Saber-Sheath Trachea: Relation to Chronic Obstructive Pulmonary Disease

Transcription

1 Saber-Sheath Trachea: Relation to Chronic Obstructive Pulmonary Disease REGINALD GREENE Downloaded from by on //7 from IP address Copyright ARRS. For personal use only; all rights reserved Sixty male patients with marked coronal narrowing of the Intrathoracic trachea (saber-sheath configuration) were compared with 6 controls. Scores were assigned to patients according to separate clinical and radiographic indexes of chronic obstructive pulmonary disease (COPD). Of the 6 patients with the saber-sheath configuration, 57 (95%) had clinical evidence of COPD compared to only 8% in the control group. Of these 57, 6 (5%) lacked conventional radiographic evidence of COPD. This study establishes a strong correlation between saber-sheath trachea and clinical COPD. The value of this radiographic sign is twofold: () as an aid in diagnosing COPD when other convincing radiographic evidence Is lacking; and () to avoid an erroneous assumption that coronal narrowing is due to a mediastinal mass. The saber-sheath configuration of the intrathoracic trachea is an exceptional static deformity which consists of marked coronal narrowing associated with sagittal widening []. It was first described in a group of elderly men who also had evidence of chronic obstructive pulmonary disease (COPD). In spite of the apparent association between COPD and the saber-sheath tracheal configuration, no certain relation could be established because of the small number of patients previously reported []. The present study compares clinical and radiographic indexes of COPD in 6 patients with sabersheath tracheal configurations and 6 controls. Materials and Methods For this study, the saber-sheath configuration was defined as a trachea with an internal coronal diameter two-thirds or less than the internal sagittal diameter at the same level; cm measurements were made above the level of the aortic arch (fig. ). The degree of saber-sheath shape is expressed as the ratio of the coronal and sagittal diameters (tracheal index). Thus a trachea with a conventional rounded cross section has a tracheal index of one; a trachea with side-to-side narrowing (saber-sheath shape) has an index of less than one; and a trachea with fore and aft narrowing has an index greater than one. All measurements pertain to posteroanterior and left lateral teleoradiographs obtained after maximum inspiration. No instruction was given to the patient to avoid the Valsalva maneuver during the exposure. Patients with saber-sheath tracheas also met the following criteria: () no evidence of mediastinal mass; () extension of the saber-sheath shape the entire length of the intrathoracic trachea; () an abrupt coronal widening of the trachea at the thoracic outlet; and () a tracheal wall thickened with ringlike ossificaton of the cartilages. The study group consisted of the first 6 patients at the Massachusetts General Hospital in whom a saber-sheath tracheal configuration was identified during the period The control group consisted of 6 consecutive male patients 5 years of age or older whose routine elective admission films I interpreted (976). The clinical COPD index for each control and study group patient was obtained by reviewing clinical records and conducting a telephone interview when the record was incomplete. A maximum score of four was possible, with one point given for each of the following: () a positive cigarette smoking history; () an explicit clinical diagnosis of COPD; () a chronic productive cough or explicit diagnosis of chronic bronchitis; and () a clinical diagnosis of COPD confirmed by pulmonary function tests. A score of two or more was considered significant clinical evidence of COPD. A radiographic COPD index was obtained by reviewing the chest radiograph. A five-point score was possible, with one point given for each of the following subjective observations: () depressed diaphragmatic level; () anterior bowing of the sternum; () aerated lung visible beneath the cardiac silhouette on the frontal view; () focal or multifocal pulmonary vascular attenuation; and (5) definite bullous lung disease. A score of two or more was considered significant radiologic evidence of COPD. Results The mean age was slightly greater for the control group than the study group (66. years and 6.9 years, respectively; table ). The mean age difference between the two groups was not significant at the. level (Student s t test). All members of the study group were males; the youngest was 7 years old. A separate listing of the principal clinical diagnoses (i.e., the primary medical diagnosis and/or reason for the radiographic examination) is presented in table. Of the 6 patients with saber-sheath trachea, 8 (%) had principal clinical diagnoses related to the respiratory system : had primary diagnoses of COPD, six had primary diagnoses of lung cancer, and one had pneumonia. None of the control group had principal clinical diagnoses related to the respiratory system. The tracheal configurations of the two groups are significantly different (table ). The coronal diameters are much smaller in the saber-sheath group, and, conversely, the sagittal diameters are much larger than in the control group. The mean tracheal index for the control group (.88) is significantly higher than that of the saber-sheath group (.9). Two patients in the control group had saber-sheath tracheas; both had clinical evidence of COPD. Despite similar body heights and ages in the two groups, the mean tracheal cross-sectional area was significantly smaller in the saber-sheath trachea group than in the control group (6 ± 86 mm SD and 9 ± Received September 6, 977; accepted November 9, 977 Department of Radiology. Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts. Am J Ro.ntgenol :-5, March American Roentgen Ray Society 6-8X/78/ - $.

