ganglioneuromas are rare benign tumors of neural crest origin ; they arise from peripheral sympathetic ganglia or the adrenal glands .
these tumors are most commonly discovered in older pediatric patients or adults ; they are discovered incidentally , through thoracic or abdominal imaging studies performed for unrelated conditions .
intracranial involvement of ganglioneuromas is extremely rare ( 1 , 2 ) , and there has been only one report of ganglioneuroma arising from the trigeminal nerve .
we report a very rare case of trigeminal ganglioneuroma in the prepontine and cerebellopontine angle cistern , in a 44-year - old female and describe the magnetic resonance ( mr ) imaging characteristics , including diffusion - weighted imaging ( dwi ) findings .
a 44-year - old female was admitted to our hospital because of a 2-year history of facial pain and numbness in the left side .
the patient complained of an intermittent stabbing pain and numbness over the left zygomatic region .
a brain mr imaging study was performed with a 3 t unit ( magnetom triotim , siemens , erlangen , germany ) , which revealed a 2  1.8  1.5 cm well - circumscribed mass in the prepontine and cerebellopontine angle cistern on the left side ( fig .
the left fifth cranial nerve was displaced superomedially , and the seventh - eighth nerve complex inferiorly by the mass .
the mass showed homogeneous iso - signal intensity on a t1-weighted image relative to the brain parenchyma ( fig .
1a ) as well as heterogeneous increased signal intensity on a t2-weighted image ( fig .
the apparent diffusion coefficient ( adc ) values were obtained using a circular region of interest with a diameter of 6 mm at 4 nonoverlapping locations in the tumor ( fig .
the mean adc values obtained with b values of 0 and 1000 sec / mm of the tumor were 0.72  10 mm / s , compared to 3.01  10 mm / s for csf ( measured in the fourth ventricle ) and 0.71  10 mm / s for adjacent brain tissue ( measured in the pons ) .
the preoperative diagnosis for this poorly enhancing mass with a dwi high signal intensity lesion in the prepontine and cerebellopontine angle cistern was an epidermoid cyst .
, a well - circumscribed solid mass was found to be firmly attached to the trigeminal nerve .
histopathologic examination demonstrated a benign tumor composed of mature ganglion cells and spindle - shaped cells in an abundant collagenous stroma ( fig .
postoperatively , facial pain and numbness disappeared , and follow - up mr imaging , obtained 16 months later showed no evidence of tumor recurrence .
ganglioneuromas are typically found within the posterior mediastinum and retroperitoneum , though less common locations include the adrenal medulla , parapharyngeal region , and visceral ganglia .
rarely , ganglioneuromas have been observed in the tongue , prostate , skin , and bone ( 3 ) .
intracranial ganglioneuroma is extremely rare , and only a few cases have been reported in previous literature ( 1 , 2 ) .
histologically , these tumors are composed of single or clustered mature ganglion cells and mature schwann cells ( 3 ) .
typical radiologic findings of ganglioneuroma arising from the peripheral sympathetic nerve have been described . at ct , ganglioneuromas are well - demarcated hypoattenuated lesions , with calcifications in 20 - 42% of cases .
these tumors are not significantly enhanced after the administration of contrast materials , but delayed ct images can show slight or moderate enhancement ( 3 , 4 ) . at mr , ganglioneuromas are generally hypointense on t1-weighted images and heterogeneously hyperintense on t2-weighted images with respect to adjacent muscle .
( 1 ) reported the first case of trigeminal ganglioneuroma and described conventional mr imaging findings , which are similar to those of thoracoabdominal ganglioneuromas . mr images included in their report demonstrated a well - defined mass with low signal intensity on a t1-weighted image , high signal intensity on a t2-weighted image , and relatively homogenous enhancement on a post - contrast t1-weighted image . in our patient ,
the lesion was iso - signal intense to the adjacent pons on the t1-weighted image and showed slightly increased signal intensity on the t2-weighted image .
it has previously been reported that ganglioneuromas with markedly high signal intensity on a t2-weighted image histologically consist of a large amount of myxoid stroma and relatively few cellular components and collagen fibers .
in contrast , tumors with intermediate to subtle high signal intensities on a t2-weighted image , as in our case , consisted of numerous cellular and fibrous components and few myxoid stroma ( 4 , 5 ) . in our case , the mass showed poor enhancement on a postcontrast t1-weighted image .
thoracoabdominal ganglioneuromas can demonstrate gradually increasing enhancement with dynamic mr imaging ( 3 - 5 ) .
diffusion - weighed imaging findings and adc values with regard to intracranial ganglioneuroma have not been published previously .
our case showed a homogeneous hyperintense signal throughout the tumor , on a dwi , and revealed a mean tumor adc value of 0.72  10 mm / s .
( 6 ) recently reported dwi findings of the ganglioneuromas / ganglioneuroblastomas originating from the thoracoabdominal sympathetic nervous system .
these tumors showed relatively high adc values ( mean adc : 1.60  10 mm / s , range 1.13 - 1.99  10 mm / s ) .
the differences between gahr 's cases and our case may be due to the different tumor histopathologies .
one might postulate that high cellular density and scanty myxoid stroma , revealed through histopathology , may be attributed to relatively low adc values in our case .
( 7 ) reported that focal central hemorrhages were observed in 2 of 17 adrenal ganglioneuromas .
our case showed no intratumoral susceptibility signals on gradient echo images , as well as absence of intratumoral hemorrhage or calcification with histopathology .
an epidermoid cyst should be included in the differential diagnosis of t2-increased signal intensity lesions in the prepontine and cerebellopontine angle cisterns .
the high signal intensity of epidermoid cysts with dwi is caused by the intrinsic t2 shine - through effects of the lesion .
reported adc values of intracranial epidermoid cysts range from 0.98  10 mm / s up to 1.36  10 mm / s ( 8) ; these are higher than the values of trigeminal ganglioneuroma in our case .
other differential diagnoses of masses in the prepontine and cerebellopontine angle cisterns include schwannoma , meningioma , neurofibroma , and metastasis .
the majority of these tumors do not show high signal intensity with dwi and demonstrate relatively strong enhancement on post - contrast t1-weighted images .
other rare tumors that have been reported to occur in the trigeminal nerve include benign triton tumor ( neuromuscular hamartoma ) and ganglioglioma .
neuromuscular hamartomas were reported to be profoundly hypointense on t2-weighted images and demonstrated mild homogenous contrast enhancement ( 9 ) .
a trigeminal ganglioglioma may be difficult to distinguish from a ganglioneuroma like that in our case .
this tumor showed a nonspecific homogenous mr signal intensity indistinguishable from the adjacent brain stem with all imaging sequences and no contrast enhancement ( 10 ) .
dwi findings of neuromuscular hamartoma and ganglioglioma , arising from the trigeminal nerve have not been reported .
trigeminal ganglioneuroma is a very rare tumor ; however , this tumor should be considered in the differential diagnosis of tumors with low adc values in the prepontine and cerebellopontine angle cistern .
trigeminal ganglioneuroma is a very rare tumor ; however , this tumor should be considered in the differential diagnosis of tumors with low adc values in the prepontine and cerebellopontine angle cistern .
 a case of intracranial ganglioneuroma arising from the trigeminal nerve in the pontine and cerebellopontine angle cistern , in a 44-year - old female , is presented with an emphasis on diffusion - weighted imaging findings . 
 we will discuss on how the tumor in the very unusual location should be differentiated particularly focused on diffusion - weighted imaging findings . 