Molecules with dipoles in periodic boundary conditions in a tetragonal cell.

When a system which contains a dipole, and whose dimensionality is less than three, is studied in a code which imposes periodic boundary conditions in all three dimensions, an artificial electric field arises which keeps the potential periodic. This has an impact on the total energy of the system, and on any other attribute which would respond to an electric field. Simple corrections are known for 0D systems embedded in a cubic geometry, and 2D slab systems. This paper shows how the 0D result can be extended to tetragonal geometries, and that for a particular c/a ratio the correction is zero. It also considers an exponential error term absent from the usual consideration of 2D slab geometries, and discusses an empirical form for this.

Airway injury complicating excision of thyroglossal duct cysts.

OBJECTIVES: We report on four cases of thyroglossal duct cyst (TGDC) excision using the Sistrunk procedure (resection of the mid-portion of the hyoid bone in continuity with a thyroglossal duct cyst tract) in which the airway was significantly injured. The patterns of injury, their treatment and outcomes as well as preventative measures are detailed. METHODS: Retrospective analysis of four patients referred to a tertiary medical center after sustaining injury to the cricothyroid membrane and/or thyroid cartilages while undergoing a Sistrunk excision of a TGDC. RESULTS: Three patients were repaired after a delay; one patient was immediately repaired. All four patients required application of cartilage grafts, and all ultimately required tracheotomy. Decannulation was achieved in the four patients after an average of 4.5 months, and none suffered from aspiration. Voice outcomes were poor in 3/4. CONCLUSIONS: The Sistrunk procedure has been advocated for TGDC excision, citing a low recurrence rate. However, if the thyroid cartilage is mistaken for the hyoid bone, significant airway injury occurs. Urgent laryngotracheoplasty is indicated, but poor voice outcomes are anticipated. SIGNIFICANCE: Surgeons employing the Sistrunk procedure to excise TGDC must remain oriented to midline cervical anatomy, particularly as the hyoid my override the thyroid notch in young children, placing the larynx at risk for significant injury.

Arytenoid prolapse as a consequence of cricotracheal resection in children.

Cricotracheal resection (CTR) is a technique introduced comparatively recently for treating severe laryngotracheal stenosis in children. The recognized complications of CTR include recurrent laryngeal nerve damage, anastomotic dehiscence, and restenosis. We describe a further complication of CTR, namely, prolapse of the arytenoid cartilage. The presentation may be late, with symptoms of shortness of breath on exertion and nocturnal stertor with a poor sleep pattern, or the prolapse may be an asymptomatic incidental finding. The diagnosis is performed with flexible nasopharyngoscopy with the patient unanesthetized, or with rigid endoscopy with the patient lightly anesthetized and spontaneously ventilating. The affected arytenoid cartilage is noted to prolapse anteriorly and medially with inspiration, partly obstructing the airway. If treatment is required, endoscopic laser partial arytenoidectomy is effective. In a series of 44 children who underwent CTR, 20 were noted to develop arytenoid prolapse after operation. Twelve were asymptomatic, and 8 required laser arytenoidectomy, 2 of whom now require continuous positive airway pressure for moderate supraglottic collapse.

Cricotracheal resection in children.

OBJECTIVE: To review our experience with cricotracheal resection in a pediatric population. DESIGN: Prospective case review of a cohort of patients undergoing cricotracheal resection. SETTING: Tertiary care pediatric hospital. PATIENTS: Forty-four consecutive patients undergoing cricotracheal resection between January 1, 1993, and December 31, 1998. MAIN OUTCOME MEASURES: Decannulation rates. RESULTS: Thirty-eight (86%) of the 44 children are decannulated. The ultimate decannulation rate was independent of the presenting grade of subglottic stenosis. Fourteen children (100%) had a primary cricotracheal resection; all are decannulated. Twenty-one children had a salvage cricotracheal resection, and 19 (90%) are decannulated. Nine children had an extended cricotracheal resection, of whom 5 (56%) are decannulated. A primary cricotracheal resection was performed on a child on whom no previous open airway procedure had been performed. A salvage cricotracheal resection was performed on a child on whom previous open airway reconstruction had not resulted in an adequate airway. An extended cricotracheal resection was performed on a child on whom the cricotracheal resection was combined with a second procedure, either additional expansion cartilage grafting or an open arytenoid procedure. Most of these children had complex airway pathologic conditions. CONCLUSION: Cricotracheal resection complements standard laryngotracheal reconstruction techniques in a pediatric population.

Primary neurilemoma of the thyroid gland: a case report.

Primary nonepithelial tumors of the thyroid gland are rare. We present the case of a neurilemoma of the right lobe of the thyroid gland in a 20-year-old female patient. The tumor was asymptomatic and measured 2.5 x 1.2 cm in size. Histologic examination was consistent with an Antoni A-type neurilemoma. The tumor was excised without difficulty. Only 12 other cases of neurilemomas of the thyroid gland have been reported in the literature. We discuss the clinical, radiologic, and pathologic findings of this rare tumor.

Laryngotracheal reconstruction and the hidden airway lesion.

OBJECTIVE: Single-stage laryngotracheal reconstruction (SSLTR) is an increasingly common technique to achieve decannulation of patients with laryngotracheal stenosis. In a proportion of cases airway distress on extubation may be attributed to a dynamic second airway lesion not diagnosed before surgery. Our aim is to describe our recent experience with these frustrating patients. METHODS: Between July 1997 and July 1999 we prospectively followed patients who underwent SSLTR and experienced difficulty after extubation owing to an unsuspected second airway lesion. RESULTS: During this 24-month period we performed 80 SSLTRs. In six surgeries performed on five patients, a second airway lesion complicated extubation. In five patients the second lesion was not diagnosed before surgery because there was significant airway stenosis and tracheotomy. The sixth patient was transferred to our care intubated. In all cases the airway surgery for the dominant lesion was technically successful, but revealed a second dynamic lesion. There were three cases of tracheomalacia, two cases of laryngomalacia, and one case of arytenoid prolapse. All patients required intervention. Tracheotomy was required in four patients. CONCLUSIONS: Failure to achieve extubation after SSLTR may be caused by a dynamic second airway lesion that was previously disguised by a more dominant airway lesion. Surgical repair of the dominant lesion will allow manifestation of the dynamic lesion due to the Bernoulli effect. The combination of a tracheotomy and a dominant airway lesion limits airflow and potentially disguises the situation.