2 GREENE Downloaded from by on //7 from IP address Copyright ARRS. For personal use only; all rights reserved Fig..-Frontal (A) and lateral (B) radiographs of patient with saber-sheath tracheal configuration and clinical COPD. Arrows indicate supraaortic level at which measurements were made. Note narrow coronal and wide sagittal tracheal diameters (arrows). Coronal diameter on frontal view abruptly widens at thoracic outlet. Anterior bowing of sternum and flattened diaphragm suggest COPD. Bilateral diaphragmatic pleural calcification is result of occupational exposure to asbestos. TABLE Tracheal Configuration and COPD Index Saber-Sheath Trachea Controls Me an ± 5D Range Mean ± 5D Range Age 6.9 ± ± Coronal diameter (mm). ±,9** ±. 5-6 Sagittal diameter (mm) 5.8 ± ±. 8- Trachealindex.9 ±.l** ± Trachealarea(cm) 6 ± ± Clinical COPD index. ±.8** -.9 ±.9 - Radiographic COPD index.... ± 9* -5.5 ±.8 -. significantly different from controls at the.5 level (Student s t test). -. Significantly different from controls at the. level (Student s t test). 67 mm SD, respectively). Although no strong correlation existed between the tracheal cross-sectional areas and either the clinical or radiographic COPD indexes, most of the cross-sectional areas in the control group occurred within the 5-5 mm range. The tracheal cross-sectional area alone, however, does not seem to provide a consistent method for separating the two groups, since many patients with COPD also have crosssectional areas in the 5-5 mm range. The clinical COPD scores of the two groups differed strikingly (table ; fig. ). The mean score for controls was significantly lower than that for the study group (.9 and., respectively). No control patient scored four points and no patient with the saber-sheath configuration scored zero points. Only 8% of the controls but 95% of the saber-sheath trachea patients had COPD (i.e., scored more than one clinical COPD point). The incidence of each element of the clinical COPD index is shown in table. The incidence of smoking was considerably higher in the saber-sheath group than in controls (98% and 65%, respectively). The triad of smoking history, COPD diagnosis and chronic bronchitis was seen in 8% of those with saber-sheath trachea compared to only 8% in controls. The tracheal index correlates with the clinical COPD index (r =.79). A much lower correlation (r =.) is

3 SABER-SHEATH TRACHEA AND COPD Downloaded from by on //7 from IP address Copyright ARRS. For personal use only; all rights reserved Organ System of Principal clinical Diagnosis TABLE Principal Clinical Diagnoses Saber-Sheath No. Trachea % No. Controls Respiratory Cardiovascular Gastrointestinal 9 5 Genitourinary Dermatologic 7 9 Ear, nose, throat Endocrine Neurologic Orthopedic Lymphoproliferative Dental 6 6 Total L.5_JControls, mean LI ssi. mean.tgs 5, - :,:: -... //. - /// I- D #{9}:;o :I LO Clinical COPD Score Fig..-Clinical COPD scores for controls and saber-sheath trachea (SST) group. found when the tracheal index is related to the radiographic COPD index. Like the clinical COPD scores, the mean radiographic COPD scores were significantly higher in the patients with saber-sheath trachea than in the controls (table ; fig. ). Although 95% of the saber-sheath group had clinical indication of COPD, only 55% had a radiographic COPD index greater than one (fig. ). Discussion All 6 patients with saber-sheath deformity reported here are males. Of nearly patients seen with the saber-sheath tracheal configuration, only one female has been encountered. She was 55 years old and had a long history of heavy cigarette smoking as well as clinical and functional evidence of severe COPD and chronic productive cough. Several other women with COPD had tracheal indexes of A much larger study is required to test the relationship between the sabersheath configuration and COPD in females. Thus far, % TABLE Clinical COPD Index Saber-Sheath Trachea Controls No. % No. % Smoking history COPDdiagnosis Chronic bronchitis Abnormal airflow rates.... coo. All patients with chronic bronchitis also had a positive smoking history and diagnosis. 7 Controls; mean.5#{9}o.8 6 :: S S T, mean. 5 - I- #{6} C a V..... Q : _[L! Radiographic COPD Score Fig..-Radiographic COPD scores for controls and saber-sheath trachea (SST) group. saber-sheath configuration is much less common and less pronounced in females with COPD than in males. In 95 the pathologist Simmonds [] described a saber-sheath deformity in cadavers. He regarded it as a condition restricted to old men and called it Alterss#{8}belscheidentrachea (saber-sheath-shaped trachea of old age). He did not recognize that the deformity was limited to the intrathoracic portion of the trachea. Although almost all of the patients in Simmonds s series had emphysema, he did not associate the deformity with obstructive airways disease. The present study indicates that although the saber-sheath deformity does occur in older middle-aged men, it also occurs in young adults with COPD. The youngest patient in this report with saber-sheath trachea and COPD was 7 years old; 7% of the patients with the saber-sheath deformity were less than 5 years of age. In the first radiographic description of saber-sheath trachea, the coincident clinical evidence of COPD in each patient suggested a link between the two. The findings of the present study strongly corroborate that relationship. Of the 6 patients with the saber-sheath deformity, 57 had a clinical diagnosis of COPD. The data further indicate a.8 inverse linear correlation

