98 Alsoub, Chacko

Descending necrotising mediastinitis

Hassam Alsoub, Kadavil C Chacko

Hamad MedicalCorporation, Doha,QatarH AlsoubKC Chacko

Correspondence toH Alsoub, Hamad MedicalCorporation, PO Box 3050,Doha, Qatar

Accepted 29 July 1994

SummaryDescending necrotising mediastinitis is arare but serious complication oforopharyngeal infections with high mor-tality. Diagnosis is frequently delayed,contributing to this high mortality, butawareness of such a complication andearly diagnosis using computed tomo-graphic scanning leads to prompt sur-gical drainage, proper antibiotic therapy,and survival.

Keywords: descending necrotising mediastinitis, CTscanning

Introduction

Acute suppurative mediastinitis is a severeinfectious condition that is most commonly theresult of oesophageal perforation or rupture.Oropharyngeal infections may cause descen-ding necrotising mediastinitis characterised byrapid tissue destruction and high mortalityunless vigorous and effective therapeuticmeasures are taken. Three cases of descendingnecrotising mediastinitis secondary to periton-sillar abscess have been reported previously.Over the last two years we have treated twopatients with descending necrotising medias-tinitis secondary to peritonsillar abscess. Theclinical courses of these two patients are des-cribed and previous publications reviewed.

Case 1A 32-year-old previously healthy man present-ed with a four-day history of sore throat,difficulty in swallowing, and fever. Physicalexamination revealed a pyrexia of 40.8'C,blood pressure of 90/60 mmHg and a pulse rateof 135 beats/min. Examination of the throatrevealed a right peritonsillar abscess, but other-wise physical examination was normal.Laboratory investigation on admissionrevealed a haemoglobin of 13.0 g/dl, whiteblood cell count of 7.6 x 109/1, and platelets14.7 x 109/1. Liver function tests, serumcreatinine and chest X-ray were normal.Incision of the abscess yielded a small amountof bloody fluid but no culture was done. Thepatient was started on intravenous cephalothin500 mg every six hours. On the fifth hospitalday he developed rapidly increasing swellinginvolving both sides of the neck and suprac-lavicular regions with crepitus. A computedtomographic (CT) scan of the chest demon-strated an abscess with gas collection in theanterior mediastinum down to the level of the

heart, bilateral pleural effusion, and pericardialeffusion (figures 1 and 2). Cephalothin wasdiscontinued and intravenous imipenem/cilastatin 500 mg every six hours was started,and surgical drainage was carried out through atranscervical incision. Culture of the pus grewStreptococcus viridans. Two days later chestX-ray showed further widening of the medias-tinum, a large left pleural effusion, and anechocardiogram showed a large pericardialeffusion. Mediastinal drainage was done againthrough a subxiphoid incision and pericardialand left pleural tubes were inserted yieldingpurulent fluids. The patient's condition thenimproved gradually and the mediastinal drain,pericardial, and left pleural tubes wereremoved on the 20th hospital day. Imipenem/cilastatin was continued for total of six weeks;the patient was then discharged home in goodhealth.

Figure 1 CT scan at the level of larynx showingextensive gas-forming infection involving both sides ofthe neck

Figure 2 CT scan at the level of the heart showingextension of the infection to the anterior mediastinumand pericardium

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Descending necrotising mediastinitis 99

Case 2A 47-year-old man with insulin-dependentdiabetes mellitus was admitted with a 24-hhistory of throat pain and trismus. Physicalexamination revealed a temperature of 37.9°C,pulse rate of 104 beats/min and blood pressure210/120 mmHg. Throat examination revealeda right peritonsillar abscess. Laboratory inves-tigation on admission revealed: a haemoglobin12.3 g/dl, white blood cell count 16.4 x 109/1,platelet 30.4 x 109/1, random blood sugar14.6 mmol, serum creatinine 220 ttmol/l, andnormal chest X-ray film. He was started onintravenous cephalothin 1.5 g every six hourswith slight improvement. On the sixth hospitalday incision of the abscess was carried out butonly a small amount of blood was obtained.Intravenous clindamycin (600 mg every sixhours) was added. On the 1 1th hospital day hedeveloped swelling in the anterior aspect of theneck and both supraclavicular regions, more inthe right side, with no crepitus. A CT scan ofneck and chest demonstrated a right peritonsil-lar abscess 3 cm in diameter and an abscessextending from the left oropharynx down to themediastinum anterior to the trachea and behindthe arch ofthe aorta with air bubbles (figures 3,4). Transcervical draining of the mediastinumwas done, but culture of the pus failed to growany organism. After that the patient continuedto improve gradually. Imipenem/cilastatin wascontinued for a total of 30 days, then he wasdischarged home in good health.

