Tracheal Extension Research Articles

Impact of tracheostomy tube modalities on ventilatory mechanics: a bench study

PurposeTracheostomized patients often present with muscle weakness, altered consciousness, or swallowing difficulties. Hence, the literature is scarce regarding the challenging management of tracheostomy weaning. There is a need to strengthen the understanding of respiratory mechanisms with the different tracheostomy tube modalities that compose this weaning pathway. We aimed to evaluate the impact of these modalities on the work of breathing (WOB), total positive end-expiratory pressure (PEEPtot), and tidal volume (VT).MethodsWith a three-dimensional (3D) printed head mimicking human upper airways, we added a tracheal extension, and pierced to allow insertion of a size 7.0 tracheostomy cannula. The whole was connected to an artificial lung. Three lung mechanics were simulated (normal, obstructive and restrictive). We compared five different tracheostomy tube modalities to a control scenario in which the tube was capped and the cuff was deflated.ResultsA marginal difference was observed on the WOB within conditions with a slight increase + 0.004 [95% CI (0.003–0.004); p < 0.001] when the cuff was inflated in the normal and restrictive models and a slight decrease in the obstructive model. The highest PEEPtot that was reached was + 1 cmH2O [95% CI (1–1.1); p < 0.001] with high-flow therapy (HFT) with the cuff inflated in the obstructive model. We observed a statistically significant reduction in VT [up to − 57 mL 95% CI (− 60 to − 54); p < 0.001] when the cuff was inflated, in both the normal and obstructive models.ConclusionsOur results support the use of conditions that involve cuff deflation. Intermediate modalities with the cuff deflated produced similar results than cannula capping.

Congenital laryngo-tracheo-esophageal clefts: updates from a quaternary care pediatric airway unit

PurposeTo review the operative techniques, outcomes, and complications following surgery in pediatric patients with laryngo-tracheo-esophageal clefts (LTEC). We describe a new combined approach to treat long LTECs.MethodsTwenty-five patients underwent surgical repair for LTEC from March 2012 to July 2022 at our hospital. Every patient underwent a diagnostic endoscopy under general anesthesia and spontaneous ventilation to assess the LTEC and synchronous aero-digestive comorbidities/malformations. All patients underwent at least one surveillance endoscopy after the repair at our institution.ResultsThe patients had multiple other malformations, specifically gastro-intestinal, synchronous airway, and cardiac. The cleft distribution according to the modified Benjamin and Inglis classification was type I (n = 5, 20%), type II (n = 6, 24%), type IIIa (n = 8, 32%), type IIIb (n = 4, 16%), and type IVa (n = 2, 8%). The median follow-up was 44.6 months. Five patients (20%) had undergone previous cleft corrective surgery(s). Seven patients (28%) had partial to complete breakdown of the repair, needing additional intervention(s), and two required a combined—open plus endoscopic repair. Preoperatively, most patients (n = 18, 72%) needed a feeding assistance. At latest follow-up, feeding assistance was weaned off in 13 out of 18 patients, which was a 72% improvement. Ten patients (40%) needed ventilation assistance before the surgery. Post-operatively, ventilatory assistance was weaned off in 6 patients, meaning a 60% improvement.ConclusionLTEC are rare malformations, and their management needs precise diagnosis, appropriate surgical planning, and execution, and dedicated post-operative care. Primary and revision repair of long clefts with tracheal extension may require a combined approach.

EP1.15-03 SMARCA4-Deficient Thoracic Malignancies: A Unifying Genetic Aberration Across Tumors of Divergent Differentiation