4 GREENE Downloaded from by on //7 from IP address Copyright ARRS. For personal use only; all rights reserved Fig..-Frontal (A) and lateral (B) radiographs of patient with saber-sheath tracheal configuration and clinical COPD but no convincing conventional radiographic indications of COPD. There is slight anterior bowing of sternum but no diaphragmatic depression in spite of maximum inspiration. between tracheal index and clinical indicators of COPD. Unpublished data from a study relating functional evidence of severe obstructive lung disease to tracheal shape indicate that while the tracheal index in patients with severe COPD exhibits great variation, it tends to be lower than in normal patients. However, many patients with severe COPD do not have the saber-sheath tracheal configuration. The present study, on the other hand, strongly establishes the corollary that COPD is highly likely to be present when the saber-sheath shape is found. Clinical evidence of COPD in every patient with the saber-sheath trachea would not be expected since it is now well known that significant small airways obstruction may be present without clinical evidence of airflow obstruction []. It is interesting to speculate about the incidence of saber-sheath tracheal deformities in patients with COPD and normal chest radiographs. Of the patients in this study with both clinical COPD and saber-sheath trachea, 5% did not have convincing conventional radiographic evidence of COPD. In the study group. identification of the saber-sheath deformity significantly increased the sensitivity of radiographic diagnosis of COPD. Recognition of the saber-sheath shape is also of potential value in avoiding an erroneous assumption that coronal narrowing of the trachea is due to a constricting med iastinal mass. The reduced cross-sectional area of saber-sheath trachea is not likely to be responsible for the clinical signs of COPD or the reduced airflow rates which are generally observed [, 5]. In fact, many patients with severe COPD have tracheas with normal or very large cross-sectional areas. Several mechanisms may potentially be responsible for the development of saber-sheath trachea. Normal young adults and children have approximately circular tracheal cross sections [6]. Although there are no published reports of serial changes in tracheal shape from the circular to the saber-sheath shape in adults, review of earlier films in a few patients in this study showed progressive accentuation of the saber-sheath deformity over several years. Clearly the saber-sheath deformity is not present at birth and must develop during adult life. To my knowledge it has never been seen in infants or children. Fluoroscopy during tidal respiration shows a normal slight increase in the caliber of the saber-sheath trachea during inspiration and a decrease during expiration. but no abnormal tendency toward collapse. The side walls and membranous posterior wall tend to approximate themselves during forced expiration or cough, just as they do under normal circumstances. Postmortem examination of one patient with a saber-sheath trachea and COPD showed no evidence of tracheomalacia []. On the contrary, at autopsy the saber-sheath trachea is found to be somewhat rigid and fixed in shape, and the tracheal rings are densely ossified. As might be expected, the Valsalva maneuver has no effect on the size or shape of the intrathoracic trachea in normal or saber-sheath tracheas, since the increased intraairway pressure is matched by an equivalent increase in extratracheal pressure. The only potential

5 SABER-SHEATH TRACHEA AND COPD 5 Downloaded from by on //7 from IP address Copyright ARRS. For personal use only; all rights reserved cause of narrowing of the intrathoracic trachea during Valsalva maneuver is air compression, which is a minor effect. Limitation of the saber-sheath shape to the intrathoracic portion of the trachea suggests that this extraordinary configuration somehow reflects the action of abnormal intrathoracic forces on it. Chronic bronchitis is exceptionally common in patients with saber-sheath tracheas. It is possible that the cartilaginous ring ossification seen in saber-sheath tracheas is a manifestation of injury secondary to recurrent coughing. The injury can cause cartilaginous degeneration and repair. Cartilage, like bone, has the potential of remodeling itself after degeneration in reaction to injury [7]. Perhaps the saber-sheath shape is an expression of how the injured trachea remodels itself in an abnormally shaped thorax. It is conceivable that the trapped gas volume of upper lobe obstructive lung disease greatly restricts the potential side-to-side dimensions of the paratracheal mediastinum, forcing the trachea to remold itself into a saber-sheath configuration in some patients with COPD. REFERENCES. Greene A, Lechner GL: Saber-sheath trachea: a clinical and functional study of marked coronal narrowing of the intrathoracic trachea. Radiology 5 :65-68, 975. Simmonds M : Uber Alterss#{8}belscheidentracha. Virchows Arch fpathol AnatJ 79 : 5-8, 95. Hogg JC, Macklem PT, Thurlbeck WM: Site and nature of airway obstruction in chronic obstructive lung disease. N Engl J Med 78 :55-6, 968. Lechner G: Form und GrOss der Trachea bei Lungengesunden und bei Patienten mit chronischer obstruktiver Lungenerkrankung. Wien KIm Wochenschr87:l-5, Baum M, Benzer H, Lechner G: Der Einfluss von Trachealstenosen und Rekurrensparese auf den Str#{}mungswiderstand der menschlichen Trachea. Bruns-Beitr KIm Chir :76-86, Engel 5: The Child s Lung. Ann Arbor, Mich., University Microfilms, 959, pp Mankin HJ: The articular cartilages; a review. American Association of Orthopedic Surgeons, Instructional Course Lectures, vol 9, St. Louis, Mosby, 97, pp -