Detection of soft tissue emphysema in emergency head and neck imaging

INTRODUCTION

It is uncommon to find soft tissue gas in routine clinical practice in head and neck radiology. In emergency imaging, the presence of soft tissue emphysema often points to certain urgencies, particularly in infective and posttraumatic settings. In this report, we highlight the various conditions with soft tissue emphysema detected in the emergency head and neck imaging, and these can be categorised into infective, traumatic, iatrogenic and various other causes.

INFECTION

Neck abscess [Figure 1]

Figure 1.

A 63-year-old woman presents to the emergency department with sore throat and dyspnoea. (a) Lateral radiograph of the neck shows swelling of the epiglottis (long arrow) and marked swelling/oedema of the submandibular (short arrow) and prevertebral (arrowhead) soft tissues. These resulted in significant narrowing of the laryngeal airway. (b) Axial and (c) coronal contrast-enhanced CT images show gas loculi (arrows) within the rim-enhancing fluid collections, which extend from bilateral submandibular spaces to the anterior cervical space, limited laterally by the sternocleidomastoid muscles. Abscesses in the prevertebral (arrowhead, b) and anterior cervical spaces extend inferiorly into the superior mediastinum (arrowhead, c). These extensive neck abscesses were surgically evacuated and the patient was treated with broad-spectrum antibiotics. (d) Axial contrast-enhanced CT image after adequate treatment shows a significant reduction of the neck abscess.

Abscesses can be located in either superficial or deep layers of the neck. Superficial neck abscesses usually result from an infection in the lymph node or lymphadenitis.[1] Deep neck abscess is defined as a collection of pus in the fascial planes and spaces of the head and neck. The incidence of deep neck abscess was reported to be 2.64 per 100,000 according to the National Health Insurance System of Taiwan.[1] The widespread availability of antibiotics has drastically reduced the incidence of neck abscesses. However, these are challenging cases with potentially life-threatening complications. The diagnosis is often delayed due to the insidious presentation of the patient’s symptoms. The common microorganisms isolated in deep neck infections include both aerobes and anaerobes with a predominance of oral flora; these include Streptococcus, Staphylococcus, Escherichia coli, Bacteroides, Pseudomonas and Haemophilus influenzae.[1] Occasionally, Mycobacterium tuberculosis is isolated from cervical lymphadenitis and abscesses, particularly in immunocompromised and elderly individuals.[1]

Conventional radiographs often demonstrate widening of the prevertebral soft tissue with gas lucencies. Multidetector computed tomography (MDCT) typically demonstrates a central hypodense collection with peripheral rim enhancement, which occasionally contains gas loculi.[2] It is a useful modality to delineate the extent and location of the abscess collection in the neck spaces.

The possible complications of deep neck infections are: (a) airway obstruction from tracheal compression, (b) spondylodiscitis or osteomyelitis due to posterior extension of infection into the prevertebral space, (c) mediastinitis from the inferior extension of infection, and (d) vascular complications such as mycotic pseudoaneurysm of the cervical carotid artery and thrombosis of the internal jugular vein (IJV), including thrombophlebitis with distant spread of oropharyngeal infection, also known as Lemierre syndrome.[2]

Adequate antimicrobial coverage, surgical drainage and appropriate management of complications remain the cornerstone of treatment for deep neck abscesses. Ultrasound-guided needle aspiration is an effective alternative for small abscess collections without airway compromise.[3]

Necrotising epiglottitis [Figure 2]

Figure 2.

A 57-year-old man presented to the emergency department with persistent fever and odynophagia, not improving with antibiotics. (a) Axial and (b) coronal contrast-enhanced CT images show an oedematous epiglottis (arrows) containing gas loculi with inflammatory changes in the surrounding soft tissue. (c) Laryngoscopic image shows an oedematous epiglottis containing pus (arrowheads). This is consistent with acute necrotising epiglottitis. The patient underwent an endoscopic incision and drainage of the abscess. Streptococcus species were isolated. The patient’s condition improved following treatment with intravenous and oral antibiotics.

