Keywords
intraneural ganglion cyst - hypoglossal nerve palsy - hypoglossal canal - transcondylar
approach
Introduction
Most intraneural ganglion cysts present in the peripheral nerves near joints or tendon
sheaths.[1] Cranial nerves are rarely affected. A common location of an intraneural ganglion
cyst is the peroneal nerve behind the fibular head.[2]
[3]
[4] The pathogenesis of ganglion cysts is still unclear but is likely to be developmental.
The cyst can compress and invade the adjacent nerves and become symptomatic.
In the present case a small cyst was confined to the hypoglossal canal, making interpretation
of magnetic resonance imaging (MRI) difficult. This report demonstrates the importance
of an intraneural ganglion cyst as a differential diagnosis in a patient with hypoglossal
nerve palsy.
Case Report
Examination revealed left-sided tongue atrophy and slurred speech. MRI obtained 13
months prior to surgery was initially interpreted as negative, but retrospectively
it showed a nearly imperceptible T2 hyperintense 3-mm lesion related to the hypoglossal
canal ([Fig. 1]). Eight months later, MRI was repeated due to the progression of symptoms. This
MRI revealed a 7-mm T2 lesion with gadolinium enhancement into the left hypoglossal
canal ([Fig. 2]).
Fig. 1 Initial axial T2-weighted magnetic resonance image showing hyperintense legion related
to the hypoglossal canal (indicated by arrow).
Fig. 2 (A) Preoperative coronal T2-weighted magnetic resonance image showing the hyperintense
legion (indicated by the arrow). (B) Axial gadolinium-enhanced T1-weighted image showing
the cystic lesion (indicated by the arrow).
A standard transcondylar extradural approach without transposition of the vertebral
artery allowed evacuation of the cyst, and 360-degree neurolysis of the hypoglossal
nerve was performed to disconnect the cyst from the C0–C1 joint.
The patient had no complications and was discharged on day 2. No recurrence was shown
on MR images obtained 7 months postoperatively. The slurred speech resolved after
a few weeks.
Discussion
We know isolated hypoglossal nerve palsy is rare and most commonly associated with
other cranial nerve involvement.[5]
[6]
[7]
[8] Isolated nerve palsy is reported to be caused by hypoglossal nerve schwannomas,[6]
[7]
[9]
[10]
[11] dural arteriovenous fistulas, enlarged emissary veins of the hypoglossal canal,
aneurysms of the stump of a persistent hypoglossal artery, internal carotid and vertebral
artery dissections, metastatic lesions to the skull base, arachnoid cysts, occipital
condyle fractures, after a neck surgery, or with no apparent cause.[6]
[7]
Many theories have been proposed to explain the pathogenesis of juxtafacet intraneural
ganglion cysts. Although the theories suggest association with a joint,[3] myxoid degeneration and cyst formation in the synovial tissue,[12]
[13] and prior traumatic injury[14]
[15] all may play a role, the origin and pathogenesis of these cystic tumors remain unknown.
To our knowledge, five cases present a patient with an isolated hypoglossal palsy
due to a cranial nerve ganglion cyst.[5]
[7]
[16]
[17] Mujic et al[5] and Elhammady et al[6] classified their cases as atlantooccipital joint synovial cysts. Mujic et al called
it synovial cyst because of the presence of fibrous connective tissue with myxoid
change, and no associated neural tissue was present. Elhammady et al reported a case
of an atlantooccipital juxtafacet cyst that can be classified as a synovial cyst,
lined with synovial cells and containing clear or xanthochromic fluid, or as a ganglion
cyst, which does not have a synovial lining and contains gelatinous content. The other
three cases reported by Baldauf et al,[16] Nonaka et al,[17] and Gambhir et al[7] describe an intraneural ganglion cyst due to the presence of neural tissue affecting
the hypoglossal nerve. The presented case differs by being confined to the hypoglossal
canal.
The present lesion was interpreted as a possible schwannoma, and stereotactic radiosurgery
was offered based on this and the small size of the lesion. Fortunately, the patient
preferred surgery. The lesion was extradural and in the left hypoglossal canal. Given
the location of the lesion, the extradural transcondylar approach was performed. Tumors
at the craniovertebral junction are difficult to remove because of their location
and complex anatomical relations. The transcondylar approach is a versatile approach
to this area and allows access to a variety of intra- and extradural tumors. In this
case, the transcondylar approach allowed complete evacuation of the cyst content and
microneurolysis ([Fig. 3]).
Fig. 3 Intraoperative images. Surgical exploration revealed an intraneural ganglion cyst,
and the transcondylar approach allowed complete evacuation of the cyst content. (A)
Dura (arrow 1) and cyst (arrow 2), below which is concealed the hypoglossal nerve.
(B) Dura (arrow 1), hypoglossal nerve (arrow 2), and gel-like cyst content (arrow
3).
Based on intraoperative findings, the lesion was classified as an intraneural ganglion
cyst of the hypoglossal nerve. The treatment of a cyst is surgical excision.
Conclusion
The extreme rarity of an intraneural ganglion cyst in the hypoglossal canal makes
it challenging to recognize. Due to the favorable prognosis for recovery of muscle
function after surgical decompression, it is important to consider this diagnosis
in cases of intracranial hypoglossal palsy.
