Surgical Anatomy of the Rat Middle Ear

LEnERS TO THE EDITOR Ciprofloxacin Use in Children To the Editor: Two important issues not included or acknowledged in the study "Effects of Topical Preparations on Hearing in Chronic Otitis Media," by ()zagar et al. (1997;117:405-8), include the effect of round window permeability on diffusion of topical antibiotics and the contraindication (in the United States) of ciprofloxacin use in patients younger than 18 years. Patients included in this study ranged in age from 8 to 62 years. Otitis media is a continuum of disease. Inflammation increases the thickness of the round window membrane while decreasing permeability, thereby protecting the inner ear from ototoxic topical drops.l Middle ear histologic comparison between both treatment arms would have enhanced the study's validity. Unless defined in the drug's package insert, off-label use of a medication places the treating physician in a stand-alone position. Ciprofloxacin should be used in children with this cautionary note. Michael S. Morris, MD, FACS Director; Washington Otitis Media Center 9715 Medical Center Dr., Suite 315 Rockville, MD 20850 23/8/89887

REFERENCE 1. Goycoolea MV, Paparella MM, Goldberg B, et aI. Permeability of the round window membrane in otitis media. Arch Otolaryngol Head Neck Surg 1980;106:430-3.

or asymptomatic. All of these patients had a hypothalamic hamartoma that was clearly visible on cranial MRI but was asymptomatic in 18 patients (including all 4 with epiglottic abnormalities). Because the hamartomas are most often asymptomatic, it is possible that some or all of the individuals reported by McClay et al. may have these lesions. Because of the rarity of cleft epiglottis and the relatively high frequency of this malformation in PHS, it has been recommended that individuals with insertional polydactyly and cleft epiglottis undergo a complete evaluation for PHS, including cranial MRI.2 L. G. Biesecker National Human Genome Research Institute National Institutes of Health Bethesda, MD 20892 F. Ondrey National Institute on Deafness and Other Communication Disorders National Institutes of Health Bethesda, MD 20892 23/8/90739

REFERENCES 1. Biesecker LG, Graham JM Jr. Syndrome of the month: PallisterHall syndrome. J Med Genet 1996;33:585-9. 2. Biesecker LG, Abbott M, Allen J, et al. Report from the workshop on Pallister-Hall syndrome and related disorders. Am J Med Genet 1996;65:76-81.

Surgical Anatomy of the Rat Middle Ear Pallister-Hall Syndrome To the Editor: We read with interest the case report by McClay et al. (1997;116:129-33) describing the combination of bifid epiglottis and polydactyly as "a new genetic syndrome." We wonder if the findings in the family described might be part of the Pallister-Hall syndrome (PHS), an autosomal dominant disorder that includes polydactyly, bifid epiglottis, and hypothalamic hamartoma. l PHS may explain the findings of polydactyly and bifid epiglottis because the inheritance, malformations, and severity of PHS are completely compatible with the findings in the family described by McClay et al. During the past 7 months we have evaluated 20 individuals with PHS. In our series four patients have been found to have epiglottic clefting, which has been mildly symptomatic

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To the Editor: I read with great interest the article titled "Surgical anatomy of the Rat Middle Ear" by R. F. Judkins and H. Li (1997;117:438-447). The study describes the topographic anatomy of the albino rat middle ear and is designed to aid experimental otologic studies of the rat middle ear. As I and my collaborators have extensively studied this subject for almost 20 years and have a great experience with the rat middle ear for otologic research, I do not agree with some of the statements in the report by Judkins and Li and would like to make the following major comments. The authors introduce their study by stating that a description of the surgical anatomy of the guinea pig has been reported "but that of the rat has not." If the authors had carefully searched the previous literature on this subject, they would have found that our research group described the anatomy of

