Computer-aided virtual surgery for congenital aural atresia.

HYPOTHESIS: Computer-enhanced three-dimensional (3D) computed tomography (CT) provides accurate spatial representation of the complex surgical anatomy of congenitally atretic ears, and is superior to conventional CT for surgical planning. BACKGROUND: The surgical repair of congenital aural atresia is challenging. Conventional CT, routinely used for surgical planning, is limited in its ability to represent spatial relationships between important structures. Because of the lack of density differences between bony structures in the ear, 3D CT has thus far been useful for representing surface contour but not internal anatomy. METHODS: A two-level segmentation scheme was developed to distinguish structures in the temporal bone. 3D CT reconstructions of congenital ears were produced with a high-resolution helical scanner. An interactive tool was used to mark the ossicles and facial nerve. The segmentation scheme was used to color-enhance the ossicles and otic capsule, and render the surrounding bone translucent. "Virtual surgery" was then performed by subtracting a cylindrical volume of bone lateral to the atresia plate. The enhanced 3D CT reconstructions were correlated with intraoperative video recordings. RESULTS: In four congenital ears, computer-enhanced 3D CT was highly predictive of the actual anatomy. Surgery was avoided in two anatomically unfavorable cases. CONCLUSION: Computer-enhanced 3D CT is a major advance over conventional CT for demonstrating the complex spatial relationships in congenitally atretic ears.

Histologic changes after semicircular canal occlusion in guinea pigs.

HYPOTHESIS: Histologic changes occurring after varying degrees of surgical trauma to the inner ear in guinea pigs can reveal the mechanism of hearing preservation/loss. BACKGROUND: Surgical approaches to the inner ear that allow for hearing preservation have gained increasing acceptance in neurotologic surgery. The mechanisms responsible for hearing preservation and hearing loss after partial labyrinthectomy are as yet poorly understood. METHODS: Ten animals underwent semicircular canal occlusion, suctioning of perilymph, ampullectomy, or wide vestibulotomy. Tone-burst auditory brain stem response (ABR) thresholds were performed at weekly intervals after surgery. After 4 weeks, temporal bone specimens were processed to obtain 10-jim sections from plastic-embedded ears. The histologic findings were correlated with the initial and final ABR thresholds. RESULTS: After surgical occlusion of one or more semicircular canals, ABR thresholds were preserved, as the authors reported previously. Suctioning of inner ear fluid led to transient loss of thresholds with recovery. Ampullectomy produced dichotomous results, with some subjects preserving auditory function and others losing auditory function. Wide vestibulotomy resulted in permanent loss of auditory function in most cases. Histologically, there was intraluminal fibrosis and inflammation near the site of surgical entry. Most specimens showed normal cochlear architecture and hair cell counts, irrespective of the degree of hearing loss. Vestibular hair cells were also well preserved, even when they were close to the site of surgical injury. CONCLUSIONS: These findings suggest that electromechanical changes, rather than cell death, are responsible for changes in auditory and vestibular function after partial labyrinthectomy.

Partial labyrinthectomy with hearing preservation: frequency-specific data using tone-burst auditory brain stem response.

Surgical approaches to the inner ear with hearing preservation have valuable implications for neurotologic surgery. In a previous study in guinea pigs, we demonstrated that click-evoked auditory brain stem responses (ABRs) were preserved after transection and plugging of 1 or more semicircular canals but were lost after entering the vestibule (Smouha EE, et al. Otolaryngol Head Neck Surg 1996; 114:777-784). A limitation of that study was that click-evoked ABR might not represent the function of the entire cochlea. In this study we used tone-burst ABR to determine thresholds across a broad range of frequencies (2 to 24 kHz) before and after surgical entry into the labyrinth at the lateral semicircular canal, ampulla, and vestibule. Serial measurements were made, and a sham surgery group was used as a control. The results obtained with tone-burst ABR generally agreed with those previously obtained with click stimuli. Toneburst ABR thresholds were similar across most frequencies tested. Transection of the lateral semicircular canal resulted in preservation of ABR thresholds. Ampullectomy had a variable effect on ABR thresholds. Vestibulotomy usually resulted in substantial hearing loss. We conclude that hearing can be preserved across a range of frequencies after selective surgery of the inner ear. Surgical entry into the membranous labyrinth near the vestibule is the critical factor contributing to hearing loss after partial labyrinthectomy.

Image-guided surgery of the skull base using a novel miniature position sensor.