Epiglottitis is characterised by severe inflammation of the supraglottic region involving the epiglottis and aryepiglottic folds, leading to acute airway obstruction.[4] It used to be a life-threatening condition over an 8-year period from 1992 to 1999 when H. influenzae Type B (Hib) immunisation was not routinely administered.[4] The incidence of this condition has dropped significantly since the introduction of Hib vaccination.[4] Necrotising epiglottitis is an extremely rare form of epiglottitis with only a few cases reported in the literature, particularly involving the immunocompromised.[5] Computed tomography (CT) typically shows an oedematous epiglottis containing air loculi. Prompt recognition of this rare entity is essential because delayed treatment can lead to airway compromise and locoregional spread, and dissemination of infection.[4] Surgical debridement and abscess drainage along with broad-spectrum antibiotic therapy are the mainstay treatments. Occasionally, surgical flaps and reconstruction may be required, but the recovery period can be prolonged.[4]

Necrotising fasciitis [Figure 3]

Figure 3.

A 46-year-old man presented to the emergency department after he was found unresponsive. He had a history of recent dental extraction complicated by a submandibular abscess. (a) Lateral radiograph of the neck shows a severe widening of the prevertebral space (arrowhead) with diffuse soft tissue swelling and emphysema (arrow). (b) Axial and (c) coronal CECT images show diffuse soft tissue swelling in the neck with extensive gas loculi within low-density fluid collections (arrows). (d) Axial CECT image of the chest shows the spread of infection into the mediastinum with extensive pneumomediastinum (arrow). The overall findings are compatible with necrotising fasciitis. Postsurgical debridement (e) coronal CECT image shows a significant reduction of the soft tissue emphysema in the neck. CECT: contrast-enhanced computed tomography

Also known as the ‘flesh-eating disease’, necrotising fasciitis (NF) is a serious and potentially life-threatening inflammatory condition of the neck, with abscess formation within the deep cervical fascia.[5] The incidence of NF in the UK was 21 per million population in 2017.[6] Head and neck involvement of NF is uncommon, having an insidious onset with regional neck swelling, erythema and fever.[5] If untreated, this condition inevitably leads to descending necrotising mediastinitis with a mortality rate of between 25% and 40%.[5] The most specific finding on imaging is detection of gas within fluid collections that tracks along the fascial planes.[5] Secondary signs of inflammation include fat stranding, oedema and thickening of the cervical fascias. The most common microorganisms isolated are Streptococcus pyogenes and group A Streptococcus bacteria.[5] Treatment consists of early and aggressive surgical debridement of necrotic tissues along with broad-spectrum antibiotic therapy. Without surgical debridement, the mortality rate is almost 100%.[5]

COVID-19 pneumonia-related pneumomediastinum [Figure 4]

Figure 4.

A 60-year-old man presents to the emergency department with fever, cough and shortness of breath. He has a positive PCR test for SARS-CoV-2. (a) Chest radiograph (supine view) shows patchy consolidation in both lungs and pneumomediastinum (arrowhead), with extensive subcutaneous emphysema extending to the lower neck and supraclavicular region (arrows). (b) Coronal CT neck (lung window) image shows the extent of the pneumomediastinum and soft tissue gas within the neck spaces, which extends superiorly to the parapharyngeal spaces and skull base (arrows). (c) Post-intubation coronal CT chest (lung window) image shows progression of the COVID-19 pneumonia with a crazy-paving pattern (arrowhead), which is one of the typical radiological findings for novel viral pneumonia. Besides pneumomediastinum, there is extensive subcutaneous emphysema in the right chest wall and axilla, as well as the supraclavicular regions and both sides of the image lower neck (arrows). PCR: polymerase chain reaction, SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.

Pneumomediastinum is defined as the presence of extraluminal gas within the mediastinum. It is a relatively rare condition, with a reported incidence of approximately 1/44,500 emergency department (ED) admissions in a hospital in Spain over 26 years.[7] Pneumomediastinum is a rare complication of coronavirus disease 2019 (COVID-19) pneumonia. It could result directly from the pathogenesis of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) rupture of pulmonary bullae or secondary to intensive care management due to airway trauma during tracheal intubation, barotraumas or repositioning manoeuvres.[8] Besides, it can be associated with subcutaneous emphysema of the chest with superior extension to the neck [Figure 4]. Treatment is supportive and conservative in most cases.[8]

Emphysematous osteomyelitis with paravertebral gas [Figure 5]

Figure 5.

