Keywords
mature teratoma - petrous - temporal bone - cerebellopontine angle - resection - child
- pediatric
Introduction
Intracranial germ cell tumors are frequently diagnosed in children and typically arise
from midline locations such as the suprasellar and pineal regions.[1]
[2]
[3] Advancements in neuropathology, neuroradiology, and microsurgical techniques have
allowed for improved diagnosis and treatment of pediatric teratomas. In this paper,
the authors present a case of an 11-year-old girl with 12 months of progressive left-sided
facial weakness. Imaging revealed a large temporal bone mass with extension into the
cerebellopontine angle. A transtemporal approach was undertaken, and the pathology
was consistent with a mature teratoma. To the authors' knowledge, this is the first
case report of a mature teratoma originating in the petrous bone with extension into
the cerebellopontine angle.
Case Report
History and Examination
A previously healthy 11-year-old girl began experiencing left-sided facial weakness
12 months before presentation; her parents noted obvious asymmetry over the last 3
months along with daily headache. Past medical history was notable for congenital
unilateral deafness (left-sided), but no previous imaging or further evaluation of
this deficit had been pursued. Neurologic examination revealed multiple mid to lower
cranial nerve deficits. She had limited abduction of the left eye, a House-Brackmann
grade V/VI left-sided facial palsy, absent elevation of the left soft palate, and
deviation of the tongue to the left. The patient had profound hearing loss in the
left ear on audiologic evaluation. Results of motor, sensory, cerebellar, and gait
testing were normal.
Imaging
Computed tomography (CT) demonstrated a multiloculated lesion expanding the labyrinthine
structures in the left petrous temporal bone including the vestibule, semicircular
canals, and cochlea, with extension to the left cerebellopontine angle via the expanded
left internal auditory canal ([Fig. 1]). There was no overt osseous destruction. A punctate intralesional calcification
and at least two small foci of fat were evident. There was significant mass effect
on the left pons, middle cerebellar peduncle, and cerebellum. Magnetic resonance (MR)
imaging at 3-Tesla (Magnetom Trio, Siemens, Erlangen, Germany) confirmed these features
and demonstrated a cerebrospinal fluid (CSF) signal intensity, diffusion-restricted
component that was consistent with epidermoid cyst in the left prepontine cistern
and compression of the left fifth cranial nerve between the cyst and the rim-enhancing
multicystic tumor component ([Fig. 2]). Dynamic susceptibility contrast (DSC) MR perfusion imaging demonstrated low lesional
cerebral blood flow and blood volume ([Fig. 3]). Single-voxel MR spectroscopy demonstrated a lone large N-acetyl L-aspartate (NAA)
peak within a dominant, apparently proteinaceous cystic component, with no significant
choline or creatine peaks ([Fig. 4]).
Fig. 1 Noncontrast axial computed tomography demonstrating a multiloculated lesion in the
left cerebellopontine angle with punctate intralesional calcification (black arrow)
and at least two small foci of fat at the periphery of the cysts (arrowheads).
Fig. 2 (a, b) Coronal constructive interference in steady state (CISS) magnetic resonance
imaging (MRI) demonstrating expansion of the left internal auditory canal, vestibule,
semicircular canals (*) and cochlea (curved arrow). (c) Axial T1-weighted MRI without
contrast demonstrating intralesional fat (arrowhead) and rim-enhancing, internally
complex cystic components, with a more solid or microcystic appearance in the expanded
labyrinthine structures.
Fig. 3 Dynamic susceptibility contrast magnetic resonance (MR) perfusion imaging demonstrating
low lesional cerebral blood flow and cerebral blood volume.
Fig. 4 Single-voxel magnetic resonance (MR) spectroscopy demonstrating a lone N-acetyl L-aspartate
(NAA) peak in the dominant, proteinaceous-appearing, cystic component.
Operation
The patient was placed in the supine position and her head was rotated toward the
right shoulder. A “C”-shaped retroauricular incision was made. The skin flap was rotated
anteriorly, and transection of the external auditory canal was performed. Immediately
upon drilling the outer cortex of the mastoid portion of the temporal bone, tumor
was encountered. A formal mastoidectomy was completed, although the tumor had skeletonized
most of the soft tissue structures of the temporal bone. Stimulation of the labyrinthine
and mastoid segments of the facial nerve was not successful even at 1.0 mA. Tumor
was easily removed from the petrous portion of the internal carotid artery and the
internal auditory canal. After removal of the tumor within the extradural temporal
bone, the presigmoid dura was widely opened, and the posterior fossa contents were
exposed. Two large cysts were incised and drained, which promoted relaxation of the
adjacent neural structures. The remainder of the intradural tumor was solid.
