Air in unusual places: Some causes and ramifications of pneumomediastinum

ClinicalRadiology (1982) 33, 301-306

0009-9260/82/00350301502.00

© 1982 Royal College of Radiologists

Air in Unusual Places: Some Causes and Ramifications of Pneumomediastinum A. sCHULMAN, S. F A T A A R , J. W. VAN D E R SPUY*, P. C. G. MORTON and J. H. CROSIER*

Department of Diagnostic Radiology and the *Trauma Unit, Groote Schuur Hospital, and the University of Cape Town, Republic o f South Africa Five unusual cases o f pneumomediastinum are described. In three the probable cause was thoraco-abdominal straining against a closed glottis during violent exercise, in criminal assault, or competitive sport. The resultant increase in intra-alveolar pressure produces an air leak which passes via the pulmonary interstitium into the mediastinum. It can then pass up into the neck to produce widespread subcutaneous emphysema and down through the diaphragmatic hiatuses to produce extraperitoneal emphysema. This m a y outline the lower surface of the diaphragm to simulate intraperitoneal air, b u t it can also leak through the parietal peritoneum to result in actual intraperitoneal air. Therefore, in the patient who has been hospitalised after violent physical stress with or without blunt trauma, pneumomediastinum does not necessarily indicate tracheobronchial or oesophageal rupture and subdiaphragmatic air does n o t necessarily indicate bowel rupture. Probably any form o f exercise in which the Valsalva manoeuvre is performed may cause pneumomediastinum, as m a y other causes 0fincreased intra-alveolar pressure such as mechanical ventilation, bronchospasm, coughing and vomiting. Vomiting is a likely contributing cause in the pneumomediastinum o f diabetic ketosis, o f which a case is described. Another case is presented in which air passed in the opposite direction, from perforated extraperitoneal bowel up into the mediastinum.

The purpose o f this article is to emphasise: (a) Some uncommon causes o f pneumomediastinum for which no specific therapy m a y be required; (b) That air in the mediastinal compartment can pass readily through the diaphragmatic hiatuses into the extraperitoneal compartment and vice versa; (c) That the extraperitonal compartment extends along the undersurface o f the diaphragm so that the presence o f subdiaphragmatic air should not automatically lead one to diagnose intraperitoneal bowel rupture with the necessary corollary o f emergency laparotomy; and (d) That extraperitoneal air can leak into the peritoneal cavity so that even actual intraperitoneal air may not be due to bowel rupture.

CASEREPORTS Case 1. A previously well 17-year-old youth presented in severediabetic ketosis after a few weeks of typical symptoms. He was successfully treated with insulin and intravenous Mdress for reprints: Dr A. Schulman, Department of Radiology, Tygerberg Hospital, Tygerberg, 7505, Republic ~fSouth Africa.

rehydration. On the second day of hospitalisation, mediastinal crunch was heard on auscultation and there was subcutaneous emphysema in the neck. A chest radiograph confirmed pneumomediastinum (Fig. 1), which had cleared on repeat examination 4 days later. He had not indulged in vigorous exercise or been traumatised, and suffered from no respiratory or other diseases except for the diabetes. Case 2. A 17-year-old youth taking part in a surf lifesaving competition collided heavily with another participant and crashed to the sand. He subsequently felt discomfort over the front of the neck with some difficulty in breathing and swallowing, and was admitted to the Trauma Unit. Subcutaneous emphysema was present over the neck, and the chest radiograph showed a small amount of air in the mediastinum (Fig. 2). All these features improved rapidly and he was discharged the following day. Case 3. A 28-year-old man was assaulted while intoxicated. He was admitted to the Trauma Unit in a semicomatose state and with severe widespread bruising. There were scalp and face lacerations but no evidence of penetrating or sharp injury elsewhere. Severe subcutaneous emphysema was present over the thorax and neck. Radiographs showed a great deal of air in the mediastinum as well as around the right kidney and under the right hemidiaphragm (Fig. 3a, b). A small left pneumothorax was also present. There were fractures of the lumbar spinal transverse processes and of the ninth, tenth and eleventh ribs on the left side; the left renal outline was normal however and there was no haematuria. The abdomen felt entirely normal to clinical examination. Radiological examination of the upper gastrointestinal tract showed no leak from oesophagus, stomach or duodenum. Peritoneal lavage showed no evidence of intraperitoneal bleeding. Transcricothyroid bronchography showed an intact

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Fig. 1 - Case 1. Pneumomediastinum in diabetic ketosis (arrows).