Mutations in ATPase-dependant chromatin remodelling units are one of the most common genetic alterations observed in human cancer. Germline mutations in SMARCA4 encoding for Brg-1 protein, a subunit of the SWI/SNF chromatin modifier unit, are well recognised as the causative genetic event in rhabdoid tumor predisposition syndromes that occur in infants and young children. In recent years, somatic mutations in SMARCA4 have been increasingly identified in many adult-onset malignancies ranging from well differentiated carcinomas to poorly differentiated high grade sarcomas in a variety of anatomical sites, including thorax. Documentation of such tumors is essential to our understanding of the pathogenesis and possible mechanisms of therapeutic targetting. Case 1: A 60-year-old male smoker presented with chronic emphyema thoracis of non-tubercular etiology which was treated by intercostal drainage. He had repeated episodes of blockade of chest drain over the next 6 months and eventually a thoracic window was surgically created. Five months following thoracotomy, patient presented with a mass growing at the site of the thoracic window. No other masses in the lung parenchyma or mediastinal lymphadenopathy was seen. Patient underwent an excision of the granulation tissue-like mass. Formalin fixed paraffin embedded sections were subject to microscopy and immunohistochemistry for vimentin, CD34, MIC2, p53, SALL4, pan-cytokeratin (AE1/AE3), EMA, p40, TTF-1, cytokeratin-7, Hepar-1, desmin, myogenin, CD31, S100, Melan-A, HMB-45, GATA-3, calretinin, WT1, INI-1, brg-1 and hematolymphoid markers. Case 2: A 58-year old male smoker presented with hemoptysis and cough. On evaluation, an endobronchial mass was identified and was excised. Formalin fixed paraffin embedded sections from excised tumor mass was subject to microscopy and immunohistochemistry for cytokeratin 7, cytokeratin 19, epithelial membrane antigen, chromogranin, synaptophysin, cytokeratin 20, CD117, TTF-1, NUT1, Her2neu, GATA3, p40, S100, INI-1 and brg-1. Case 1: Microscopy revealed a tumor centred in the soft tissue of the chest wall ulcerating the overlying skin. No lung parenchymal involvement was seen. The tumor was arranged in sheets composed of monomorphic large tumor cells with abundant eosinophilic cytoplasm and prominent nucleoli showing frequent mitoses and foci of necrosis. No squamous or glandular differentiation was seen. Tumor cells were only immunopositive for vimentin, CD34, MIC2, p53, and SALL4, very focally immunopositive for CK (AE1/AE3) and showed retained INI-1 protein expression. Brg-1 expression was lost in tumor cells leading to a diagnosis of SMARCA4-deficient thoracic sarcoma. Case 2: Microscopy revealed a high grade tumor arising from the main bronchi with parenchymal and tracheal extension ulcerating the overlying squamous epithelium. Tumor cells were arranged in lobules with peripheral palisading and central necrosis. The tumor cells were large with frequent cytoplasmic clearing and frequent mitoses. Tumor cells were immunopositive for CK-7, CK-19, EMA, CG while were negative for others. INI-1 was retained while brg-1 was lost leading to a diagnosis of SMARCA4-deficient carcinoma. Two independant studies have delineated SMARCA4-deficient thoracic sarcomas and SMARCA4-deficient lung carcinomas as distinct clinicopathological entities. Despite a unifying genetic alteration, these tumors appear to show varied histomorphology and immunoprofiles. Long term follow-up and molecular analysis of such tumors is necessary.

The surgical management of recurrent tracheal schwannoma

A case of a primary tracheal schwannoma refractory to endoscopic treatment in a 54-year-old male is reported. Previous treatment was by endoscopic laser debulking. Computed tomography (CT) 2 months later demonstrated a recurrent tumour involving the anterior tracheal wall with intraluminal tracheal extension. Treatment was successful by limited tracheal resection with primary anastomosis performed 2 weeks following the scan. The histology confirmed a benign neurogenic tumour derived from Schwann cells and clear margins.

Predictive factors and prognosis for recurrent laryngeal nerve invasion in papillary thyroid carcinoma.