A 64-year-old man presented to the emergency department with fever and neck pain for 1 week. His blood culture grew Streptococcus constellatus. (a) Coronal and (b) axial CT cervical spine (bone window) images show osteomyelitic lesions involving the C7 and T1 vertebral bodies (arrowheads), with multiple gas loculi distributed in the C7–T1 disc space, heads of bilateral first ribs and paravertebral regions (arrows). (c) Axial CT (bone window) and (d) axial T1-W postcontrast MR images of the cervical spine show multiple intraosseous gas loculi (arrowheads) and rim-enhancing abscess collection (connector arrow, d) within the T1 vertebral body. There is extension of infection to the surrounding paravertebral soft tissue with abnormal enhancement and gas loculi (arrow). The presence of multiple intraosseous gas loculi and abscess, as seen in this case, is referred to as the ‘pumice stone sign’. These imaging features are consistent with emphysematous osteomyelitis. The patient was treated immediately with broad-spectrum intravenous antibiotics (tazocin, meropenem and ceftriaxone) for 8 weeks before being switched to oral amoxicillin. The patient has a good outcome with complete recovery.

Emphysematous osteomyelitis is a rare and fatal disease. It is characterised by extensive intravertebral gas, bone oedema and/or associated paravertebral collections. The most common isolated causative organisms include an anaerobe or members of the Enterobacteriaceae family, including E. coli, Klebsiella pneumoniae, Bacteroides species and Fusobacterium; these are all gas-forming bacteria. Occasionally, Streptococcus constellatus, a normal oral flora, can also cause purulent infections [Figure 5]. The most common associated comorbidity is diabetes mellitus.[9] Haematogenous spread is the most common mode of dissemination of infection.[9] Imaging with MDCT or magnetic resonance imaging (MRI) is characterised by the presence of intraosseous gas accompanied by bone and soft tissue infection. The typical imaging features are clusters of intramedullary and paravertebral gas loculi ranging between 2 mm and 5 mm in size, resembling the surface of a pumice stone.[9] It is referred to as the ‘pumice stone sign’. Empirical antibiotic therapy directed against the Enterobacteriaceae family and anaerobes should be administered immediately after diagnosis.[9]

TRAUMA

Laryngeal injury with cricoid fracture [Figure 6]

Figure 6.

A 35-year-old male food delivery driver presented to the emergency department after he collided with a barricade in a road traffic accident. He sustained a soft tissue injury with a skin laceration on his neck after hitting a metal chain from the barricade. (a) Axial contrast-enhanced, (b) axial bone window and (c) sagittal CT neck images show significant soft tissue emphysema (arrow, a) surrounding the cricoid and thyroid cartilages, and a fracture of the right side of the cricoid cartilage (arrow, b) as well as a laryngeal mucosal tear (arrowhead, b and arrow, c). The patient’s condition improved subsequently following wound washout, tracheostomy and endolaryngeal microsurgery.

Cricoid fracture is a rare condition. Its incidence has been reported to be approximately 1 in every 30,000 adult emergency visits in the USA.[10] About 97% of laryngeal trauma is due to blunt trauma, with 39% caused by a sports injury and 33% by physical trauma.[10] The main imaging modality to detect abnormalities of the laryngeal skeleton, airway and soft tissues is MDCT. The most concerning complication in the acute setting is subglottic stenosis due to mucosal oedema. Other complications such as tracheo-oesophageal fistula can occur many years after the initial laryngeal injury.[10] Treatment options are divided into medical and surgical management. Medical management includes voice rest with humidified air for minor injuries or mucosal tears <2 cm. Surgery is indicated for unstable airway, large mucosal laceration or markedly displaced fracture of the laryngeal skeleton.[10]

Facial bone fracture [Figure 7]

Figure 7.