Fig. 2 - Case 2. Pneumomediastinum after strenuous sport and blunt trauma (arrows). Subcutaneous emphysema is also present.

tracheobronchial system. Maxillary sinus fracture was considered but excluded by clinical and radiological follow-up. The subcutaneous, mediastinal and extraperiotoneal air collections cleared spontaneously; the left pneumothorax was drained. Management with tracheostomy and mechanical ventilation was instituted but all his abnormal air collections were at their maximum before this was begun. In spite of a period of acute renal failure necessitating peritoneal dialysis, as well as massive rectal haemorrhage for which no cause could be found by endoscopy and gastrointestinal panarteriography, he recovered completely. Case 4. A 30-year-old man was severely assaulted while intoxicated and subsequently admitted to the Trauma Unit. The following day extensive subcutaneous emphysema involving the neck and much of the trunk had appeared. Radiographs revealed air in the mediastinum, under both hemidiaphragms, and a great deal outlining the kidneys and psoas muscles extraperitoneally (Figs. 4a, b). At no stage was pneumothorax present. Repeated clinical and radiographic examinations showed no evidence of fracture or perforation of the facial skeleton or paranasal sinuses, nor was there evidence of sharp or penetrating injury to the chest or abdomen. Because of some generalised abdominal tenderness and because the subdiaphragmatic air was regarded as intraperitoneal, laparotomy for suspected bowel rupture by blunt

trauma was performed. The only abnormal finding however was extensive retroperitoneal and omental emphysema; the duodenum and other parts of the bowel were intact. The patient recovered rapidly and completely with spontaneous disappearance of the abnormally situated air. Case 5. A 21-year-old man presented to the Trauma Unit with severe chest and abdominal pain 36 h after receiving a stab wound in the right flank which had then been sutured. There was tenderness and guarding in the right flank and mediastinal crunch was heard on thoracic auscultation Radiographs showed air around the kidneys, under both hemidiaphragms and in the mediastinum (Fig. 5). At emergency laparotomy, the caecum was found to be retroperl" toneal and the stab had penetrated its posterior aspect. The caecum and ascending colon were mobilised, a tube caeen" stomy was performed and the retroperitoneum drained. Subsequently an extensive retroperitoneal abscess developed but this cleared following further surgical drainage. All the abnormal air collections cleared spontaneously.

DISCUSSION M a c k l i n ( 1 9 3 9 ) s h o w e d in a n i m a l experinae~ts t h a t , w i t h i n c r e a s i n g pressure in t h e airways, air c~

CAUSES O F PNEUMOMEDIASTINUM

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leak from the alveoli into the pulmonary interstitium and pass via the connective tissues of the bronchoarterial and veno-lymphatic bundles into the mediastinum. The mediastinal connective tissue planes communicate freely with those of the neck so that pneumomediastinum readily produces emphysema in the neck and vice versa. From the neck, the subcutaneous compartment is continuous over the whole body so that a substantial amount of air can diffuse very widely as in Cases 3 and 4. The connective tissues traversing the aortic, oesophageal and caval hiatuses of the diaphragm and lining the three gaps around its xiphoid insertions serve as pathways between the mediastinum and the extraperitoneal compartment (Kleinman et al., 1978). Air can pass between the mediastinum and the extraperitoneal tissues in either direction.