Cricotracheal resection as a primary procedure for laryngotracheal stenosis in children.

OBJECTIVE: Cricotracheal resection (CTR) is being increasingly used in the treatment of children with severe laryngotracheal stenosis. In this institution the majority of children are treated with CTR as a salvage procedure having undergone previous unsuccessful laryngotracheal reconstruction (LTR). Selected children have undergone CTR as a primary procedure (without previous LTR). The objective of this study is to examine the outcome for children undergoing cricotracheal resection as a primary procedure for severe laryngotracheal stenosis. METHOD: analysis from prospectively collected database. RESULTS: 17 patients underwent CTR without previous LTR or anterior cricoid split between October 1994 and September 1998. All the patients had grade 3 or 4 stenosis. After a minimum of 1 year follow up 15 children are decannulated. Five children required further surgery to achieve this. Two children still have tracheostomies. Both had extended procedures. One included bilateral arytenoid abduction for bilateral vocal cord paralysis in a patient with quadraparesis following transverse myelitis. The other child, who suffered from multiple congenital anomalies, underwent a concurrent posterior cricoid cartilage graft. Nine patients had good voice post-operatively, five had acceptable voice and three had weak or no voice. CONCLUSION: the early experience for CTR in children as a primary procedure achieved an overall decannulation rate of 88% after 1 year follow up in children with severe laryngotracheal stenosis. Five children required further surgery to achieve this. The voice outcome was variable. CTR is an alternative primary procedure to LTR for severe laryngotracheal stenosis in children. The relative indications for these procedures are discussed.

Subglottic stenosis associated with transesophageal echocardiography.

Transesophageal echocardiography (TEE) is used extensively to assess cardiac function and anatomical relationships in both adults and children. Although considered a noninvasive procedure, TEE in infants and small children may result in airway complications. A patient who developed subglottic stenosis after the use of TEE during a cardiac procedure is reported.

Gustatory sweating syndrome of the submandibular gland.

Gustatory sweating syndrome involving the submandibular gland is rare. We present a case of a patient who experienced this syndrome 5 years after undergoing submandibular gland resection. Our patient was satisfied simply with an explanation of the disorder and reassurance. But in cases where further intervention is sought, medical and surgical options are available and should be individualized for the patient.

Pediatric type I thyroplasty: an evolving procedure.

The treatment of vocal fold paralysis by type I thyroplasty in the pediatric age group has not been reported. From 1990 to 1998, 12 type I thyroplasty procedures were performed on 8 patients between 2 and 17 years of age. The most common cause of vocal fold paralysis was neurologic, followed by vagal injury from a cardiac procedure. The most common indications for the procedure were aspiration and dysphonia. In our early thyroplasty experience, adult techniques and measurements adapted after Isshiki or Netterville were used. Postoperative laryngoscopy showed that in most cases, the placement of the implant was too high. There were variable outcomes in aspiration and dysphonia with this technique. These findings appear to be independent of thyroplasty approach or of implant design type. We conclude that the standard approach for vocal fold medialization in the adult cannot be applied accurately in the pediatric population. In performing pediatric thyroplasty, the anatomically lower position of the vocal fold must be taken into consideration. We have since modified our technique to adjust for accurate identification of the vocal fold line and medialization. The modified approach for vocal fold medialization in the pediatric population is discussed.

Craniofacial resection of anterior skull base tumours: factors contributing to success.

BACKGROUND: A case series of 20 consecutive patients followed for a minimum of 54 months following craniofacial resection of anterior skull base tumours is presented, with the aim of identifying complications and factors influencing survival. METHODS: A retrospective review of a case series of 20 consecutive patients was carried out. RESULTS: Dural invasion was significantly correlated with poorer survival. There was also a tendency for tumour grade and positive resection margins to be associated with poorer outcome. Most local recurrences occurred within 6 months of surgery, with the exception of adenocarcinoma of the ethmoids, in which recurrence occurred up to 36 months postoperatively. A variety of complications were encountered, with a marked decrease in serious complications from midway through the series. CONCLUSIONS: The change in pattern of complications may be indicative of a learning curve, or the discontinuation of the use of lumbar drainage.

Advanced head and neck cancer: proportionally higher in southland than Otago.

AIMS: To compare the proportion of advanced head and neck cancer presenting from Otago and Southland, and to discuss any differences observed. METHOD: Retrospective review of 186 patients resident in Otago and Southland who presented with a head and neck squamous cell carcinoma to the department of otolaryngology, Dunedin Hospital, between 1985-95. RESULTS: Otago patients had advanced disease in 43% of cases, compared to 66% in Southland patients (p = 0.004). Patients from rural Southland areas had advanced disease in 88% of cases. The incidence of cases was not significantly different between Otago and Southland. No difference was seen in local tumour size, however, Southland had a significantly higher rate of lymph node metastases (p = 0.0003). No difference was also seen in age, gender, duration of presenting symptoms, or delay in referral or diagnosis. CONCLUSIONS: Southland had a significantly higher proportion of advanced head and neck cancer than Otago. Significant differences in access to tertiary health care could not be found. The reasons for the differences observed were unclear.