A 44-year-old man presented to the emergency department following an assault with injury to his face. (a) Axial CT facial bone image shows a displaced fracture of the left maxillary sinus anterior wall (arrow) with subcutaneous emphysema. (b) Coronal CT facial bone image shows a displaced fracture of the left orbital floor with involvement of the infraorbital canal (arrow). This resulted in extensive subcutaneous emphysema in the left periorbital and left hemifacial regions. (c) Sagittal CT facial bone image shows a displaced fracture of the anterior wall of the left maxillary sinus, left inferior orbital rim and floor of the left orbit (connector arrow) with surrounding soft tissue emphysema.

Traumatic fractures of the orbito-zygomaticomaxillary complexes can be associated with subcutaneous emphysema due to a breach of the paranasal sinuses. Complications related to facial bone fractures, such as impingement of the temporalis tendon, can cause trismus; other complications include impingement of the infraorbital nerve and extraocular muscle, and/or infraorbital nerve entrapment leading to diplopia or enophthalmos.[11] The preferred imaging for diagnosis and delineation of the types of fractures and associated complications is MDCT of the face.[12] Nondisplaced fractures are usually treated conservatively.[12] Surgical repair is often required for displaced fractures with extraocular muscles or neurovascular compromise.[12] Likewise, surgery is performed for cosmetic purposes.[12]

Ingestion of foreign body with perforation of the posterior pharyngeal wall [Figure 8]

Figure 8.

A 43-year-old man presented to the emergency department with persistent throat pain after swallowing a chicken bone. (a) Lateral radiograph shows a small rectangular-shaped bone (arrow) with gas loculi in the thickened prevertebral soft tissue (double-headed arrow). (b) Axial CT image shows a radiopaque chicken bone fragment (arrow) in the pharyngo-oesophageal junction with adjacent gas loculi (arrowhead). During surgery, the small piece of chicken bone was removed from the perforated posterior pharyngeal wall, along with the evacuation of a small abscess collection.

Foreign body (FB) ingestion commonly occurs in children between the ages of 6 months and 3 years.[1] In adults, FB can be ingested accidentally with food, especially in edentulous elderly patients. The initial examination with lateral neck radiographs can be limited due to the presence of nonradiopaque FB and obscuration of the cervicothoracic junction by the shoulder. Regardless of these limitations, it is imperative to recognise secondary radiographic signs of complications following FB ingestion, such as the presence of gas in the retropharyngeal soft tissue and prevertebral air–fluid level, indicating perforation and abscess, respectively.[13] Nonenhanced CT should be considered in the event of a nondiagnostic lateral neck radiograph or doubtful calcification of the laryngeal or thyroid cartilages.

IATROGENIC CAUSES

Post-tracheostomy and central venous line placement [Figure 9]

Figure 9.

An 82-year-old man with a known supraglottic carcinoma had a tracheostomy tube inserted about 1 week ago. (a) Chest radiograph shows the presence of a tracheotomy tube (arrowhead) and significant subcutaneous emphysema in the supraclavicular fossa (white arrow) and base of the neck (black arrow). (b) Axial CT neck (lung window) image shows the presence of a tracheostomy tube (arrowhead) and extensive soft tissue gas scattered in the supraclavicular and base of the neck (black arrows). (c) Axial CT neck image shows effacement of the laryngeal airway (white arrow) caused by a supraglottic mass (black connector arrow). Note the diffuse gas loculi (straight black arrows) scattered in the surrounding soft tissue. Besides, there is an enlarged right level II/III cervical node with necrosis (star) along with adjacent gas loculi.

Pneumomediastinum can also occur due to iatrogenic causes such as endoscopic procedure with injury to any air-filled structures in the chest, such as the lungs, trachea, central bronchi and oesophagus. Tracheostomy and central line insertions are common procedures performed in the intensive care units. Injury to the parietal pleura during central line placement can result in pneumomediastinum and pneumothorax with subcutaneous emphysema extending to the neck. As with all airway access procedures, tracheostomy with prolonged tracheal tube placement has been associated with possible risks such as pneumothorax, pneumomediastinum, tracheal rupture, scarring and tracheo-oesophageal fistula.[14] Occasionally, free gas can escape into the surrounding soft tissue from tracheostomy, resulting in subcutaneous emphysema.[7] Likewise, penetrating trauma of the neck and chest can result in extensive subcutaneous emphysema and pneumothorax, respectively.[14]

Post-dental procedure [Figure 10]

Figure 10.