Pneumomediastinum may arise from within the mediastinum by oesophageal tears caused by endoscopy or vomiting, or from tracheobronchial tears caused by severe blunt trauma to the upper chest (Harvey-Smith et al., 1980). It may represent air that has tracked downwards from subcutaneous emphysema of the neck arising from fractures of the paranasal sinuses (Tofield, 1977; Adendorff etal., 1977), from tracheal leakage due to intubation, tracheostomy, transcricothyroid bronchography or blunt trauma (O'Neill and Symon, 1979; Eklof and Thomasson, 1980), from dental extraction (Sandler et al., 1975) or from jaw surgery (Piecuch and West, 1979). It may represent air that has tracked upwards from the exterperitoneal tissues due to bowel perforation (our Case 5) (Meyers, 1974; Stahl et al., 1977; Beerman et al., 1981). Lastly, but perhaps most frequently, it can be due to pulmonary alveolar leakage (our Cases 1-4). Conversely, emphysema in the neck or in the extraperitoneal tissues may represent air that has tracked from the mediastinum. Therefore air in any of these sites may indicate a leak from a local or distant hollow viscus. Management will then largely depend upon the clinico-radiological determination of exactly which viscus has leaked and why, and may involve immediate operation and antibiotics, or only reassurance and observation especially if only an alveolar leak has occurred. The extraperitoneal space can be divided into the intercommunicating perirenal, anterior pararenal and posterior pararenal compartments (Meyers, 1976). The latter is circumferential around the abdomen and

(a)

(b)

Fig. 3 - (a) Case 3. Pneumomediastinum lifting off the paravertebral (black arrows) and paracardiac pleura (white arrows) after Violent assault. Subcutaneous emphysema is also present. (b) Case 3. Extraperitonal air under the right hemidiaphragm (straight arrow) and around the kidney (curved arrows).

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(a)

(b)

Fig. 4 - (a) Case 4. Pneumomediastinum (arrows) and subcutaneous emphysema after violent assault. Copious extraperitoneal a~ below the diaphragm (triangles). (b). Case 4. Extmperitoneal air in the flank stripe (arrows) and outlining both kidneys and both psoas muscles. Subcutaneous air coming down from the neck (triangles).

lines the undersurface of the diaphragm. Thus extraperitoneal air may not only outline the kidneys, the psoas muscles and the flank stripes but also the undersurface of the diaphragm (Cases 3 - 5 ) (Turner and Fry, 1977). This last anatomical fact is still over-

Fig. 5 - Case 5. Following a stab wound to the retroperitoneal caecum, there is extraperitoneal air around the kidneys (curved arrows), under the diaphragm (straight black arrows) and in the mediastinum (white arrows).

looked in several recent articles as well as by staff who in dealing with acutely hospitalised patients tend automatically to attribute subdiaphragmatic free air to intraperitoneal bowel rupture. However, even if intraperitoneal air is truly present (as indicated by seeing both sides of the wall of non-adjacent, intra. peritoneal bowel loops) it may simply be incidental to recent laparotomy, peritoneoscopy, peritoneal dialysis, peritoneal aspiration, diaphragmatic dissec. tion in cardiac surgery, external cardiac massage (not always due to bowel rupture) or pneumatosis cystoides intestinalis (Glanz et al., 1978; Atcheson et al., 1975; Wollock et al., 1972). Even more innocently, it may arise from air that has passed up the Fallopian tubes during coitus, douching or tubal insufflation, or during exercises or vaginal examination in the post-partum period (Gantt et al., 1977). To confuse matters further, extraperitoneal air may leak through the parietal peritoneum; thus even if intraperitonal air is truly present, it may only be a ramification of extraperitoneal air and hence of pneumomediastinum (Turner and Fry, 1977). Due to the higher pressures existing in the mediastinum and in the extraperitoneal tissues, air may leak from the mediastinum into the pleural cavity and from the extraperitoneal space into the peritoneal cavity, bu! not vice versa. If the clinical features or the nature 0I any trauma lead one to suspect the possibility of bowel rupture, then water-soluble contrast studies should be done with or without diagnostic peritoneal lavage.

