Address for correspondence : Sang Duk Hong, MD, Department of Otorhinolaryngology-Head and Neck Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea
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Introduction

Parotid gland swellings are usually caused by viral and bacterial infections. Among the causes of non-infectious swellings, pneumoparotid is a rare condition which refers to the pathologic state of air within the parotid gland. This condition has been described in the medical literature under several names such as pneumoparotid, pneumoparotitis, pneumosialadenitis, wind parotitis, and pneumatocele glandulae parotis.¹⁾ The mechanism that causes the air reflux is an excessive increase in intraoral pressure.²⁾ Patients typically present with painless swelling in the parotid region. There is crepitus on palpation of the gland, and frothy saliva or air bubbles may be observed emanating from Stensen's duct during massage of the gland.³⁾ Here, we report an unusual case of pneumoparotid initially presented with viral parotitis in the epidemic area of mumps.

Case

A 19-year-old army soldier was initially referred to the hospital for management of rapidly increased right parotid swelling. His army group was in the epidemic area of mumps. He was hospitalized in the army hospital for the mumps. On the third hospital day, his parotid swelling rapidly increased and developed the swelling of the neck. He was then referred to our hospital. The patient never played a wind instrument, and he denied any nervous tic or habit of blowing out his cheek as well as any recent dental treatment. His army rank was private which is the lowest class in the army. He had a mild cough when he was admitted in the army hospital. However, he was worried about coughing sound that could bother his superiors at night, so he coughed with covering his mouth. His body temperature was 37.8℃ using nonsteroidal anti-inflammatory drugs.
Palpation of the gland and the neck showed tenderness and a crackling sensation. In the blood test, white blood cell count was 11100/mm³ with normal neutrophil and lymphocyte counts, and elevated serum amylase count (598 U/mL). A CT scan of the neck showed extensive air in the ductal system with extension into the soft tissue from the skull base to the lung apex (Fig. 1A and B). Chest CT scan revealed pneumomediastinum, but no evidence of fluid, abscess, or pneumothorax (Fig. 1C). We diagnosed pneumoparotid and pneumomediastinum superimposed with mumps. He was admitted into the isolated ward to seclude a patient due to presumed mumps. Mumps immunoglobulin G and M in blood were 1.98 (positive>1.2) and 0.85 (0.8Fig. 2). However, he complained of tenderness on the right parotid gland and the serum amylase were still elevated (514 U/mL). We assumed that his pneumoparotid subsided and viral parotitis was sustained. Thus, He was isolated for another 5 days without specific treatment and then discharged. He had no health consequences during nine month after discharge.

Discussion

Pneumoparotid refers to air within the parotid gland with or without inflammation. This condition may be categorized as occupational or self induced. However, regardless of the cause, it is usually caused by an increase in intraoral pressure and subsequent retrograde flow of air through Stenson's duct and into the parotid acini.⁴⁾ Most commonly, pneumoparotid is self-induced via forced retrograde pneumatic autoinflation often by expiring against a closed mouth. Our case also showed forced retrograde pneumatic autoinflation by coughing with closed mouth.
The normal anatomic features of Stensen's duct preventing the reflux of air and saliva into the parotid gland are described as follows: first, the diameter of the duct orifice is smaller than that of the duct itself; second, the slit-like duct opening is covered by redundant mucosal folds, which cover the duct orifice when there is increased intraoral pressure; and third, the duct is compressed in its lateral course along the masseter muscle and its passage through the buccinator muscle with increased oral pressure.^4,5,6,7) Anatomic abnormalities, which are believed to contribute to pneumoparotid, include an insufficiency or hypotonia of the buccinators muscle fibers surrounding the papilla, hypertrophy of the masseter muscle, transient mucous plugging causing decreased salivary flow and abnormal dilation of the duct orifice or patulous duct.
In our case, viral parotitis occurred before pneumoparotid. In our thought, this inflammation of parotid gland might have produced and thrust the thick mucus and this could have made the duct opening wider and more ovoid than the normal orifice. Also, local heat produced by parotitis might have cause the hypotonia of the masseter and buccinators muscles around the parotid gland. We thought these were the possible causes of weakening the reflux preventing system in our patient.
The range of normal intraoral pressure is 2 to 3 mm Hg; however, glassblowing and trumpet playing can increase intraoral pressure to 150 mm Hg.⁸⁾ It is not fully understood why some people experience pneumatic insufflation with high intraoral pressures whereas others do not. Only the right-side pneumoparotid developed in our patient because of elevated intraoral pressure due to repeated cough with covering his mouth and weakened Stenson's duct reflux preventing system due to superimposed right parotitis. Many cases reporting pneumoparotid are recurrent or bilateral, but our case presented with a single episode of unilateral pneumoparotid. This is another supporting clue that parotitis could make the parotid more vulnerable to reflux of air.
There have been cases describing pneumoparotid in association with subcutaneous emphysema of the face and neck, pneumomediastinum⁹⁾ and pneumothorax.¹⁰⁾ Most cases¹¹⁾ have been successfully managed through conservative treatment like our case. However, because pneumomediastinum and pneumothorax can be fatal in some patients, patients accompanying these abnormalities must be carefully managed to prevent another complications such as mediastinitis.
In our knowledge, this is the first report of viral parotitis following pneumoparotid in the epidemic area of mumps. We must keep in mind the possibility of the development of pneumoparotid even when usual inflammatory parotitis is confirmed.

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