How to obtain adequate biopsy specımen in suspected thymic tumors

Abstract

Pathologic diagnosis of thymic tumors (TTs) can be made by surgical or nonsurgical procedures. About 20% of TTs had been diagnosed by pretreatment biopsy methods while the rest had gone to surgery for diagnosis and treatment. However, in the last two decades there was an increase in pretreatment procedures for optimal management of locally advanced or metastatic TTs. Pretreatment tissue diagnosis of a noninvasive TT is not a standard option but is required if there is suspect or atypical clinical presentation and imaging, an invasive tumor requiring a nonsurgical approach or preoperative chemotherapy or chemo-radiotherapy, strong possibility of lymphoma or unclear differential diagnosis between lymphoma or other solid tumor by imaging studies, or suspicion of a metastatic lesion. In surgical diagnosis anterior mediastinotomy, video-assisted thoracic surgery or mediastinoscopy can be chosen for invasive TTs whereas total resection is performed for small, noninvasive tumors. Nonsurgical diagnosis can be made by transthoracic fine or core needle biopsies (TTFNA, TTCNB), conventional bronchoscopy, endobronchial ultrasonography-guided transbronchial needle aspiration (EBUS-TBNA), endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) or medical thoracoscopy depending on procedural amenability according to tumor extension. TTFNA and TTCNB have been the most frequently used nonsurgical methods. However, there is an upward trend in using conventional bronchoscopy, EBUS-TBNA, EUS-FNA and medical thoracoscopy recently. To increase the diagnostic performance of these procedures in TTs, recommendations are (I) obtaining histologic specimens, (II) combining smears or liquid based cytology preparations and cell blocks, (III) obtaining multiple sufficient samples, (IV) combining histologic and cytologic specimens, (V) performing morphologic, immunohistochemical and molecular analyses on all specimens, (VI) using rapid onsite evaluation for cytologic specimens, (VII) correlating pathologic, clinical and radiologic findings, (VIII) consulting experienced pathologists.

Keywords: Thymoma; biopsy; diagnosis; thymic tumor (TT); transthoracic needle biopsy.

Figure 1

A case of thymoma with myastenia gravis diagnosed and treated by surgery. (A) Thoracic CT section showing noninvasive small mass in the anterior superior mediastinum; (B) histology of the tumor (hematoxylin & eosin, ×100): noninvasive thymoma (type B1); (C) immunostain (Cytokeratin CAM5.2, ×100): noninvasive thymoma (type B1).

Figure 2

Transthoracic fine needle aspiration specimens from a thymoma (type A). The smear cytology is suggestive but not diagnostic for thymoma and cannot differentiate the subtypes. The diagnosis and subtype are confirmed by histopathologic and immunohistochemical examination of the cell blocks. (A) Smear cytology (papanicolaou, ×600): dual population of lymphoid and epithelial cells; (B) cell block (hematoxylin & eosin, ×100): glandular structures and rosettes with no lumen; (C) cell block (CD3 immunostain, ×100): scattered CD3-positive lymphocytes; (D) cell block (cytokeratin immunostain, ×40): keratin-positive epithelial cells.

Figure 3

A case of thymic carcinoma (type B3) with extensive mediastional invasion and pleural effusion. (A) CT-guided transthoracic core needle biopsy procedure using Tru-cut needle, Tru-cut biopsy specimen: (B) tumor islands among connective tissue planes (hematoxylin-eosin, ×40), (C) epithelial atypical cells (hematoxylin-eosin, ×100), (D) specific “chicken wire” staining with pancytokeratin around the epithelial cells (immunohistochemistry, ×100), (E) staining of lymphocytes with CD1a in tumor area and connective tissue stroma: positivity of lymphocytes (ımmunohistochemistry, ×100).