- Department of Neurosurgery, Faculty of Medicine, Saga University, 5-5-1 Nabeshima, Saga, 849-8501, Japan
Department of Neurosurgery, Faculty of Medicine, Saga University, 5-5-1 Nabeshima, Saga, 849-8501, Japan
DOI:10.4103/2152-7806.72581© 2010 Funaki T This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Funaki T, Matsushima T, Masuoka J, Nakahara Y, Takase Y, Kawashima M. Adhesion of rhomboid lip to lower cranial nerves as special consideration in microvascular decompression for hemifacial spasm: Report of two cases. Surg Neurol Int 18-Nov-2010;1:71
How to cite this URL: Funaki T, Matsushima T, Masuoka J, Nakahara Y, Takase Y, Kawashima M. Adhesion of rhomboid lip to lower cranial nerves as special consideration in microvascular decompression for hemifacial spasm: Report of two cases. Surg Neurol Int 18-Nov-2010;1:71. Available from: http://sni.wpengine.com/surgicalint_articles/adhesion-of-rhomboid-lip-to-lower-cranial-nerves-as-special-consideration-in-microvascular-decompression-for-hemifacial-spasm-report-of-two-cases/
BackgroundAlthough the rhomboid lip is a well-known structure constructing the foramen of Luschka, less attention has been directed to the structure for posterior fossa microsurgeries. The authors report two cases of the hemifacial spasm (HFS) with a large rhomboid lip, focusing on the importance of the structure during microvascular decompression.
Case DescriptionA 59-year-old female presenting with left HFS was admitted to our hospital. A preoperative magnetic resonance image demonstrated an offending artery at the root exit zone of the VII nerve. The patient underwent microvascular decompression through the lateral suboccipital approach. The intraoperative findings showed that a large rhomboid lip adhered to the IX and X cranial nerves and prevented the exposure of the root exit zone of the VII cranial nerve. The rhomboid lip was meticulously separated from the cranial nerves so that the choroid plexus of the foramen of Luschka and the rhomboid lip could be safely lifted with a spatula, and the offending artery was successfully detached from the root exit zone. In another case of a 60-year-old male, the rhomboid lip was so large that it needed to be incised before separating it from the lower cranial nerves. In each case, the HFS was resolved following surgery without any new deficits.
ConclusionThe large rhomboid lip adhering to the cranial nerves should be given more attention in the posterior fossa surgeries and should be managed based on the microsurgical anatomy for preventing unexpected lower cranial nerve deficit.
Keywords: Hemifacial spasm, infrafloccular approach, microvascular decompression, rhomboid lip
The choroid plexus protruding from the foramen of Luschka is an important landmark of the root exit zone of the VII cranial nerve during microvascular decompression surgery for hemifacial spasm (HFS).[
A 59-year-old female presenting with left-sided HFS for 2 years was admitted to our hospital. Neurological examinations demonstrated typical HFS; it is characterized by twitching tonic spasm and synkinesis of the facial muscles. There were no other symptoms. The preoperative magnetic resonance (MR) angiogram revealed that the left posterior inferior cerebellar artery (PICA) formed a rostral loop at the level of the internal acoustic meatus [
Radiological data and intraoperative findings of a patient with left HFS (Case 1). (a) A preoperative MR angiogram in posterior view showing the left PICA which forms a rostral loop at the high level (black arrow). (b) A preoperative MR image illustrating the offending vessel of the PICA at the root exit zone of the VII nerve (white arrow). (c) An intraoperative view showing that a large rhomboid lip (1) adheres to the IX (3) and X (4) cranial nerves; (2) indicates the VIII cranial nerves. (d) Another intraoperative view after separating the rhomboid lip from the IX and X cranial nerves illustrating clearly visualized root exit zone of the VII nerve (6) and the offending PICA (5)
Microvascular decompression of the left VII cranial nerve was performed through the lateral suboccipital approach. Auditory brainstem evoked response (ABR) and facial electromyography were used for intraoperative neurophysiological monitoring. The patient was placed in a lateral park bench position and craniotomy was performed below the posterior end of the incisura mastoidea along the medial boarder of the inferior half of the sigmoid sinus. After dural opening, dissection of the arachnoid membrane around the lower cranial nerves was started. When the inferolateral margin of the cerebellum and the flocculus were gently elevated, a large rhomboid lip was found at the dorsal side of the IX and X cranial nerves [
A 60-year-old male presenting with right-sided HFS for 15 years was admitted to our hospital. Neurological examinations demonstrated typical HFS. The preoperative MR angiogram revealed that the right PICA formed a rostral loop at the level of the internal acoustic meatus. MR images revealed that the PICA compressed the root exit zone of the VII cranial nerve [
Radiological data and intraoperative findings of a patient with right HFS (Case 2). (a) A preoperative MR image showing the offending vessel of the PICA at the root exit zone of the VII nerve (white arrow). (b) An intraoperative view showing an extremely large rhomboid lip (1 and black arrowhead) which adheres to the X (2) cranial nerve and obstructs the approach to the root exit zone (note that the rhomboid lip is intentionally incised). (c) An intraoperative view after separating the rhomboid lip from the IX (3) and X cranial nerves, illustrating clearly visualized root exit zone of the VII nerve (5) and the offending PICA (4)
Microvascular decompression of the right VII cranial nerve was performed through the lateral suboccipital approach with the aid of the same intraoperative monitoring as in Case 1. Intradurally, a large rhomboid lip prevented the visual tract for the root exit zone of the VII cranial nerve and adhered to the dorsal side of the IX and X cranial nerves [
