Acquired Multilocular Thymic Cyst
Key Facts
Etiology/Pathogenesis
-
Acquired reactive process resulting from underlying infectious or inflammatory stimulus
Clinical Issues
-
Generally cured by complete surgical excision
-
Rare cases can recur when incompletely excised
-
-
Chest pain
-
Dyspnea
-
Often seen in children with AIDS
Macroscopic Features
-
Large, multilocular cystic structure
-
May show fibrous adhesions to pleura and pericardium
-
3-25 cm in diameter
Microscopic Pathology
-
Cystic spaces lined by flat, cuboidal to squamous epithelium
-
Squamous epithelium may show pseudoepitheliomatous hyperplasia
-
Lining of cysts can be traced to dilated Hassall corpuscles
-
-
Prominent stromal hemorrhage, fibrosis, and chronic inflammation in wall of cysts
-
Prominent granulation tissue and cholesterol cleft granulomas in stroma
-
Prominent lymphoid follicular hyperplasia
-
Residual thymus showing branching, elongated strands of thymic epithelium
TERMINOLOGY
Abbreviations
-
Acquired multilocular thymic cyst (AMTC)
Synonyms
-
Lymphoepithelial thymic cyst
Definitions
-
Acquired reactive process that results in cystic dilatation of thymic epithelium
ETIOLOGY/PATHOGENESIS
Pathogenesis
-
Acquired reactive process resulting from underlying infectious or inflammatory stimulus
CLINICAL ISSUES
Presentation
-
Chest pain
-
Dyspnea
-
Chest fullness
-
Associated with AIDS in children
Treatment
-
Surgical excision
Prognosis
-
Excellent prognosis
-
Generally cured by complete surgical excision
-
Rare cases can recur when incompletely excised
MACROSCOPIC FEATURES
General Features
-
Large, multilocular cystic structure
-
Cysts may contain clear or hemorrhagic fluid
-
May show fibrous adhesions to pleura and pericardium
Sections to Be Submitted
-
At least 1 section per centimeter of greatest diameter
-
Submit all solid areas in the walls of cysts
Size
-
3-25 cm in diameter
MICROSCOPIC PATHOLOGY
Histologic Features
-
Cystic spaces lined by flat, cuboidal to squamous epithelium
-
Squamous epithelium may show pseudoepitheliomatous hyperplasia
-
Lining of cysts can be traced to dilated Hassall corpuscles
-
-
Prominent stromal hemorrhage, fibrosis, and chronic inflammation in wall of cysts
-
Prominent granulation tissue and cholesterol-cleft granulomas in stroma
-
Prominent lymphoid follicular hyperplasia
-
Residual thymus showing branching, elongated strands of thymic epithelium
DIFFERENTIAL DIAGNOSIS
Cystic Hodgkin Lymphoma
-
Microscopic islands containing Reed-Sternberg cells should be present
-
Positive identification of Reed-Sternberg cells with antibodies to CD30/CD15 required for diagnosis of Hodgkin disease
Cystic Seminoma
Cystic Thymoma
-
Solid, confluent areas showing features of thymoma should be present in walls of cyst
-
Identification of keratin(+) cells amidst immature CD1a/CD3(+) thymocytes required for diagnosis of thymoma
-
Cysts may also result from massive dilatation and confluence of perivascular spaces
Cystic Teratoma
-
Heterologous elements should be identified in walls of cyst (i.e., cartilage, glial tissue, squamous or glandular epithelium, etc.)
-
May contain immature neural elements (immature teratoma)
MALT Lymphoma of Thymus
-
Cystic spaces in MALT lymphoma show infiltration of small lymphocytes into epithelial lining of cyst
-
Monotonous population of monocytoid B cells is present surrounding lymphoid follicles in MALT lymphoma
-
Infiltration of Hassall corpuscles by lymphocytes create lymphoepithelial lesions in MALT lymphoma
Thymic Carcinoma
-
Cystic mucoepidermoid carcinoma will show solid areas exhibiting epidermoid features and mucocytes in the walls of cysts
-
Basaloid carcinoma of thymus will show cystic dilatation of tumor cell islands that are lined by atypical, basaloid cells
-
Secondary MTC-like changes can be observed in surrounding, uninvolved thymic parenchyma in any type of thymic carcinoma
DIAGNOSTIC CHECKLIST
Clinically Relevant Pathologic Features
-
Multiple cysts lined by epithelium that is in continuity with cystically dilated Hassall corpuscles
-
Cyst walls show prominent fibrosis and chronic inflammation
-
Many cases also show prominent lymphoid follicular hyperplasia
-
Cases with pseudoepitheliomatous hyperplasia of lining epithelium may be confused for invasive squamous cell carcinoma arising in a cyst
Pathologic Interpretation Pearls
-
Most important feature is to make sure that malignant thymic neoplasm with secondary cystic changes (such as thymoma, lymphoma, or seminoma) has been ruled out by thorough sampling
SELECTED REFERENCES
1. Izumi H et al: Multilocular thymic cyst associated with follicular hyperplasia: clinicopathologic study of 4 resected cases. Hum Pathol. 36(7):841-4, 2005
2. Choi YW et al: Idiopathic multilocular thymic cyst: CT features with clinical and histopathologic correlation. AJR Am J Roentgenol. 177(4):881-5, 2001
3. Chhieng DC et al: Multilocular thymic cyst with follicular lymphoid hyperplasia in a male infected with HIV. A case report with fine needle aspiration cytology. Acta Cytol. 43(6):1119-23, 1999
4. Kontny HU et al: Multilocular thymic cysts in children with human immunodeficiency virus infection: clinical and pathologic aspects. J Pediatr. 131(2):264-70, 1997
5. Mishalani SH et al: Multilocular thymic cyst. A novel thymic lesion associated with human immunodeficiency virus infection. Arch Pathol Lab Med. 119(5):467-70, 1995

Stay updated, free articles. Join our Telegram channel

Full access? Get Clinical Tree

