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CASE REPORT

A 22-year-old female visited our hospital due to severe left hemifacial spasm. The spasm had developed 5 years ago earlier and worsened with time. It involved the whole left hemiface, including the left platysma muscle. Con-sistent clonic contraction and fine trembling of the left eyelids were obstructing her field of vision; clonic jerk-ing of the left corner of her mouth made eating difficult. Additionally, the patient had Down’s syndrome. She had a protruding tongue and a short, thick neck. Baseline stud-ies revealed suspicious atlanto-occipital instability, sleep apnea, and effusion of the left middle ear. She was taking antipsychotic medications for mood disorders and had a yearlong hidradenitis suppurativa in her axillary sweat glands. She had a height of 153cm and a bodyweight of 89kg. A magnetic resonance angiography showed that the left posterior inferior cerebellar artery was abutted on the left 7th and 8th cranial nerves (Fig. 1).

An MVD was performed in a park-bench position. The exit zone of the 7th nerve was exposed, and the offend-ing artery was found to be pressing the exit area (Fig. 2A). When the vessel was completely detached from the of-fending site with a Teflon felt (Fig. 2B), the lateral spread-ing response (LSR) from the mental branch showed an exaggerated amplitude, as compared to the baseline wave (Fig. 3). The offending vessel was tracked more proxi-mally and detached at the probable pontomedullary sul-cus. As a result of this process, we observed a reduced LSR. The area of decompression did indeed correspond to a region inferior to the 9th nerve’s origin (Fig. 2B). Af-

Unusual Offending Site of Hemifacial Spasm in Down Syndrome

Yong-sook Park, MD, PhD, Shin-Heon Lee, MDDepartment of Neurosurgery, Chung-Ang University Hospital, Seoul, Korea

We report an experience of microvascular decompression for hemifacial spasm in a patient with Down’s syndrome. She was 22 years old with a five-year history of hemifacial spasm. Intraoperatively the offending site was far more proximal to the root exit zone of the 7th nerve, which was reported by some authors as root emerging zone. The area of decompression correspond-ed to a region inferior to the 9th nerve’s origin. Crowded cranial nerves and vessels may have contributed to the development of the hemifacial spasm and the unusual offending site in this patient because of an anatomical characteristic, small posterior fos-sa in Down’s syndrome.

KEY WORDS: Hemifacial spasm · Microvascular decompression surgery · Down syndrome.

INTRODUCTION

Microvascular decompression (MVD) is widely ac-cepted as a treatment option for hemifacial spasms. Dur-ing surgery, the identification of the offending vessels and affected site is critically important to alleviate the neuro-vascular compression. The most commonly known of-fending sites are at the facial root exit zone (REZ)2) and, occasionally, in cistern3)4) or meatal area.6) Morphometri-cal studies of the posterior fossa in hemifacial spasms have reported that narrow cerebellopontine angle cistern or elevation of the petrous bone9)10) could underlie neu-rovascular compression. People with Down’s syndrome are characterized by having small craniums and round faces with flattened occiput, flat bridge of the nose, flat cheekbones, strabismus, and oblique orbits, and often have an external epicanthus that is higher than the internal epi-canthus.1) The Down syndrome population also typically have vertical hypoplasia of the central structures of the cranium, with lowering in the position of sella turcica, and consequential flattening of the cranial base.5) Small posterior fossa and flattening of the cranial base may pro-mote crowding of cranial nerves and surrounding vessels in the posterior fossa. We report an unusual offending site of a hemifacial spasm in a patient with Down’s syndrome.

Received: September 16, 2020 Revision: September 22, 2020Accepted: September 23, 2020 Address for correspondence: Yong-sook Park, MD, PhD, Depart-ment of Neurosurgery, Chung-Ang University Hospital, 102 Heuk-seok-ro, Dongjak-gu, Seoul 06973, KoreaTel: +82-2-6299-1610, Fax: +82-2-6299-2069E-mail: cuttage@cau.ac.kr

ISSN 1738-6217J Kor Soc Ster Func Neurosurg 2020;16(2):65-67

CASE REPORTCopyright © 2020 The Korean Society of Stereotactic and

Functional Neurosurgery

J Kor Soc Ster Func Neurosurg 2020;16(2):65-67

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ter the surgery, the patient suffered from breathing diffi-culty for 4 days, which was believed to result from mac-roglossia, in addition to excessive lower cranial nerve manipulation. Two months after the surgery, she showed about 10% remnant spasm without any newly reported health issues.