Image-guided navigational systems have been a useful adjunct for minimally invasive surgery of the skull base. A novel miniature position sensor has been developed that uses a low magnetic field for real-time tracking of surgical instruments. The 1.7-mm-diameter sensor attached to the position and orientation system (Magellan(R), Biosense, Inc., Johnson and Johnson Co., Baldwin Park, CA) was deployed through various surgical instruments or used in a hand-held fashion with a malleable shaft probe. We report on our experience using this electromagnetic system in a series of lesions of the sella and clivus. After patient/image registration, the system was consistently accurate to within 2 mm. We have found this system to be particularly advantageous in endoscopic surgery of cystic lesions of the skull base, where access is limited and anatomy may be distorted. In three patients, this device obviated the need for an extensive external surgical approach. Case histories are presented, which illustrate the specific advantages this miniature system provides during skull base surgery.

Facial nerve palsy in Lyme disease: evaluation of clinical diagnostic criteria.

OBJECTIVE: Lyme disease must be included in the differential diagnosis of acute facial paralysis in endemic areas. When facial nerve palsy occurs as an isolated finding, the diagnosis of Lyme disease may not be readily apparent. The goal of the present study was to evaluate the frequency with which Lyme disease could be diagnosed based on clinical symptoms alone. STUDY DESIGN AND SETTING: This was a retrospective chart review conducted at a tertiary hospital on Long Island, New York, an area endemic for Lyme disease. PATIENTS: The study population was composed of 50 patients with facial nerve palsy who were seropositive for Lyme disease (or had Lyme disease otherwise clinically proven). MAIN OUTCOME MEASURES: Clinical data were initially used to classify patients as having definite, probable, or possible Lyme disease, using the surveillance criteria of the Centers for Disease Control and Prevention. RESULTS: In the majority of cases, the diagnosis of Lyme disease could not be made from clinical data alone. Specific findings, such as erythema migrans and meningoencephalitis, occurred only inconsistently, and serologic or cerebrospinal fluid tests were usually necessary to establish the diagnosis. Intrathecal antibody production was found in a high proportion of patients. CONCLUSIONS: In endemic areas, Lyme disease should be suspected as a cause of acute facial nerve palsy even in the absence of other clinical symptoms. Cerebrospinal fluid serology is helpful in confirming the diagnosis and planning therapy. Central nervous system infection may be common in Lyme disease facial nerve palsy.

Time course of recovery after Epley maneuvers for benign paroxysmal positional vertigo.

The canalith repositioning maneuver (CRP) of Epley is an effective treatment for benign paroxysmal positional vertigo (BPPV). While CRP has been advocated by some as a "single treatment" for BPPV, others have had less uniform results for this self-limited disorder. In order to better define the role of CRP in relieving vertigo, we studied the time course of recovery in 27 consecutive cases of BPPV. We recorded nystagmus after each head maneuver and at each evaluation until complete resolution took place, using absence of nystagmus as a strict criterion for cure. We found that while 93% of patients improved, many had persistent nystagmus at the first evaluation, and in only 63% was resolution clearly related to a CRP session. We believe that in certain cases, the effect of CRP may be due to adaptive conditioning, rather than particle redistribution.

Partial labyrinthectomy with hearing preservation: an experimental study in guinea pigs.

Recent advances in neurotologic surgery have challenged the traditional belief that violating the labyrinth is incompatible with hearing. Our aim in this study was to define the conditions that result in hearing preservation and hearing loss after surgery on the labyrinth. A guinea pig model was developed. Click-evoked auditory brain stem responses were used to determine hearing thresholds. Animals underwent surgical destruction of part or all of the vestibular labyrinth. Transection and plugging of the lateral semicircular canal resulted in normal hearing. Transection of multiple semicircular canals also resulted in hearing preservation. Intentional suctioning of perilymph from a transected canal led to transient hearing loss with complete recovery. Sequential destruction of the entire lateral semicircular canal resulted in preserved hearing as long as the vestibule was not opened. Wide vestibulotomy resulted in hearing loss. Preliminary histologic studies showed that cochlear hair cells were preserved in most cases. The results of our experiments demonstrate the feasibility of preservation of hearing after partial labyrinthectomy and provide physiologic criteria for developing new operations on the inner ear in human subjects.

Atypical forms of paroxysmal positional nystagmus.

Benign paroxysmal positional vertigo (BPPV) is a common cause of vertigo, and has a typical constellation of physical findings. Atypical forms of paroxysmal positional nystagmus (APPN) also exist, and are thought to represent conditions which are in fact not "benign". We studied 100 consecutive patients with positional vertigo in order to learn whether APPN differed from classic BPPV in etiology or clinical fate, and to learn the incidence of central nervous system (CNS) disorders in these patients. APPN was present in 38% of these patients with diverse causes. One-fourth had CNS disorders or vascular insufficiency, the remainder, otogenic or idiopathic. APPN was more likely than BPPV to have a prolonged (persistent or recurring) clinical course. Although most cases eventually resolved, duration of symptoms tended to be longer, regardless of etiology. We conclude that APPN has a less favorable prognosis than typical BPPV, and that a CNS etiology should be suspected in prolonged cases.