BackgroundRecurrent laryngeal nerve (RLN) invasion in papillary thyroid carcinoma (PTC) is one of the main predictors of poor prognosis. The present study investigated the risk factors for RLN invasion in PTC patients.MethodsA total of 3,236 patients who received thyroidectomy due to PTC in Thyroid and Parathyroid Surgery Center of West China Hospital of Sichuan University were reviewed. Demographics and clinical factors, imaging examination (ultrasonography) characteristics, surgical details, postoperative pathological details, recurrence, and postoperative complications were recorded. Univariate and multivariate analyses were used to study the risk factors of RLN invasion, Kaplan–Meier method was performed to compare the outcomes of tumor recurrence.ResultsPatients with RLN invasion had a higher recurrence rate than those in the control group (p<0.001). Multivariate analyses showed that age greater than 45 years (p<0.001), a largest tumor size bigger than 10 mm (p<0.001), clinical lymph node metastasis (cN1) (p<0.001), posterior focus (p<0.001), extrathyroidal extension (p<0.001), esophageal extension (p<0.001), tracheal extension (p<0.001), and preoperative vocal cord paralysis (p<0.001) were independent predictors for RLN invasion.ConclusionPTC patients with RLN invasion have a negative prognosis and a higher recurrence rate. Meticulous operation and careful follow-up of patients with the above factors is recommended.

Evaluation of Tracheobronchial Lesions with Virtual Bronchoscopy; Correlation with Fiber Optic Bronchoscopy

The aim of this study was to compare the diagnostic accuracy of 3-D virtual bronchoscopy (VB) with that of Fiber-optic (FB) bronchoscopy in patients who had symptoms of respiratory disorders. Thirty patients underwent VB examination. Thin section helical computerized tomography (CT) image were obtained. The volumetric data was downloaded to a workstation equipped with software for surface shaded rendering technique to achieve interactive 3-D virtual “fly-through” examinations of the tracheobronchial tree. Comparison was made between the results of 3-D virtual bronchoscopy, along with multiplanar reconstruction examination with the findings of conventional FB. This information was correlated with the surgical and pathological outcome wherever possible. Virtual bronchoscopy was true positive in twenty-four lesions. Further analysis revealed six cases were with strictures due to tracheobronchial tuberculosis or infection, eight were strictures due to carcinoma, five were endoluminal growths or polyps, three cases had nodes compressing the bronchi, one case had carcinoma of esophagus with tracheal extension and one had a congenital stricture. Virtual bronchoscopy was found false positive in one case, in which a polyp was misdiagnosed. Two endoluminal growths/ polyps were not appreciated on virtual bronchoscopy due to their small size and mild mucosal irregularity. Sensitivity, specificity, positive and negative predictive values were 96%, 50%, 92% and 66% respectively. To conclude VB represents a noninvasive method for evaluating helical CT findings. Further trials with larger sample size are needed on patient populations with any respiratory tract pathology, who do not have any gross findings on conventional examinations and are thus indicated for conventional bronchoscopy.

Results and Survival of Locally Advanced AJCC 7th Edition T4a Laryngeal Squamous Cell Carcinoma Treated with Primary Total Laryngectomy and Postoperative Radiotherapy.

The objective of this study was to analyze the results and survival of patients with T4a laryngeal squamous cell carcinoma (SCC) treated, according to clinical practice guidelines, with total laryngectomy and postoperative radiotherapy (TL-PORT) in a large and homogeneous series. Initial staging assessment, treatment details, pathologic features, follow-up, and patterns of recurrence were retrospectively reviewed in a large series of 100 patients treated in our center between 2001 and 2013 for T4a laryngeal SCC with TL-PORT. Two-, 5-, and 10-year overall survival rates were 65, 52.4, and 33.3%, respectively, while 2-, 5-, and 10-year disease-free survival rates were 55, 42.6, and 31.8%, respectively. In addition, 2-, 5-, and 10-year locoregional control rates were 77, 74, and 65.9%, respectively. Central lymph node involvement was associated with pathologic subglottic extension (p=0.01), lysis of the cricoid cartilage (p=0.03), and tracheal extension (p=0.02). Extracapsular spread of central lymph node metastases, the main prognostic factor identified by multivariate analysis, was associated with decreased locoregional control and survival rates. In this homogenously treated cohort, with consistent guideline application, surgery for T4a larynx cancer remains a standard of care, with current results used as a benchmark.