The facial nerve was identified at the level of the brainstem and stimulation was
absent at 1.0 mA. The seventh nerve was intimately involved with the tumor at the
level of the porus acusticus, such that gross total resection without sacrifice seemed
unlikely. As stimulation of the facial nerve was unsuccessful, the decision was made
to transect the nerve. The tumor was somewhat adherent to the brainstem, but was successfully
removed from it. Superiorly, the fifth nerve was associated with the tumor but was
successfully dissected off the capsule. The sixth nerve was visualized medially and
remained intact under a layer of arachnoid. The lower cranial nerves were visualized
inferiorly. Intraoperative examination indicated that a gross total resection was
achieved. The expanded cochlea was not thought to represent neoplasm. Adipose tissue
was inserted into the eustachian tube to prevent leakage of CSF. Adipose tissue was
also placed within the temporal bone defect, and the posterior aspect of the temporalis
muscle was mobilized and placed over fat.
Pathology
The lesion consisted of a complex and disorganized mixture of mature cartilage, bone,
fat, smooth muscle, collagenous connective tissue, and various kinds of epithelial-lined
glands and small cysts. There was a separate fragment of keratinous debris. There
was no evidence of immature or malignant components. These findings were consistent
with a mature teratoma.
Postoperative Imaging
Postoperative imaging demonstrated resection of all intracranial lesional components,
residual deformity of the left fifth cranial nerve cisternal segment, resolution of
mass effect on the cerebellum and brainstem, and stable signal abnormality within
the residual expanded cochlea ([Fig. 5]). Follow-up MR imaging 24 months later demonstrated these findings to be stable.
Fig. 5 Postoperative follow-up axial (a) and coronal (b) coronal constructive interference
in steady state (CISS) magnetic resonance (MR) images demonstrating complete resection
of the intracranial tumor components with stable signal abnormality in the residual
expanded cochlea (curved arrow). Mass effect on the brainstem, cerebellum, and fifth
cranial nerve has resolved.
Postoperative Course
The patient's neurologic examination remained stable with the exception of the expected
complete facial paralysis. She remained in the hospital for 4 days and was discharged
home. Prior to discharge, she received implantation of a gold weight in the left eyelid
to promote closure. The patient did experience an episode of aseptic meningitis that
responded to the administration of steroids. She returned 3 months after the operation
and underwent a hypoglossal-to-facial nerve anastomosis. At her 1-year follow-up,
her facial function had improved to a House-Brackmann grade V/VI facial palsy.
Discussion
Intracranial germ cell tumors can generally be divided into two categories: germinomas
and tumors derived from totipotential germ cells (also called nongerminomatous germ
cell tumors). Nongerminomatous germ cell tumors have a wide spectrum of differentiation,
with teratomas representing the most differentiated of these tumors. Mature teratomas
contain fully differentiated tissue from all three primary germinal layers. Intracranial
germ cell tumors represent 7% of intracranial tumors in the West and up to 15% in
Japan.[4]
[5] Mature teratomas comprise 18 to 20% of germ cell tumors.[4] Most occur in the midline or paramidline locations, such as the pineal region and
sellar/suprasellar area. Lateral locations for intracranial teratomas are exceptional.
There have been cases reported of teratomas involving the ventricular system, Sylvian
fissure, basal ganglia, pituitary fossa, cavernous sinus, middle ear space, petrous
portion of the temporal bone, and middle cranial fossa.[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13] To our knowledge, this is the first case report of an intracranial teratoma involving
the temporal bone with extension into the cerebellopontine angle. Li et al[14] recently published their case of a 4-year-old girl who presented with fevers, headache,
and purulent drainage from her ear. Imaging revealed a 4-cm lesion occupying the middle
fossa with erosion of the petrous bone. Complete resection was achieved with an infratemporal
epidural approach.
Pediatric intracranial germ cell tumors present at an average patient age of 10 to
12 years with variable presentations depending on location.[1] Despite the unusual location in this case, foci of lesional calcification and fat
on imaging are highly suggestive of the diagnosis, as in mature teratomas elsewhere
in the body. As expected for a benign hypovascular tumor, the tumor was hypoperfused
at MR perfusion imaging. Interestingly, NAA, though not generally found in high concentration
outside brain tissues, was elevated in a proteinaceous-appearing cystic lesional component
in this case and has also been found to be elevated in the cysts of serous ovarian
tumors.[15]
Resection of teratomas is necessary to prevent malignant transformation[16] and to obtain enough tissue to confirm the diagnosis because it is not uncommon
for germ cell tumors to have mixed pathology. Complete microsurgical resection is
the only curative treatment for pure teratomas. In the series by Matsutani et al,[5] more than 90% of patients with pure teratomas who underwent a resection survived
at least 10 years. Although chemotherapy and conventional irradiation are effective
forms of treatment for germinoma and nongerminomatous germ cell tumors, they have
no effect on teratomas. Radiosurgery, however, may have a role. Chiu et al[17] described three patients with recurrent mature teratomas treated with marginal doses
of 12 to 17 Gy. Tumor volume reduction ranged from 48% to 89%, with no evidence of
further tumor progression or radiosurgery-related morbidity.
Conclusion
As in our case, when a mature teratoma is known or highly suspected, complete resection
must be the goal and will thus determine the surgical approach. Despite the involvement
of multiple intracranial compartments, all efforts should be undertaken to completely
visualize the lesion to maximize the chance for surgical success. In this case, the
transtemporal corridor provided excellent access to ensure that the utmost removal
of tumor was accomplished.