Non-osteitic complications of therapeutic radiation to the temporal bone.

The temporal bone often falls within the field of radiation for head and neck tumors. Whereas osteoradionecrosis is well recognized as the end-stage complication of radiation to the temporal bone, serious non-osteitic complications can also occur, and these are important because the ear is an organ of special sense. Radiation causes changes in the specialized tissues of the ear that can impair function and influence therapeutic decisions. The purpose of this article is to review the non-osteitic effects of radiation on the ear. A series of cases is presented that illustrate the spectrum of non-osteitic complications of radiation therapy. External canal stenosis, otitis media with effusion, chronic suppurative otitis media with or without cholesteatoma, sensorineural hearing loss, vestibular impairment, and facial nerve paralysis are described. Management should be guided by an understanding of the pathogenesis of these complications. The authors believe that non-osteitic complications of therapeutic radiation to the temporal bone are relatively common and warrant increased recognition.

Modern presentations of Bezold's abscess.

The use of antibiotics in suppurative otitis media has greatly diminished the incidence of complications. Deep neck abscess arising from acute mastoiditis, a disease thoroughly described by Frederick Bezold early in this century, has become rare. In the last three years we have treated five cases of deep neck abscess of otogenic origin at our hospital. These cases exemplify Bezold's classic description in their site of origin in the mastoid process and route of spread in the neck. However, our contemporary examples differed in clinical setting, latency of onset, and bacterial cause. In four of the cases, delay in diagnosis occurred because of failure to recognize the disorder. Computed tomography has proved valuable in the anatomic diagnosis and surgical planning. Renewed familiarity with the clinical presentations and pathogenesis of this now uncommon condition may prevent delay in diagnosis and initiation of therapy.

Routine intraoperative facial nerve monitoring during otologic surgery.

We have used intraoperative monitoring and stimulation of facial nerve function routinely in 301 consecutive otologic and neurotologic cases. The device has been safe, simple to use, and practical. Facial contraction is detected by a strain-gauge sensor in the corner of the mouth and is signalled audibly to the surgeon. Electrical stimulation of the facial nerve can be delivered through a sterile probe, which produces a constant-current-square-wave impulse. The device has several advantages: it signals unintentional mechanical stimulation of the facial nerve during surgery; it allows mapping of the nerve through soft tissue, tumor, and bone; it predicts dehiscences in the bony covering of the nerve; and it allows confirmation of the electrical integrity of the nerve before and after surgery. In this paper we present a technical description of the device, relevant intraoperative electrical measurements, and illustrative case examples. Although the device does not replace anatomic knowledge and surgical ability, it provides a margin of security during ear surgery. This system for intraoperative facial monitoring is practical, and the authors encourage its routine use.

Retrosigmoid-internal auditory canal approach vs. retrolabyrinthine approach for vestibular neurectomy.

A new procedure, the retrosigmoid-internal auditory canal (RSG-IAC) vestibular neurectomy, has been developed, presented, and compared with the retrolabyrinthine vestibular neurectomy (RVN). The RSG-IAC involves a 3 cm retrosigmoid craniotomy removal of the posterior wall of the internal auditory canal (IAC) to the singular canal, with transection of the superior vestibular nerve and the posterior ampullary nerve. This effects a complete denervation of the vestibular labyrinth and preserves the patient's hearing. All 11 patients with Meniere's disease were cured of vertigo. Hearing was preserved to within 10 dB of the preoperative pure-tone average (PTA) in 9 of 11 cases. There were no serious complications and no cases of facial paralysis or total hearing loss. The major postoperative problem is persistent headache that necessitates medication. These results compare favorably with--and may be better than those noted after--the RVN procedure. The RSG-IAC vestibular neurectomy is an important improvement in the evolution of vestibular neurectomy for the treatment of vertigo. A prospective study is now in progress to determine which procedure--the RSG-IAC or RVN--best fulfills the goals of vestibular neurectomy.

Fibrous dysplasia involving the temporal bone: report of three new cases.

Monostotic fibrous dysplasia, an unusual disease that can involve the temporal bone, will frequently cause an acquired stenosis of the external auditory canal. Three patients with this disorder who presented with occluded canals are described. Two individuals developed external canal cholesteatomas medial to the obstruction, one of whom eventually developed a postauricular abscess and infected draining sinus. The third patient presented with a restenosis nine months following canalplasty. The cases reported illustrate three surgical criteria necessary to manage these unusual cases successfully: removal of sufficient diseased bone to create a patulous canal; resurfacing denuded bony areas with thin split-thickness skin grafts to prevent soft tissue contractions; an adequate meatoplasty. Postoperatively, the reconstructed canals have remained patent and stable during follow-up periods ranging from one to four years. Clinical, radiographic, and pathologic features of fibrous dysplasia are discussed, the differential diagnosis is presented, and the relevant literature is reviewed.