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Figure 3 Post-contrast CT scan of the neck showingan abscess in the left para-pharyngeal space with ringenhancement

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Figure 4 Post-contrast CT scan at the level of thethyroid gland, showing extension ofthe infection down-wards with the gas formation

Discussion

Acute mediastinitis is an uncommon condition;it is mostly seen as a complication ofoesophageal perforation or following cardiacsurgery. Acute mediastinitis unrelated to sur-gical procedures was considered a rare infec-tion even in the pre-antibiotic era.' Today,liberal and early antibiotic utilisation has madethis condition even more rare, but it is still seenas a complication of infection in theoropharynx, or second and third mandibularmolar with dissection downward along theanatomic fascial planes to the mediastinum.Such a variety is called descending necrotisingmediastinitis. Pearse2 in 1938 reported one ofthe first series of patients with mediastinitisfollowing orodental infections. He described100 patients, 64 of whom were the result ofoesophageal perforation while only 21 were theresult of oropharyngeal infection and in thisgroup he reported a mortality of more than50%. Over 50 further cases of descendingnecrotising mediastinitis have now beenreported.''8 We adopted the criteria proposedby Estrera et al3 for the diagnosis of descendingnecrotising mediastinitis (see box).The group consisted of 36 males, 10 females

and five patients for whom sex was notspecified. Ages ranged from one month to 64years with an average of 33.5 years. The mostcommon cause was odontogenic infectionusually arising from second and third man-dibular molars (table). Patients with acutemediastinitis are often severely ill (see boxoverleaf). Most recent studies have emphasizedthe polymicrobial nature of these infections.2"3The organisms involved in descending nec-rotising mediastinitis are usually mixed aerobesand anaerobes, accounting for 47% of cases,aerobes only (usually B-haemolytic streptococ-cus) account for 23% and anaerobes only 30%of cases.3 These usually reflect the organismspresent in the mouth. The synergistic action of

Criteria for diagnosis of descen-ding necrotising mediastinitis

* clinical manifestation of severe infection* characteristic X-ray features of mediastinitis* necrotising mediastinal infection at operation

or post-mortem* relationship to oropharyngeal infection, with

the development of the necrotising process

Table Conditions causing descendingnecrotising mediastinitis

Cause No of patients

Odontogenic infection 31Retropharyngeal abscess 6Peritonsillar abscess 3Cervical lymphadenitis 2Trauma 3Endotracheal intubation 5Unknown 1Total 51

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100 Alsoub, Chacko

Descending necrotisingmediastinitis

Clinical features* severely ill* fever, tachycardia* oedema ofneck or chest wall with crepitus* purulent pleural and/or pericardial effusion

aerobic and anaerobic organisms may explainthe virulence of these infections.

In the evaluation of cases of descendingnecrotising mediastinitis the use of X-rayexamination of the neck and chest is not veryhelpful. It may show widening of the medias-tinum with gas bubbles, however, these find-ings are usually late in the course of the disease.CT scan has proved to be a very useful aid inthe diagnosis of descending necrotisingmediastinitis and its management. It allowsearly diagnosis of the disease with greataccuracy and confidence; it aids in the choice ofthe surgical approach to drain the mediastinumand in the follow-up of patients after drainage.The management of patients with descen-

ding necrotising mediastinitis consist of anadequate surgical drainage combined withproper antibiotic choice. Because these infec-tions are usually poly-microbial with bothaerobic and anaerobic organisms, the initialantibiotic choice should cover these organismsand antibiotic combinations are often required.Later on when the culture results are availableantibiotics can be changed accordingly. Toawait the results of the culture and sensitivitystudies prior to initiation of antimicrobialtherapy, a common practice for other infec-tions, is dangerous and ill-advised.A thorough knowledge of the inter-

relationships between the fascial spaces of theneck and mediastinum is crucial to the propersurgical management of these infections.Several authors have written detailed descrip-tions of the anatomy of this region and thereader is referred to one of them.2'36 A few keypoints will be made. There are three primaryroutes of spread of infection from the neck tothe mediastinum. The pretracheal space liesanterior to the trachea and posterior to the strapmuscles and pretracheal fascia; its superiorlimit is the thyroid cartilage and it descendsinto the anterior mediastinum. At the level ofthe carina the pretracheal fascia fuses with thepericardium and parietal pleura, explaining thefrequent association of empyema and pericar-dial effusion with anterior mediastinal abscess;spread of infection along this route is notcommon, accounting for only 7% of cases ofdescending necrotising mediastinitis. Theperivascular space includes the carotid sheathand its neural and vascular structures. Involve-ment of this space may result in major vesselrupture and cranial nerve deficits. Spread ofinfection along this space accounts for about20% of cases. The most frequent route ofspread of descending infections into themediastinum is through the retrovisceral space,accounting for about 710% of cases.'3 This space