Primary adenoid cystic carcinoma of trachea presenting as midline neck swelling and mimicking thyroid tumor: A case report and review of literature

We report an extremely rare case of primary adenoid cystic carcinoma (ACC) trachea presenting as midline swelling neck and mimicking thyroid tumor. A 44-year-old female presented with painless midline swelling neck without any respiratory complaints, hoarseness of voice or dysphagia etc. Fine needle aspiration cytology (FNAC) from swelling reveal features of papillary carcinoma thyroid. Subsequently the operative findings, bronchoscopy and histological diagnosis of excised mass, along with review of FNAC, revealed features of ACC of trachea with exra tracheal extension anteriorly into the soft tissue neck, without actual invasion of the thyroid gland. The world literature on extension of an ACC arising in the laryngotracheal complex to thyroid or soft tissue neck and clinical manifestation as a thyroid nodule or mass is reviewed. The cytological differential diagnosis of ACC and CT findings are also briefly discussed.

Metastatic Osteosarcoma

A 25-year-old man presented with increasing shortness of breath and sputum production of 2 weeks' duration. He denied hemoptysis, chest pain, fever, or chills. Examination revealed absent breath sounds over the left hemithorax with stony dullness to percussion. His history was remarkable for osteosarcoma of the right femur 2 years before presentation with subsequent surgical resection and neoadjuvant therapy. A chest x-ray demonstrated total opacification of the left hemithorax. Bronchoscopy was performed demonstrating left main bronchial obstruction secondary to an exophytic, necrotic fungating tumor mass, which was extending proven to be metastatic osteosarcoma by biopsy (Fig. 1).FIGURE 1: Osteosarcoma arising from the left main bronchus and extending into the trachea.Pulmonary metastasis secondary to osteosarcoma is well described; however, luminal spread with endobronchial or endotracheal obstruction is rarely described. DISCUSSION The lungs remain the second most common organs affected by metastatic carcinoma, with 20% to 54% of all patients demonstrating pulmonary metastasis sometime during their disease. Highest propensity for pulmonary metastasis is seen with choriocarcinoma, osteosarcoma, testicular tumors, melanoma, Ewing sarcoma, and Kaposi sarcoma.1 This is the result of the fact that lungs act as the capillary drainage filter for most organs with nonpulmonary neoplasms metastasizing to the lungs through the lymphatic system and pulmonary carcinoma via the hematogenous route.1,2 Despite the frequent metastatic involvement of the lungs, the rate of endobronchial or endotracheal metastasis from nonpulmonary metastasis is variable, with reports ranging from 2% to 50% depending on whether invasion from parenchymal mass or lymph nodes are included.3-5 In Heitmiller et al's review of the Johns Hopkins experience with endobronchial metastasis, they noted that breast carcinoma accounted for 52.2%, renal cell carcinoma in 17.4%, colonic adenocarcinoma in 13%, and carcinoma of the bladder, thyroid, ovary, and nasopharynx in 4.3% each.6 Kiryu et al delineated developmental modes for such metastatic pulmonary involvement: type I with direct metastasis to the bronchus, type II with bronchial invasion by a parenchymal lesion, type III with bronchial invasion by mediastinal or hilar lymph node metastasis, and type IV with peripheral pulmonary lesions extending along the proximal bronchus. Differing developmental modes could have variable median survival times owing to differences in pathogenesis and clinical significance of each mode.3 Osteosarcoma is the most common skeletal malignancy of childhood with metastatic disease to the lungs found in the majority of patients succumbing to this tumor.7,8 Osteosarcoma could also arise in patients with Paget's disease, enchondromatosis, hereditary multiple exostoses, and fibrous dysplasia and most commonly affects the metaphysis of long tubular bones such as the distal femur and proximal tibia.9 On initial workup, approximately 10% to 20% of patients with osteosarcoma will have metastasis with greater than 70% of patients having the lung as the sole site of metastasis.7,10,11 With the introduction of chemotherapy beginning in the 1970s, the 5-year survival rate has improved to 32% to 40% and the incidence of pulmonary metastasis has fallen from 92% to 31%.8 Surgical wedge resection of lung metastasis is potentially curative in 25% to 40% for those patients in whom the primary lesion is under control and complete resection is possible.10,12-15 Significant prognostic factors include the number of nodules, disease-free interval, and resectability of nodules with the presence of 3 nodules or less to be the single most important prognostic factor. Also, if the disease-free interval, described as the time from the primary operation to the date of the first lung recurrence, was greater than 6 months, the median survival increased from 12 to 38 months.16 This patient presented had life-threatening obstruction of the tracheobronchial tree. Patients such as this with unresectable yet symptomatic obstruction for whom regional treatment could improve quality of life are candidates for therapeutic bronchoscopic procedures. Such procedures could include Nd-YAG laser, electrosurgery argon plasma coagulation, or cryotherapy with or without concurrent stent placement.17 The endotracheal extension of this patients mass was noted to have an overlying soft tissue consistency, which was ablated with a combination of Nd-YAG laser and argon plasma coagulation. Mechanical debulking of the calcified component of the tracheal extension was followed by subsequent placement of an expandable metallic stent (Ultraflex; Boston Scientific Co., Boston, MA).