OtolaryngologyHead and Neck Surgery Volume 119 Number 5

the albino rat middle ear in detail in 1982.1 This publication was followed by a couple of papers focusing on certain aspects of the anatomy of the rat middle ear2-4 and how to approach the middle ear cavity for various experiments in order to mimic pathologic conditions of the human middle ear. 5,6 One can argue that some of these articles were published in basic science journals, but they have more recently been referred to in approximately 50 papers from our group in otologic journals. It is also worth mentioning that Hebel and Stromberg7 in 1986 published an atlas on the rat anatomy with excellent black-and-white illustrations on the rat ear and the surrounding tissues. In one of our publications 3 we studied the stapedial artery. It became obvious to us that the artery running through the middle ear cavity and passing between the crura of the stapes is a branch of the internal carotid artery, whereas Judkins and Li describe the stapedial artery as the internal carotid artery per se. However, similar to the condition in other rodents, the persisting stapedial artery should be defined as an anastomosing vessel between the internal and the external carotid arteries. The precise description was obtained and verified by microangiographic studies as well as studies of vascular casts in a previous paper (Fig. I in ref. 4). I agree that for an otosurgeon it is tempting to approach the rat middle ear through a retroauricular incision. However, in animals intended to stay alive for various time intervals after experimental middle ear surgery, the retroauricular approach is very difficult. Except for possible damage to the facial nerve, dissection of the soft tissue immediate to the ear canal will in many cases initiate effusion production. For this reason and also because it is a very time-consuming procedure, we already 10 years ago, abandoned this approach for middle ear surgery in the rat and chose the midline incision from a ventral approach. The ventral approach is easy, fast, and safe, and it has been commented on in several publications. 5 ,6 In this manner the bulla tympanica can be opened, the tubal opening can be plugged, and the round window sealed, as well as several other procedures. In fact, a stapedectomy can be performed, which contrasts to the speculation on impossible stapes surgery in these experimental animals made by Judkins and Li. Judkins and Li also compare the rat with the cat and the guinea pig as animal models for middle ear research. I completely agree that the rat model has certain advantages relative to other animal models for research of the human middle ear. One advantage, which is not commented on by Judkins and Li, is that the tympanic membrane can be approached through a regular ear speculum for inspection, insertion of ventilation tubes, and other manipulating procedures. This cannot be performed in, for example, the cat without severing the muscles of the external ear.

LETTERS TO THE EDITOR

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I welcome the increasing interest in the rat as an animal model for middle ear research, but that also demands that scientists and peer reviewers be updated on the previous research that has been performed on the subject.

Sten O. M. Hellstrom, MD, PhD Department of Otorhinolaryngology University Hospital of Umea S-901 85 Umea, Sweden 23/8/90852

REFERENCES 1. Hellstrom S, Saltn B, Stenfors L-E. Anatomy of the rat middle

2. 3. 4. 5. 6. 7.

ear. A study under the dissection microscope. Acta Anat 1982; 112:346-52. Albiin N, Hellstrom S, Stenfors L-E, et al. Middle ear mucosa in rats and humans. Ann Otol Rhmol LaryngoI1986;95(suppI126): 1-15. Albiin N, Hellstrom S, Saltn B, et aI. The stapedial artery in the rat. A microscopical study under normal conditions and in otitis media with effusion. Acta Anat 1983; 115: 134-40. Albiin N, Hellstrom S, Saltn B, et al. The vascular supply of the rat tympanic membrane. Anat Rec 1985;212:17-2. Johansson U, Hellstrom S, Anniko M. Round wmdow membrane in serous and purulent otitis media. Structural study in the rat. Ann Otol Rhinol Laryngol 1993;102:227-35. Magnuson K, Hellstrom S. Early structural changes in the rat tympanic membrane during pneumococcal otitis media. Eur Arch OtorhmolaryngoI1994;251:393-8. Hebel R, Stromberg MW. Anatomy and embryology of the laboratory rat. 1st ed. Worthesee, Germany: BioMed Verlag; 1986.

Authors 'Reply: We thank Dr. Hellstrom for his comments about our article and apologize for some inaccurate statements made in our article. To make corrections, we want to clarify several points. It was very unfortunate that we were not aware of the work done before us by Hellstrom et aI., neither by our own knowledge nor through communications with other people. This is always a potential problem when publishing on a subject that is not one's primary interest. However, such a mistake could have been avoided if we had been more careful in our literature search and not relied on someone to do it for us. When we repeated a search on MEDLINE (1966 to present), using the key words rat and middle ear and anatomy, five papers, including the one published in 1982 by Hellstrom et aI., were found. It is possible that this reference was previously overlooked and was hence not reported to us because no abstract or institutional information is available on MEDLINE. Further, none of the other publications by Hellstrom et al. were found using this strategy. We have reviewed our dissection of middle ear arteries in light of the Hellstrom et al. publications. Our confusing use of internal carotid and stapedial artery was a major mistake. Unlike in the human being, the stapedial (or pterygopalatine) artery remains as a branch from the internal carotid in the