DISCUSSION

The REZ is considered synonymous with the Ober-steiner–Redlich zone, or the transition zone between cen-tral and peripheral axonal myelination, that corresponds to the nerve region 2 to 3mm from nerve’s detachment

out of the pons.3) Campos-Benitez and Kaufmann dem-onstrated the proximal part of the facial nerve REZ with an illustration.3) Before detaching from the pons, the facial nerves are significantly adhered to the pontine surface and traverse along it. This attached portion starts with the root emerging from the pontomedullary sulcus. In their analysis of 115 patients who underwent MVD surgery for hemifacial spasms, the location of the primary neuro-vascular compression was found to be the root emerging portion from pontomedullary sulcus in 10%, the attached portion in 64%, the transition zone in 22%, and the cister-nal portion in 3%. Moreover, Bigder and Kaufmann2) demonstrated that areas more proximal to the REZ, that was attached portion or root emerging zone from ponto-medullary sulcus, were a common offending site in the patients with persistent spasm after MVD surgery. Iijima et al.8) called this area, the emerging portion from the brain-stem in the pontomedullary sulcus, the root emerging zone that is composed of central myelin. The authors suggest-ed that this could be the underlying cause of occasional failures of MVD to improve hemifacial spasms. Intraop-eratively, this region can be manipulated by going through the space just above the glossopharyngeal nerve origin from the medulla oblongata and/or through the space be-tween the lower cranial nerve rootlets.8)

Considering these anatomical and clinical reports, dur-ing MVD, surgeons may approach the more proximal area from the REZ toward the pontomedullary junction. In practice, this may be achieved by decompressing the ves-sels beneath the lower cranial nerves or more inferiorly toward the lateral medulla, as outlined in this presenting case.

In Down’s syndrome, in addition to the small posterior

Fig. 2. The operative field that shows the origin of the 7th nerve, and the plausible offending vessel on it. The vessel is then elevated with a surgical instrument (A). Photograph taken after insertion of the decompression material (B). Decompression with ‘a’ aggravated the lat-eral spreading response (LSR) amplitude in the mental area and additional decompression with ‘b’ reduced the amplitude relative to the baseline LSR. ‘b’ area is inferior to the 9th cranial nerves. 7th N: seventh nerve, 8th N; eighth nerve, 9th N; ninth nerve.

A B

Fig. 1. Preoperative magnetic resonance imaging showed a ves-sel abutting on the left 7th and 8th cranial nerve complex.

Yong-sook Park, et al : Unusual Offending Site of Hemifacial Spasm in Down Syndrome

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cranial fossa, cerebellum and pons were reported as small compared to the cerebrum.7) These anatomical character-istics, such as crowded cranial nerves and vessels in the posterior fossa, may have contributed to the development of the severe hemifacial spasm observed in this young adult with Down’s syndrome. Thus, a more thorough de-compression of the offending vessels along with the fa-cial nerves should be considered in cases similar to the one presented here.

CONCLUSION

Here, we show that hemifacial spasm can develop in patients with small posterior fossa, as is observed in Down’s syndrome. Moreover, we illustrate that thorough decompression of the offending vessels along with the facial nerve must be considered in these cases. Finally, intraoperatively, the area proximal to REZ can be manip-ulated around the lower cranial nerves.

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Fig. 3. The lateral spreading response (LSR) during the surgery. From the left side, baseline waves, aggravated amplitude (arrow) during decompression ‘a’ in Fig. 2 and resolved LSR in the mental area (circle) and forehead (circle) after decompression ‘b’ in Fig. 2.