Intrathymic cyst: clinical and radiological features in surgically resected cases

Abstract

Aim: To investigate radiological and clinical characteristics of pathologically proven cases of intrathymic cysts.

Materials and methods: The study population consisted of 18 patients (five males, 13 females; median age 56 years) with pathologically confirmed intrathymic cysts who underwent thymectomy and had preoperative chest computed tomography (CT) available for review. The patient demographics, clinical presentation, and preoperative radiological diagnoses were reviewed. CT images were evaluated for shape, contour, location of the cysts and the presence of adjacent thymic tissue, mass effect, calcifications, and septa. The size and CT attenuations of the cysts were measured.

Results: The most common CT features of intrathymic cysts included oval shape (9/18; 50%), smooth contour (12/18; 67%), midline location (11/18; 61%), the absence of visible adjacent thymic tissue (12/18; 67%), and the absence of calcification (16/18; 89%). The mean longest diameter and the longest perpendicular diameter were 25 mm (range 17-49 mm) and 19 mm (range 10-44 mm), respectively. The mean CT attenuation was 38 HU (range 6-62 HU) on contrast-enhanced CT, and was 45 HU (range 26-64 HU) on unenhanced CT (p = 0.41). The CT attenuation was >20 HU in 15 of 18 patients (83%). Preoperative radiological diagnosis included thymoma in 11 patients.

Conclusion: In surgically removed, pathologically proven cases of intrathymic cyst, the CT attenuation was >20 HU in most cases, leading to the preoperative diagnosis of thymoma. Awareness of the spectrum of imaging findings of the entity is essential to improve the diagnostic accuracy and patient management.

Fig. 1

A 47-year-old woman with Wegener’s granulomatosis underwent contrast-enhanced chest CT for evaluation of suspected pulmonary embolism. Axial CT image of the chest at the level of aortic arch demonstrated a well-circumscribed oval-shaped mass (arrow), located in the midline, measuring 55 HU. No visible septa or calcification was noted. Thymic neoplasm was suspected and thymectomy was performed. Histopathological diagnosis was intrathymic cyst.

Fig. 2

A histogram represents the distribution of CT attenuation of intrathymic cysts in the cohort of 18 patients.

Fig. 3

A 79-year-old woman with a history of temporal arteritis and hypothyroidism underwent contrast-enhanced chest CT for evaluation of mediastinal mass incidentally noted on neck CT performed for pulsatile neck mass (which turned out to be a tortuous carotid artery). Axial CT image demonstrated a low-density anterior mediastinal mass (12 HU) abutting the pulmonary arterial trunk with partially calcified wall (arrow). Adjacent thymic tissue was visible on CT (arrowhead).

Fig. 4

A 55 year-old woman with an incidentally noted mediastinal mass on neck CT performed for neck pressure. Contrast-enhanced CT image of the chest at the level of aortic arch demonstrated a round-shaped, well-circumscribed mass measuring 55 HU (arrow). Thymoma was suspected radiologically and surgical resection was performed. Histopathological diagnosis was intrathymic cyst.

Fig. 5

A 58-year-old woman with a history of hypothyroidism underwent MRI for a mediastinal lesion noted incidentally on a neck CT examination performed for dysphagia and throat pain. (a) An oval-shaped lesion abutting the aorta was noted (arrows), which was isointense on T1-weighted image [140 ms repetition time (TR)/2.46 ms echo time], and (b) slightly hyperintense to skeletal muscle on HASTE image (1000 ms TR/101 ms TE). Surgical resection was performed for definitive diagnosis and it was histopathologically confirmed to be intrathymic cyst.

Fig. 5

A 58-year-old woman with a history of hypothyroidism underwent MRI for a mediastinal lesion noted incidentally on a neck CT examination performed for dysphagia and throat pain. (a) An oval-shaped lesion abutting the aorta was noted (arrows), which was isointense on T1-weighted image [140 ms repetition time (TR)/2.46 ms echo time], and (b) slightly hyperintense to skeletal muscle on HASTE image (1000 ms TR/101 ms TE). Surgical resection was performed for definitive diagnosis and it was histopathologically confirmed to be intrathymic cyst.