A 29-year-old man presented with throat pain after undergoing a dental procedure. (a) Lateral radiograph of the neck shows the presence of gas loculi in the prevertebral space (arrow) and subcutaneous layer of the neck (arrowhead). (b) Coronal CECT neck image shows extensive soft tissue emphysema centred at the left angle of the mandible, with extension of gas into the left parapharyngeal (arrow), submandibular (star), masticator (arrowhead) and visceral spaces around the left thyroid gland (black arrow) as well as the left supraclavicular fossa (curved arrow). CECT: contrast-enhanced computed tomography

Subcutaneous emphysema related to dental procedures is a rare complication that can be divided into iatrogenic and infectious aetiologies. The most common cause is iatrogenic, with inadvertent injury to the pulps or gum tissues. Infections can occur subsequently with abscess formation.[15] Post-dental procedure emphysema has been described following root canal treatment and dental extraction.[15] It can be associated with the use of high-speed dental drills as well as air and water dental syringes.[15] It has been postulated that air is inadvertently driven into the subcutaneous tissue through tiny gaps between the teeth and the gums, spreading along the cervical fascial planes. There could be an inferior extension of air causing pneumomediastinum as more air is being introduced.[15] Typically, CT images show air tracking down the involved side of the neck and mediastinum, outlining the structures without any extension into the muscles and organs. There is a risk of migration of microorganisms from the oral flora into the mediastinum, causing infective mediastinitis with significant mortality.[15] Treatment is usually conservative with the administration of empirical broad-spectrum antibiotics.[15]

Pneumoparotid [Figure 11]

Figure 11.

A 45-year-old man presented to the otorhinolaryngology clinic with left parotid swelling after having had a dental filling procedure on his left upper molar tooth (2 days before). (a) Axial and (b) coronal CT images show a mildly swollen left parotid gland with an unusual tract of gas along the course of the left parotid duct (arrows).

A rare condition, pneumoparotid refers to the presence of air within the parotid gland, resulting in unilateral or bilateral parotid swelling. Patients are usually well with painless mild swelling of the parotid gland. Occasionally, gas loculi are introduced into the parotid gland iatrogenically during dental procedures using air-powered dental drills.[16] Likewise, players of wind instruments (e.g. windpipes and flutes) and glass-blowers are at risk of getting occupational-related subcutaneous emphysema.[16] The most sensitive imaging modality to detect gas loculi within the soft tissues is CT.[16] Treatment is targeted towards minimising the risks of pneumoparotid and subcutaneous emphysema, for example, by technique modification of wind instrument players. Recognition of this benign condition is essential to avoid unnecessary surgical intervention. Surgery is only reserved for chronic or recurrent pneumoparotid.[16]

OTHER CAUSES

Spontaneous pneumomediastinum [Figure 12]

Figure 12.

A 25-year-old man presented to the emergency department with ‘subcutaneous crepitus’ over bilateral supraclavicular regions after weightlifting in the gym. (a) Lateral neck radiograph shows extensive soft tissue emphysema in the neck, particularly in the prevertebral region (arrow), which extends superiorly as far as the craniovertebral junction (arrowhead). (b) Coronal noncontrast CT chest and (c) neck images (lung window) show pneumomediastinum (white arrows) with subcutaneous emphysema at the base of the neck and the supraclavicular region (black arrows). The patient was monitored for 24 h. He showed subsequent reduction of pneumomediastinum and soft tissue emphysema and was discharged with symptomatic treatment.

Pneumomediastinum or pneumothorax can occur spontaneously with injury to any air-filled structures in the chest, such as the lungs, trachea, central bronchi and oesophagus. Individuals with underlying respiratory disease are more susceptible to these conditions, particularly after strenuous physical exercise or forceful exertion. Besides symptomatic treatment with analgesics and antitussive medications, oxygen administration via nasal cannula can help to improve gas reabsorption in the chest.[7]

Subcutaneous emphysema related to Boerhaave syndrome [Figure 13]

Figure 13.