Combined treatment of anaplastic thyroid carcinoma with surgery, chemotherapy, and hyperfractionated accelerated external radiotherapy

To analyze a prospective protocol combining surgery, chemotherapy (CT), and hyperfractionated accelerated radiotherapy (RT) in anaplastic thyroid carcinoma. Thirty anaplastic thyroid carcinoma patients (mean age, 59 years) were treated during 1990-2000. Tumor extended beyond the capsule gland in 26 patients, with tracheal extension in 8. Lymph node metastases were present in 18 patients and lung metastases in 6. Surgery was performed before RT-CT in 20 patients and afterwards in 4. Two cycles of doxorubicin (60 mg/m(2)) and cisplatin (120 mg/m(2)) were delivered before RT and four cycles after RT. RT consisted of two daily fractions of 1.25 Gy, 5 days per week to a total dose of 40 Gy to the cervical lymph node areas and the superior mediastinum. Acute toxicity (World Health Organization criteria) was Grade 3 or 4 pharyngoesophagitis in 10 patients; Grade 4 neutropenia in 21, with infection in 13; and Grade 3 or 4 anemia and thrombopenia in 8 and 4, respectively. At the end of the treatment, a complete local response was observed in 19 patients. With a median follow-up of 45 months (range, 12-78 months), 7 patients were alive in complete remission, of whom 6 had initially received a complete tumor resection. Overall survival rate at 3 years was 27% (95% confidence interval 10-44%) and median survival 10 months. In multivariate analysis, tracheal extension and macroscopic complete tumor resection were significant factors in overall survival. Death was related to local progression in 5% of patients, to distant metastases in 68%, and to both in 27%. Main toxicity was hematologic. High long-term survival was obtained when RT-CT was given after complete surgery. This protocol avoided local tumor progression, and death was mainly caused by distant metastases.

Molecular transformation of recurrent respiratory papillomatosis: viral typing and p53 overexpression.

Recurrent respiratory papillomatosis (RRP) is a histologically benign disease of the larynx, trachea, and bronchi. Here we report on the histologic and molecular characteristics of 7 cases of malignant transformation of RRP to squamous cell carcinoma (SCCA). The clinical histories of 7 patients with RRP who developed SCCA were carefully reviewed. Sequential biopsies were available from 5 of the 7 cases of spontaneous transformation of RRP to SCCA and were reviewed. In addition, p53 protein overexpression and human papillomavirus (HPV) typing for all cases was examined. The average age of patients with juvenile-onset RRP was 3 years, and that of patients with adult-onset RRP was 31 years. The average age of onset of transformation to SCCA was 28 years. All patients had laryngeal involvement with RRP, and 3 of the 7 patients had tracheal extension of disease. Five patients were tracheotomy-dependent. Four of the 7 patients developed SCCA of the lung, while 3 patients developed laryngeal SCCA. There was no consistent histologic progression from squamous papilloma to papilloma with dysplasia, and all but 1 of the SCCAs were well differentiated. The overexpression of p53 protein was variable in each of the 5 patients. We detected HPV types 6/11 in papillomas from 3 patients, and HPV types 6/11, 16/18, and 31/33/51 in a papilloma of a fourth patient. No HPV DNA was detected in papillomas of 2 patients. We found HPV 6/11 in 4 of the carcinomas. We conclude that the spontaneous transformation of RRP to SCCA is not characterized by a histologic progression through dysplasia over time. Transformation can result in the loss of HPV expression. It does not appear that p53 is a molecular marker for monitoring the transformation process. Thus, these cancers may be very difficult to diagnose histologically and clinically early in the course of the transformation of the disease.

