Unusual cause of airway obstruction: subglottic oncocytic cyst

Abstract

Oncocytic cysts are rare benign cystic lesions, which are usually seen in the supraglottic region. They usually present with symptoms of hoarse voice or the sensation of a lump in the throat. Management is with complete excision and follow-up to monitor for recurrence. In this unusual case, an elderly woman presenting with shortness of breath following recent treatment for pneumonia developed rapidly worsening stridor during admission. Flexible nasal endoscopy revealed a large pedunculated cystic lesion arising from the subglottic laryngeal mucosa. A tracheostomy was performed as an emergency and the lesion was then excised. Histology confirmed the diagnosis of a benign oncocytic cyst. Although oncocytic cysts are a recognised benign pathology of the supraglottic larynx, they should remain in the differential diagnosis for the subglottic larynx. Management is based on cases of supraglottic pathology, and we advise careful monitoring for this previously unreported pathology.

Background

Oncocytic cysts or onocytomas are rare neoplastic lesions which are characterised histologically by having a cyst lining predominantly featuring oncocytes. The term oncocyte, describes large cells with an eosinohpillic granular cytoplasm and an abundance of mitochondria due to mitochondrial DNA changes, usually deletions.¹ Oncocytic tumours can be found in the thyroid, parathyroid, pituitary, adrenal, kidney, salivary glands and soft tissues, although there are phenotypical differences between those found in the salivary tissues and other organs. The reason for oncocytic neoplasm formation at these sites is thought to be due to the low proliferative rate of these cells.

Oncocytic cysts in the head and neck are very rare, accounting for only 1% of neoplasms in the major salivary glands. Although oncocytic lesions are more commonly in the major salivary glands, they have been identified in the sinonasal tissues, bronchus, nasopharynx and larynx, associated with minor salivary gland tissue. Oncocytic lesions of the minor salivary glands are even less common, however, oncocytic cells have been reported in up to 11% of cystic laryngeal lesions.² Laryngeal lesions arise most commonly from the supraglottic larynx, laryngeal ventricles, ventricular folds or aryepiglottic folds, and rarely from the vocal cords themselves (glottis). They are most commonly identified between 70 and 90 years of age and are more common in women. There is usually a positive smoking history.³While most reported cases describe a single lesion there are examples of bilateral or multiple oncocytic cysts. Our case is the first reported oncocytic cyst found to arise from the subglottic larynx.

Oncocytic lesions are usually benign, however, malignant transformation to an oncocytic carcinoma is possible. Malignant potential is low due to the low proliferative rate of these cells, however, the risk is higher in those arising from minor salivary glands, compared with major salivary glands. Given the very low case numbers, exact rate of transformation is unclear.⁴

The presentation of patients with laryngeal cysts is usually with sensation of a foreign body in the throat or hoarseness of voice, although throat pain may also be a symptom.^{3 5}

Acute stridor is a rare but recognised presentation.⁶ Management of these lesions is twofold, first airway control, and second diagnostic excision. Recurrence rates are very low and where all tissue is excised there is no role for adjuvant therapy.³ In the event that airway control cannot be obtained by traditional intubation techniques, an awake fibre-optic intubation or a tracheostomy should be considered to secure the airway. The presence of a subglottic lesion could complicate a tracheostomy procedure, therefore care should be taken when the full extent of the lesion is unknown.

Case presentation

In this unusual case a 78-year-old ex-smoker presented with shortness of breath following recent treatment for pneumonia. She was treated for recurrent chest infections for the last 3 months, but apart from that she had no significant medical history, no allergies and was not taking any regular medications. However overall, she was in a frail state from recurrent episodes of pneumonia.

At initial presentation she was noted to have an audible wheeze and some hoarseness of voice. Auscultation of the chest found a bilateral wheeze with crackles at the right base with air entry throughout. A plain film chest X-ray showed ongoing radiological signs of a previous community acquired pneumonia, haziness and loss of costophrenic angle at the right base. She was therefore under the care of the medical team for a resolving lower respiratory tract infection with postinfective hyper-reactivity. She was treated supportively with oxygen therapy, continuation of the course of oral antibiotics and slow intravenous fluids.

12 hours after admission she developed rapidly worsening shortness of breath with loud biphasic stridor. Urgent referral was made to the Otolaryngology (ENT) team who performed assessment of her airway with flexible nasendoscopy. This revealed a large, smooth pedunculated lesion from the subglottic region, approximately a few centimetres in length and almost as wide as the laryngeal inlet, causing significant partial obstruction (see figure 1). With respiration, the lesion emerged between the vocal cords creating a ball-valve effect airway obstruction and stridor. When the cyst emerged through the laryngeal inlet it prevented normal adduction of the vocal cords, due to a physical obstruction, explaining her dysphonia.

Figure 1.

Larynx and cyst as seen on flexible nasal endoscopic examination.

In light of the increasing work of breathing, along with an identified airway lesion, this case was treated as an impending airway crisis. She was commenced on high-flow oxygen and transferred to the ENT unit for urgent laryngoscopy and excision of subglottic lesion, with a view to performing a tracheostomy to secure her airway. She was transferred directly to emergency theatres for anaesthetic assessment and immediate surgical intervention.

Investigations

Preoperative imaging was not obtained due to the risk of airway obstruction in this case.

Differential diagnosis

Differentials for acute stridor include infective, inflammatory and malignant pathology of the upper airway. Regardless of diagnosis, securing a safe airway is the primary aim of initial management, and histology is mandatory for confirmation of diagnosis. In cases of biphasic stridor, differential diagnoses included infective causes, such as supraglottitis, benign lesions, such as like mucous retention cysts or laryngeal polyps, as well as neoplastic causes such as laryngeal carcinoma.