Anatomical relationship among lateral recess, foramen of Luschka, and rhomboid lip
The lateral recesses are narrow, curved pouches formed by the union of the roof and the floor of the fourth ventricle. They extend laterally below the cerebellar peduncles and open through the foramina of Luschka into the cerebellopontine angles. The ventral wall of each lateral recess is formed by the floor of the fourth ventricle and the rhomboid lip, which is a sheet-like layer of neural tissue that extends laterally from the floor and unites with the tela choroidea to form a pouch at the outer extremity of the lateral recess [
Microsurgical anatomy of the rhomboid lip and the lateral suboccipital infrafloccular approach. (a) Posterior view of the left lateral recess (tela choroidea is reflected inferiorly by cutting tenia). The rhomboid lip is located at the dorsal side of the lower cranial nerves. (b) A schema of intraoperative view of the lateral suboccipital infrafloccular approach in the left side. The tip of the spatula is placed on the choroid plexus protruding from the foramen of Luschka. (c) A cadaveric specimen demonstrating an operative view of the lateral suboccipital infrafloccular approach in the left side. The rhomboid lip (arrow) is identified at the dorsal side of the IX and X cranial nerves, with the choroid plexus protruding from the foramen of Luschka and attaches to the lower cranial nerves. The lateral recess curves slight rostrally and the foramen of Luschka opens to the rostral direction. Ch., choroid; Fl, flocculus; Lat., lateral; Med., medial; Pl., plexus; Seg., segment; 4V, fourth ventricle
Rhomboid lip as special consideration for hemifacial spasm surgery
The choroid plexus protruding from the foramen of Luschka is an important operative landmark of the root exit zone of the VII cranial nerve during microvascular decompression through the lateral suboccipital approach.[
To our knowledge, adhesion of the large rhomboid lip to the lower cranial nerves has not been mentioned in the literature on microvasular decompression although the situation does not seem uncommon. One of the possible reasons is that surgeons can mistake the rhomboid lip for part of the arachnoid membrane even when the rhomboid lip is large. The rhomboid lip is a slightly thicker and tougher structure than the arachnoid membrane, and usually does not seem as transparent as the arachnoid membrane. It may still be difficult to distinguish between the arachnoid membrane and the rhomboid lip, especially without anatomical knowledge of the rhomboid lip. Another possible reason for the large rhomboid lip, which has not been mentioned, is that the identification of the rhomboid lip might be difficult especially through the lateral route to the root exit zone of the VII cranial nerve. The infrafloccular approach seems suitable for identifying the large rhomboid lip from the anatomical aspect [Figure
This report sheds light on the clinical importance of the rhomboid lip during microvascular decompression. The anatomical knowledge of the rhomboid lip and the adjacent area may facilitate safer exposure of the root exit zone of the VII cranial nerve. Further studies on the anatomical variation of the rhomboid lip in its size or distance to the cranial nerves are needed to reinforce the importance of the structure for microvascular decompression.
We are grateful to Dr. Albert L. Rhoton, Jr., Chairman-Emeritus of the Department of Neurosurgery at the University of Florida, for providing the opportunity of cadaver dissection. We also thank Mrs. Sumiko Matsushima, Mrs. Laura Dickinson, and Mrs. Akiko Soejima for preparing this manuscript.
1. Hitotsumatsu T, Matsushima T, Inoue T. Microvascular decompression for treatment of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia: Three surgical approach variations: Technical note. Neurosurgery. 2003. 53: 1436-41
2. Huh R, Han IB, Moon JY, Chang JW, Chung SS. Microvascular decompression for hemifacial spasm: Analyses of operative complications in 1582 consecutive patients. Surg Neurol. 2008. 69: 153-57
3. Jean WC, Abdel Aziz KM, Keller JT, van Loveren HR. Subtonsillar approach to the foramen of luschka: An anatomic and clinical study. Neurosurgery. 2003. 52: 860-6
4. Matsushima T.editors. Microsurgical anatomy and surgery of the posterior fossa. Tokyo: Scimed Publications; 2006. p.
5. Matsushima T, Inoue T, Suzuki SO, Fujii K, Fukui M, Rhoton AL, Yamaura A.editors. Microsurgical anatomy of the cranial nerves and vessels in the cerebellopontine angle In: Surgical anatomy for microneurosurgery IV. Tokyo: SciMed Publications; 1992. p. 44-55
6. Matsushima T, Rhoton AL, Lenkey C. Microsurgery of the fourth ventricle: Part 1.Microsurgical anatomy. Neurosurgery. 1982. 11: 631-67
7. Matsushima T, Yamaguchi T, Inoue TK, Matsukado K, Fukui M. Recurrent trigeminal neuralgia after microvascular decompression using an interposing technique. Teflon felt adhesion and the sling retraction technique. Acta Neurochir (Wien). 2000. 142: 557-61
8. McLaughlin MR, Jannetta PJ, Clyde BL, Subach BR, Comey CH, Resnick DK. Microvascular decompression of cranial nerves: Lessons learned after 4400 operations. J Neurosurg. 1999. 90: 1-8
9. Mishler ET, Smith PG. Technical aspects of intraoperative monitoring of lower cranial nerve function. Skull Base Surg. 1995. 5: 245-50
10. Rhoton AL. The cerebellopontine angle and posterior fossa cranial nerves by the retrosigmoid approach. Neurosurgery. 2000. 47: S93-129
11. Rhoton AL. Cerebellum and fourth ventricle. Neurosurgery. 2000. 47: S7-27
12. Sindou MP. Microvascular decompression for primary hemifacial spasm. Importance of intraoperative neurophysiological monitoring. Acta Neurochir (Wien). 2005. 147: 1019-26
13. Wilkins RH. Hemifacial spasm: A review. Surg Neurol. 1991. 36: 251-77