Thyroid alar cartilage graft in laryngoplasty: Anatomical study in premature and newborn babies

The aim of this prospective anatomical study was to determine the place of the thyroid alar cartilage graft (TAC) in the laryngotracheoplasty in a population of premature and newborn babies. Ninety-eight fresh larynges, collected from autopsies, were included in the study. After measurement of cartilage dimensions and thickness, the potential dimensions of TAC and its widening capacity were calculated for each specimen. The results showed that TAC thickness was similar to the anterior cricoid arch but was significantly less than the posterior cricoid arch. The maximal degree of stenosis which could be normalized by TAC ranged between 47.8 and 74.3%. The height of the TAC allowed a widening, from the level of the glottis to the inferior part of the second tracheal ring in 100% of cases and to the inferior part of the third tracheal ring in more than 70% of cases. In conclusion, the TAC could be used for anterior grafting in laryngotracheoplasty. Its indications should be limited to grade II and a few grade III of the Myer subglottic stenosis classification without glottic or tracheal extension. Moreover, variability of TAC dimensions leads to peroperatively reassess its indication.

Dynamic features of adherens junctions during Drosophila embryonic epithelial morphogenesis revealed by a Dalpha-catenin-GFP fusion protein.

Cell-cell adherens junctions (AJs), comprised of the cadherin-catenin adhesion system, contribute to cell shape changes and cell movements in epithelial morphogenesis. However, little is known about the dynamic features of AJs in cells of the developing embryo. In this study, we constructed Dalpha-catenin fused with a green fluorescent protein (Dalpha-catenin-GFP), and found that it targeted apically located AJ-based contacts but not other lateral contacts in epithelial cells of living Drosophila embryos. Using time-lapse fluorescence microscopy, we examined the dynamic performance of AJs containing Dalpha-catenin-GFP in epithelial morphogenetic movements. In the ventral ectoderm of stage 11 embryos, concentration and deconcentration of Dalpha-catenin-GFP occurred concomitantly with changes in length of AJ contacts. In the lateral ectoderm of embryos at the same stage, dynamic behaviour of AJs was concerted with division and delamination of sensory organ precursor (SOP) cells. Moreover, changes in patterns of AJ networks during tracheal extension could be followed. Finally, we utilized Dalpha-catenin-GFP to precisely observe the defects in tracheal fusion in shotgun mutants. Thus, the Dalpha-catenin-GFP fusion protein is a helpful tool to simultaneously observe morphogenetic movements and AJ dynamics at high spatio-temporal resolution.

Tracheal involvement in laryngeal papillomatosis.

A review of 39 laryngeal papilloma patients at The Johns Hopkins Hospital revealed an incidence of subglottic and tracheal extension much higher than previously reported. Subglottic disease was present in 69% of patients and tracheal involvement in 26%. Factors associated with distal spread were the presence of subglottic papillomas, history of tracheostomy, total number of endoscopic resections, and the duration of disease. The relationship to the presence of viral antigen was cited. Detection and elimination of all papillomas is felt to be the key for the prevention of distal spread. The strategy of management is described.

Malignant: Surgery for nonanticipated mediastinal and tracheal extension of recurrent laryngeal cancer

Malignant: Surgery for nonanticipated mediastinal and tracheal extension of recurrent laryngeal cancer

Surgery for Unanticipated Mediastinal and Tracheal Extension of Recurrent Laryngeal Cancer

Surgery for Unanticipated Mediastinal and Tracheal Extension of Recurrent Laryngeal Cancer

Tracheal extension in respiration.

