (a-c), and hyperdense
bony lesions were shown in cranial computed tomography scan (d-f)
Discussion
Definition and pathology
Osteoma and exostoses located in IAC and CPA have been reported very rarely, and differential
diagnosis should be done from each other.[[1]],[[2]],[[3]],[[4]],[[5]],[[6]],[[7]],[[8]],[[9]],[[10]],[[11]],[[12]],[[13]],[[14]],[[15]],[[16]],[[17]],[[18]],[[19]],[[20]],[[21]] Osteomas mostly arise from IAC and develop in CPA. They tend to be found in the
mastoid cortex and EAC at temporal bone.[[2]],[[5]] In addition, they were found in mastoid air cells and middle ear.[[2]]
Osteomas generally are isolated, pedunculated, dense, homogeneous bony development.
They are well demarcated that can be circular or multilobular.[[3]] They usually involve tympanosquamous or tympanomastoid sutures.[[2]],[[3]] Histopathologic examination shows irregularly oriented lamellate bones encircling
highly fibrovascular channels. Reactive metaplastic ossification centers are present.[[2]],[[3]] Contrary, exostoses usually tend to be multiple and bilaterally symmetrical. They
involve tympanic bone and are histologically characterized by parallel layers of subepitelial
bony layers.[[2]],[[5]] Genetic defects, developmental diseases, inflammation, and bone injury may lead
to both pathologies.[[2]],[[6]]
Clinic presentation
Osteoma and exostoses of CPA are usually asymptomatic and diagnosed incidentally.[[2]],[[3]],[[7]],[[8]] They are stable even for long time follows because of their slow-growing nature.[[2]] These tumors can cause symptoms related to brain stem compression and the 7th and
8th cranial nerve involvement, such as sensorineural hearing loss, tinnitus, vertigo,
ataxia, and findings related to brain stem compression.[[2]]
Diagnostic imaging and evaluation
The differentiation of CPA osteoma from exostoses usually has been reported by CT
and MRI examination.[[2]] Even though MRI and high-resolution CT scan could help to differentiate, histopathologic
examination is gold standard for diagnosis.[[1]],[[2]]
The differentiation of CPA osteomas and exostoses from other bony lesions involving
IAC such as Paget's disease, fibrous dysplasia, and osteosclerosis must be considered.[[3]] Furthermore, CPA lesions should be reminded that might cause similar symptoms.
Management and prognosis
Few case reports have been published in literature, and besides, there are only two
case reports of bilateral CPA osteoma. First, Gerganov et al. reported bilateral CPA
osteoma that left-sided osteoma excised totally through retrosigmoid approach because
the patient had symptoms related to vestibulocochlear nerve compression. The symptoms
improved after surgery. Ciorba et al. reviewed 19 patients including literature and
own patients. Thirteen patients had osteoma located in IAC, three had exostoses, and
three had no information about pathology of lesions. Eleven patients had undergone
surgery.[[2]]
To our knowledge, 27 cases have been reported with osteoma and exostoses located in
CPA in respect of March 2013. These two lesions reviewed together because only 11
patients had undergone surgery, and eight patients had osteoma and three had exostoses.
Furthermore, differential diagnosis is not always possible with radiologic imaging.
Twenty-seven patients had been reviewed according to their radiological prediagnosis
and histopathologic diagnosis if existed. Osteoma diagnosed in 20 patients and exostoses
diagnosed in 6 patients. However, there was no information for one patient. Six patients
were asymptomatic and followed by conservative treatment. Nineteen patients were symptomatic
and 11 patients underwent surgery and 7 patients were treated by medical therapy.[[2]],[[9]]
There is no particular indication universally shared on how to treat for osteoma and
exostoses of CPA. Ciorba et al. advice to long-term follow-up with neurologic and
audiovestibular examination and CT scan for asymptomatic patients.[[2]] Although successful surgical interventions such as middle fossa approach, retrosigmoid
approach, or suprapetrosal approach have been described, symptoms might persist after
surgery due to chronic compression.[[3]],[[10]] Suprapetrosal approach allows drilling and exposure of IAC, but facial nerve in
this exposure might be injured because of its superficial location.[[3]]
Conclusions
In patients presenting with atypical headache or lower cranial nerve deficits, CPA
osteomas or exostoses should be considered in diagnostic workup. Further radiological
investigations are helpful for correct diagnosis. Conservative treatment should be
tried at first in asymptomatic patients. Surgery should be considered only in symptomatic
and enlarging osteomas.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