Management

In the operating theatre the airway was secured with awake fibre-optic intubation. A size 5 microlaryngoscopy tube (MLT) was inserted which easily displaced the lesion. Under general anaesthetic, the ENT team performed direct laryngoscopy, where the subglottic lesion was identified, and its pedicle was seen arising from the anterior tracheal wall, just below the level of the cords. However, the due to its size, full excision was not possible with the MLT tube present. A decision was made to perform a tracheostomy below the level of the pedicle, to aid excision. Once the airway was secured with a tracheostomy, a suspension laryngoscope was inserted and positioned to gain visualisation of the laryngeal inlet and subglottic lesion. An operating microscope was also used for visualisation to allow for hands-free use of laryngeal instruments. Cold steel excision of the lesion was performed with laryngeal forceps and scissors. Unfortunately, intraoperatively the lesion ruptured revealing the lesion to be a large cyst, with thick white fluid. The cystic contents were cleared and the cyst wall and pedicle were fully excised from the anterior tracheal mucosa. There was no underlying defect of the trachea at the site of the cyst. There was minimal bleeding and haemostasis was achieved with topical application of dilute epinephrine.

Outcome and follow-up

Histological examination showed a collapsed cystic structure of the subglottic area. H&E staining demonstrated the cyst to be lined with swollen collumnar epithelial cells with an abundance of granular eosinophillic cytoplasm and round nuclei. There was no evidence of mitosis, necrosis or atypia and no suggestion of malignant invasion. There was evidence of normal tracheal stroma and mucosa as well as minor salivary glands within the adjacent tissues. Due to the friable nature of the lesion it was not possible to comment on the margins and histological completeness of the resection.

Findings were in keeping with a simple benign oncocytic cyst (see figure 2). Unfortunately, our patient had a long and complicated inpatient stay relating to her frail preoperative condition. With the tracheostomy in situ, she had significant swallowing difficulty and nasogastric feeding was initiated and managed by the nutrition team. She also had worsening of her pneumonia and a further episode of hospital-acquired pneumonia, requiring further medical input and prolonged antibiotic treatment. During this period she developed increasing oxygen requirements. A CT pulmonary angiogram was performed which also revealed bilateral pulmonary emboli (PE) on a background of mild emphysematous change, and she was started on warfarin for anticoagulation. The resolving pneumonia and bilateral PE deteriorated her respiratory function and the initial tracheostomy decannulation attempt at 1 week post-tracheostomy insertion was unsuccessful. This was delayed until her respiratory function improved as an inpatient. Her swallowing improved with time and she could safely tolerate a mashable diet and normal fluids, which was close to her preadmission diet. She was eventually decannulated 4 weeks postprocedure and discharged soon after. Flexible nasendoscopy examination prior to discharge showed that her airway had no recurrence of cyst and normal vocal cord movement.

Figure 2.

Oncocytic cyst wall resting on fibrous stroma of trachea. H&E stained ×10 magnification.

At 6 months following excision, our patient remains well and has not had further episodes of respiratory problems including pneumonia, and no hospital admissions. Repeat flexible nasendoscopy in clinic showed no recurrence of the cyst at 6 months. She will continue to be under outpatient review, at 6–12 monthly intervals.

Discussion

There are numerous cases reporting supraglottic laryngeal oncocytic cysts,2 3 5 7 however our case is the first to report one arising from the subglottic epithelium. Oncocytic cysts are generally described as solitary lesions, although there have been reported cases of presentation with multiple laryngeal oncocytic cysts.^{3 8} Presentation is usually due to alteration of voice or the persistent sensation of a foreign body in the throat, although there are reported cases of presentation with acute stridor, such as in this case. Recurrent pneumonia has not been previously associated with laryngeal oncocytic lesions.

Literature for supraglottic lesions suggests that, where the cyst has been fully excised, the risk of recurrence is low,^{3 7} however, follow-up is recommended for all laryngeal cysts as there can be a renewed risk to the airway. Supraglottic lesions are usually identified earlier due to the impact they have on voice quality, this is often absent in subglottic lesions and a small recurrence may remain asymptomatic until it reaches a critical size causing obstruction. Therefore, regular review with flexible nasendoscopy should be conducted to monitor for recurrence.

Our patient was unusual in that she did not present with symptoms until it was at a critical airway state of near-complete obstruction. This could be explained by the position of the oncocytic cyst. As it arose from the subglottic tracheal mucosa, it would not cause voice change or swallowing difficulty which vocal cord or supraglottic lesions typically present with. Therefore this lesion only presented with airway symptoms at a late stage. In retrospect, considering her history of recurrent chest infections, this may have been the only sign of her underlying pathology. The subglottic oncocytic cyst would have caused an increased work of breathing and shortness of breath due to tracheal obstruction in earlier episodes of pneumonia. As an average adult trachea has an internal diameter of around 2.5 cm and is 10 cm length, the cyst would have to reach a critical and large size before it caused symptoms of stridor and airway distress.⁹ Our patient did have a lower respiratory tract infection, which would have also caused respiratory mucosal inflammation, further aggravating the airways and mucosa.

Learning points.

• Oncocyctic cysts, although rare, can also arise in the subglottic larynx.

• Primary management of subglottic cysts causing obstruction must focus on safe control of the airway.

• Full excision of the cyst at the time of primary surgery is important to reduce the risk of recurrence.