extends from the skull base inferiorly into theposterior mediastinum to the diaphragm.Infections of the second and third mandibularmolars may result in submandibular triangleabscess. By extension of the abscess beyond theposterior limit of the mylohyoid shelf, involve-ment of the retrovisceral space can occur withsubsequent involvement of the mediastinum.Spread of infection from the oropharynx to themediastinum is enhanced by gravity and thenegative intrathoracic pressure.The standard and most commonly used

approach to drain the mediastinum is thetrans-cervical approach. However, manyauthorities in this field believe that this ap-proach may be inadequate and even may delaydefinitive operation to drain the medias-tinum.34 They recommend an approach whichdepends on the CT scan finding at the time ofdiagnosis. If the superior mediastinum only isinvolved and the infection is contained abovethe level of the fourth thoracic vertebraposteriorly or tracheal bifurcation anteriorly,mediastinal drainage may be accomplished bythe trans-cervical approach. However, inpatients with infection below this level,mediastinal drainage is best accomplished bysubxiphoid or trans-thoracic drainage, in addi-tion to drainage of their cervical infections.Drainage ofthe pericardial and pleural spaces isalso necessary if they are involved. The resultsof the treatment ofour patients further supportthese recommendations. Our first patient hadextensive disease with extension below thefourth thoracic vertebra with pleural andpericardial effusion. In this patient trans-cervical drainage was not adequate and heneeded subxiphoid drainage, while the secondpatient had limited disease and in this patienttrans-cervical drainage was adequate. Animportant point in the management of thesepatients is the use oftracheostomy, which couldbe an integral part of their treatment. The useof an endotracheal tube is discouraged becauseof the risks of reintubation.'9 Several complica-tions have been reported in patients withdescending necrotising mediastinitis which in-clude compromise of pulmonary function byfluid accumulating in the pleural and extra-pleural spaces, exsanguination from vesselerosion, cranial nerve palsies (IX, X, XII), andepidural abscess.'3-32The mortality rate from descending nec-

rotising mediastinitis remains high, the reasonsfor this are: firstly, these infections tend to berapidly spreading and accompanied by a ful-minant sepsis. Secondly, there is oftensignificant delay before the diagnosis is made.Pearsel has reported a mortality of more than50% among 21 patients with mediastinitissecondary to oropharyngeal infections. Estreraet all in 1983 reported a mortality of 42%,however, since his report, another 20 patientswith descending necrotising mediastinitis havebeen reported,'5;5 "''3~5 including our twopatients, with 25% mortality. Although thismortality is still high, however, it represents a17%~drop from that reported by Estrera et al.The reasons for this drop are multifactorial, animportant one being the use of CT scanning

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Descending necrotising mediastinitis 101

which allows early diagnosis of descendingnecrotising mediastinitis and initiation oftreat-ment. The usefulness ofCT scanning was firstnoticed by Estrera et al who attributed thesurvival ofthree ofhis last four patients to earlydiagnosis using CT. Other reasons that couldhave contributed to this drop in mortalityinclude a surgical approach that more oftenuses the subxiphoid incision or thoracotomyand not only the transcervical incision to drainthe mediastinum, the use of modernantibiotics, and intensive care management.

Conclusion

Descending nectrotising mediastinitis secon-dary to oropharyngeal infection is rare. Themortality is 25% for cases reported in the last10 years. The treatment depends on accurateand prompt diagnosis. CT scanning is thesingle most important tool for the early diag-nosis of descending necrotising mediastinitis.Early and complete mediastinal drainage via

Descending necrotisingmediastinitis

* rare* oedema ofneck and chest wall, with crepitus,

are the classical signs* CT scanning is useful in early diagnosis* mediastinal drainage and antibiotic therapy

are the treatment of choice* mortality 250%

trans-cervical incision or using a thoracotomyor subxiphoid incision, along with antibiotictherapy, provide the basis for treatment inthese patients.

The authors are indebted to Mr Kochuplavilayil DanielJohn for his secretarial help in the preparation of themanuscript.

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