Supraclavicular thoracic duct cyst: an unusual neck mass

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Spontaneous cervical thoracic duct cyst is an extremely rare differential diagnosis in patients presenting with painless neck lumps. The terms chylous cyst, thoracic duct cyst and lymphocele of the thoracic duct appear to have been used interchangeably in the literature to refer to cystic collection arising from the lymphatic system. Thoracic duct cysts occur primarily in the mediastinum and few have been reported to arise from the cervical portion of the thoracic duct.
During surgical exploration of any neck mass, it is imperative to keep in mind thoracic duct anatomy and its variations in order to avoid inadvertent damage to the duct causing chylous leak or chylothorax. Here we describe our experience with surgical management of such a case.
A 75‐year‐old man was referred by his general practitioner with a 4‐week history of a left supraclavicular lump. He was asymptomatic and had in fact noticed a slight reduction in size of the mass. There was no history of surgery or trauma to the region. He denies any constitutional symptoms such as fevers, chills or weight loss. Medical co‐morbidities include ischaemic heart disease, atrial fibrillation and peripheral vascular disease.
Examination revealed a soft and non‐tender mass over the left supraclavicular area, clinically suggestive of a lipoma. However, a computed tomographic scan of the neck demonstrated a 4.4 × 3.3 cm lobulated and well‐defined mass in the left supraclavicular region that lay behind the left sternocleidomastoid muscle and lateral to the left internal jugular vein (Fig. 1). There was no lymphadenopathy. The radiologist reported it as a complex cystic lesion containing fluid and fat. A fine‐needle aspirate yielded 4 mL of pink milky fluid that microscopically contained foamy macrophages and occasional lymphocytes.
Magnetic resonance imaging (MRI) to further characterize this lesion was contraindicated in this patient's case due to the presence of a cardiac defibrillator. In view of inconclusive diagnostic findings, decision was made to proceed to surgical exploration.
Intraoperatively the cyst was identified to lie beneath the sternocleidomastoid muscle lateral to the internal jugular vein (Fig. 2). A communication was seen between the cyst and the thoracic duct (Fig. 3). Slicing revealed a cyst containing pink milky fluid and pale soft friable tissue. Histological examination confirmed the presence of a cyst lined by a thin layer of flattened endothelial‐type cells with smooth muscle in the wall. Scattered collections of lymphocytes were present. The overall appearance was in keeping with a thoracic duct cyst.
Spontaneous thoracic duct cysts are exceedingly rare phenomena with only a handful of cases reported in the literature. Of the reported cases, the majority occur in the mediastinal portion of the thoracic duct, with supraclavicular thoracic duct cysts being even rarer entities.
The pathogenesis of cystic dilatations of the terminal thoracic duct remains unclear. It has been postulated that they develop as result of either congenital weakness in the thoracic duct wall or from an acquired degenerative process affecting the structure, possibly related to inflammatory changes.1 Trauma may be another factor that could cause deficiencies in the duct wall.4 If the aetiology is indeed congenital duct wall weakness, then the next question is what causes its outpouching and subsequent collection of lymph at a certain time point. Factors influencing size of cysts and rate of growth remain to be identified. In our case, the patient noticed an enlarging supraclavicular mass over a period of 1 month but also reported spontaneous decrease in its size. Natural history appears variable with some authors reporting slow growth of thoracic duct cysts over many years3 while others reported a more rapid progression over weeks.9 There seems to be no obvious age or gender predisposition to the development of these cysts.
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