It has long been known that the lower end and bifurcation of the trachea are displaced downwards during inspiration. Macklin (1925) described a vertical respiratory displacement of 21 mm. a healthy young adult female. Bruckner (1952), a radiological study, demonstrated an inspiratory descent of the carina of about one thoracic vertebral body young adults of 19 to 25 years of age. Holden and Ardran (1957), a meticulous examination of bronchograms from subjects aged 12 to 65 years, concluded that in deep inspiration the trachea increased length up to one fifth and diameter by about one tenth. In a personal observation, on inspiration the carina descended 30 mm. a young adult male with a full inspiratory movement. Thus, young adults, the carina descends by about 1 in. (2.5 cm.) with deep inspiration, i.e., about 20% of the unextended length of the trachea. There are no references the literature to similar observations infants and young children whom the technical difficulty of securing a full inspiratory and expiratory movement for radiographic investigation is obvious. Also, most observers have examined only the movement of the carina and have not considered changes the whole length of the trachea. Keith (1909) drew attention to the fact that certain parts of the lung are expanded more readily than others. The bases and sterno-costal surfaces related to the more mobile parts of the thoracic wall expand more readily than the apices, mediastinal surfaces, and posterior margins, related to less mobile parts. These areas he described as areas of direct or of indirect expansion. The thoracic wall does not move uniformly during inspiration; the parts which move most are the diaphragmatic and sterno-costal surfaces. Thus the lung tends to expand a downward and forward direction. Now the lung root must obviously descend to facilitate this movement. In

The respiratory horns of Psychoda pupae (Diptera: Psychodidae)

1. The respiratory horn of Psychoda severini Tonn. subsp. parthenogenetica Tonn. is described. Within the tubular horn lies the felt chamber, which meets the horn wall at a number of thin circular regions, the pits, and communicates, through the annulated base of the horn, with the tracheal extension. This has a characteristic retiform thickening and is continuous, at the lower end, with the spiracular chamber, from which a trachea runs to the prothoracic spiracle of the imago.2. At the upper end of the tracheal extension lies the closing mechanism consisting of a lever, and a muscle surrounded by a cuticular sheath. It is suggested that the mechanism functions by compressing the tracheal extension, and that the sheath serves to protect the muscle from the action of the moulting fluid.3. The respiratory horns of fourteen of the British species of Psychoda are described, and it is shown that Ps. spreta Tonn., Ps. albipennis Zett. and Ps. trinodulosa Tonn. are like Ps. severini in possessing long lateral tubes in at least the basal half of the horn, whereas Ps. alternata Say, Ps. surcoufi Tonn., Ps. cinerea Banks, Ps. gemina Eaton, Ps. lobata Tonn., Ps. grisescens Tonn. and Ps. setigera Tonn. have only short lateral tubes. The two species Ps. phalaenoides L. subsp. elongata Tonn. and Ps. crassipenis Tonn. are alike in having a two-branched felt chamber, and Ps. brevicornis Tonn. has a flat triangular horn with a three-branched felt chamber and a cluster of air-containing tubes at each corner.4. An account is given of the development of the respiratory horn of Ps. alternata Say. The horn arises as an outgrowth from the larval prothoracic imaginal disk, and the felt chamber forms by an invagination of its posterior wall. The tracheal extension arises as an invagination of the disk and subsequently acquires a connexion to the felt chamber.5. The development is compared with that of Chaoborus plumicornis, and it is concluded that Weismann's theory of the origin of the horn from two distinct cell layers is not applicable to Psychoda.6. The various terms that have been applied to the respiratory horn are discussed, and the conclusion is reached that though none of them is satisfactory, it is premature to devise a new scheme of nomenclature.Grateful acknowledgements are due to Dr Ll. Lloyd for his help and advice in the course of this work. Some of the material was collected whilst the writer was in receipt of a grant from the Department of Scientific and Industrial Research, to whom acknowledgements are also due.