CAUSES OF PNEUMOMEDIASTINUM

pneumothorax and subdiaphragmatic air may coexist as effects of a common cause such as mechanical ventilation. It is impossible however for pneumothorax to produce extraperitoneal or intraperitoneal air unless the diaphragm has been traumatically ruptured (Fataar and Schulman, 1979) or unless the pleuro-peritoneal canals of the embryonic diaphragm (Hamilton and Mossman, 1972)have remained open after birth. Turner and Fry (1977) could find no case report in which these canals could be implicated although we have subsequently come across such a patient (Fataar et aL, 1982). There are a number of situations in which pneumomediastinum and its ramifications can appear through the common mechanism of increased intraalveolar pressure causing interstitial rupture. Positive pressure ventilation can produce it at any age; the high pressures sometimes necessary can rupture the visceral pleura to cause pneumothorax, and can even dissect tile pericardial reflection around the pulmonary veins to cause tension pneumopericardium in the neonate (Mansfield et al., 1973; Rohlfing et al., 1976; Turner and Fry, 1977; Johnston and Altman, 1979; Summers, 1979; Higgins et al., 1979). Vomiting can produce pneumomediastinum by increasing intra-alveolar pressure (Zegal and Miller, 1979), but also more seriously via a Boerhaave tear of the oesophagus. It has been reported in anorexia nervosa, a condition in which self-induced vomiting occurs (A1-Mufty and Bevan, 1977; Donley and Kemple, 1978; Brooks and Martyn, 1979; Chatsfield et al., 1979) and in diabetic keto-acidosis in which vomiting and hyperpnoea occur (Girard et al., 1971; Toomey and Chinnock, 1975; Zahler et aL, 1978). It is an established, though unusual, complication of asthma, presumably due to the expiratory straining and coughing against narrowed bronchi (Richard et al., 1978; Dattwyler et al., 1979). A variety of other bronchopulmonary conditions such as measles (Bakatubia et al., 1978; Yalaburgi, 1980), sarcoidosis (Amorosa et al., 1978), bronchial obstruction, atelectails, pneumonia (Richard et al., 1978), and possibly miliary TB (Narang et al., 1977) can cause it on rare occasions, probably through the machanism of coughing. Prolonged yelling or cheering have also been implicated (McMahon, 1976; Hanzicker et aL, 1977). Thoraco-abdominal straining against a closed glottis increases intra-alveolar pressure and this has been the mechanism blamed for those cases appearing during or shortly after strenuous childbirth or even defaecation (Macklin and Macklin, 1944; Adwers et al., 1974; Brandfass and Martinez, 1976; Richard et al., 1978; Gilstrap et al., 1979). We believe this kind of physical exercise to be the likely cause in our cases 2, 3 and 4 as they were each under the maximal, 21

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combative strain of criminal assault or competitive sport. McMahon (1976) showed that 'spontaneous' pneumomediastinum is not a rarity amongst Marine recruits, and attributed it to their training programme of vigorous exercise with singing and yelling. Lotz et al. (1979) rightly re-emphasised that the bluntly traumatised patient with air in the mediastinum or neck who has not been mechanically ventilated must be a suspect for tracheobronchial rupture. We wish to add as a rider however that if the trauma was accompanied by maximal exercise (as in our Cases 2 - 4 ) then alveolar leakage may be the cause. Macklin and Macklin (1944) even suggest that blunt trauma itself may increase intrathoracic pressure sufficiently to cause alveolar leakage. Air in the mediastinum rarely causes compression because of its ease of escape into the neck. Hypotension and a narrowed trachea have however been reported in a case of tension pneumomediastinum, probably due to mediastinal adhesions; this was relieved by drainage of the mediastinum through an emergency bedside suprasternal incision (yon Stiegmann et al., 1977).

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