A 73-year-old man presented to the emergency department with forceful vomiting, chest pain and subcutaneous emphysema. (a) Coronal CECT chest (posterior) image shows rupture and leakage of contrast and gas loculi from the distal oesophagus into the left hemithorax (arrows) resulting in large left hydropneumothorax (arrowheads). (b) Coronal CECT chest image and (c) CECT chest (lung window) image show subcutaneous emphysema extending up to the base of the neck and the supraclavicular region (arrows), along with left pleural effusion (white arrowheads) and pneumothorax (black arrowheads). He underwent surgical repair of the oesophageal perforation. Postoperatively, it was complicated by recurrent pneumonia and subpleural abscess, which required drainage. CECT: contrast-enhanced computed tomography

Boerhaave syndrome was named after Herman Boerhaave, a Dutch professor who first reported an oesophageal rupture secondary to forceful vomiting in 1724.[17] This uncommon entity can be induced by abrupt increased intraoesophageal pressure caused by other straining activities, including retching, weightlifting, childbirth and even defaecation.[17] Patients may present with severe vomiting, sudden chest pain and subcutaneous emphysema.[17] Radiological findings include hydropneumothorax, pneumomediastinum and subdiaphragmatic gas. It can be a rare cause of subcutaneous emphysema in the neck when gas extends superiorly from the chest. Prompt recognition of this condition is vital, as it is a potentially life-threatening condition. Complications include mediastinitis and sepsis, with a mortality rate as high as 35%.[17] Traditional treatment consisted of operative repair of oesophageal perforation.[17] Endoscopic management with stent placement has changed the management of oesophageal perforation.[17]

CONCLUSION

Diagnostic imaging is of paramount importance for prompt diagnosis of soft tissue emphysema and to guide patient management. Multidetector computed tomography is essential in identifying the aetiology, source and location of soft tissue emphysema. In traumatic settings, soft tissue emphysema can be due to fractures of the facial bones or laryngeal injury. In nontraumatic settings, the identification of soft tissue emphysema can be associated with either infective iatrogenic or other causes.

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Conflicts of interest

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SMC CATEGORY 3B CME PROGRAMME

Online Quiz: https://www.sma.org.sg/cme-programme

Deadline for submission: 6 pm, 08 November 2024

Question: Answer True or False
1. Regarding neck abscess:
(a) Airway compression is a possible complication.
(b) Posterior extension may cause osteomyelitis.
(c) Thrombosis of the internal jugular vein is a possible complication.
(d) Ultrasound-guided needle aspiration is an effective alternative for small neck abscess collections without airway compromise.
2. Regarding pneumomediastinum:
(a) Pneumomediastinum is relatively common and should be considered in an acute setting.
(b) COVID-19 pneumonia-related pneumomediastinum is relatively common and should be considered.
(c) COVID-19 pneumonia-related pneumomediastinum is managed by supportive treatment.
(d) COVID-19 pneumonia-related pneumomediastinum can also be secondary to intensive care unit management.
3. Regarding emphysematous osteomyelitis:
(a) One of the most important signs to recognise in emphysematous osteomyelitis is the ‘pumice stone’ sign.
(b) Another important sign to recognise in emphysematous osteomyelitis is the ‘cobblestone street’ sign.
(c) The most common associated comorbidity in emphysematous osteomyelitis is chronic renal failure.
(d) Haematogenous spread is the most common dissemination of infection in emphysematous osteomyelitis.
4. Regarding subcutaneous emphysema and pneumoparotid:
(a) Subcutaneous emphysema can be caused by post-dental procedure.
(b) Subcutaneous emphysema caused by post-dental procedure also carries the risk of infective mediastinitis.
(c) Pneumoparotid is an urgent condition and requires immediate surgical intervention.
(d) Pneumoparotid, if left untreated, may cause chronic atrophy of the parotid gland.
5. Regarding trauma:
(a) Cricoid fracture will always require surgical intervention.
(b) Facial bone fracture can cause impingement of the temporalis tendon and trismus.
(c) Facial bone fracture can cause infraorbital nerve entrapment, resulting in diplopia or enophthalmos.
(d) Facial bone fractures that are nondisplaced can be treated conservatively.