Other lymphoreticular organs

CHAPTER 14 Other lymphoreticular organs



Edneia Tani, Lambert Skoog



Chapter contents



Introduction

Waldeyer’s ring

Thymus and mediastinum

Spleen

Mucosa associated lymphoid tissue (MALT)

Diagnostic value of FNA in assessment of extranodal lymphoid tissue


The authors gratefully acknowledge the debt to the late T. Löwhagen, whose contribution to the first edition of this chapter provided a substantial basis for the revised editions.




Introduction


Lymph nodes form only part of the immunological system distributed throughout the body. Other organs and anatomical sites also harbour lymphoid tissue which participates in primary and secondary immune responses. The term ‘extranodal lymphoid tissue’ is used to refer to lymphoid tissue situated outside the lymph nodes. This tissue includes organs such as spleen, thymus and the nasopharyngeal lymphoid aggregations known as Waldeyer’s ring. In addition, extranodal lymphoid tissue exists as mucosa associated lymphoid tissue (MALT) in the gastrointestinal tract, lung, salivary gland, thyroid and orbit.1


Inflammation, autoimmune disorders and malignant lymphomas can involve any of the extranodal collections of lymphoid tissue or lymphoreticular organs, as well as lymph nodes. However, in contrast, the extranodal lymphoid tissue is rarely the seat of metastatic tumour spread which is so frequently seen in lymph nodes.


This chapter will consider the main cytological findings in disease processes at the different anatomical sites of extranodal lymphoid tissue, highlighting any contrasting features with the conditions found in lymph nodes.



Waldeyer’s ring


Lymphoid tissue in the tonsils, base of the tongue and epipharynx compose Waldeyer’s ring. These extranodal sites are often affected by inflammatory disorders, but are rarely the target of fine needle aspiration (FNA) sampling. Waldeyer’s ring is a relatively frequent site for B-cell derived non-Hodgkin lymphomas, a high proportion arising particularly in the tonsils. In contrast, T-cell lymphomas and Hodgkin lymphoma are rarely encountered at this site.


All subtypes of B-cell neoplasms can occur in any part of Waldeyer’s ring but follicular lymphomas and diffuse large B-cell lymphomas appear to be the most frequent. At the time of diagnosis, most patients have cervical node involvement as well.


The tonsil and epipharynx may also be the primary sites for poorly differentiated carcinomas. In these cases distinction from large cell lymphomas may pose a problem.



FNA procedure


The aspiration technique is similar to that of most palpable lesions, but an 8 cm long 25 gauge (0.5 mm) needle will be necessary in most cases. Occasionally, a Franzén prostate needle guide is needed to reach targets not otherwise accessible. Aspiration with a 25 gauge needle usually gives sufficient material for both smears and immunological evaluation. Local anaesthesia is seldom required but when needed, it could be administered in spray form.




Cytological findings: Waldeyer’s ring (Figs 14.1, 14.2)


Reactive lymphoid hyperplasia

Reactive lymphoid hyperplasia is common in the lymphoid tissue of Waldeyer’s ring, and is characterised by a spectrum of lymphoid cells ranging from small mature lymphocytes to immunoblasts. In addition, granulocytes, plasma cells and macrophages containing tingible body material are present.


image

Fig. 14.1 Centroblastic lymphoma of tonsil. (A) FNA smear consisting of large centroblasts with round nuclei and thin rim of cytoplasm (MGG). (B) Immunocytochemistry showing positive reactivity for a B-cell marker (CD20) in centroblasts (left) and one mature cell with T-phenotype (right). (C) Monoclonal lambda light chain expression in centroblasts (right) and negative staining for kappa chains (left).


image

Fig. 14.2 Poorly differentiated carcinoma of tonsil with pleomorphic tumour cells in loose clusters (MGG).



Non-Hodgkin lymphomas

The cytological patterns of the different non-Hodgkin lymphomas are identical to those seen in lymph nodes as described in detail in the preceding chapter. Briefly, the smears are composed of a relatively uniform cell population apart from the mixed lymphomas which include neoplastic follicle centre cells as well as some benign lymphocytes. The most common high-grade lymphoma is the diffuse large B-cell lymphoma (Fig. 14.1). The cells have round nuclei with 1–4 small nucleoli often at the nuclear membrane. The cytoplasm is sparse and may contain small vacuoles.



Hodgkin lymphoma

Elderly patients may occasionally present with Hodgkin lymphoma in the tonsil. Akin to the situation in lymph nodes an immunological characterisation is needed to corroborate cytomorphology for a conclusive diagnosis.



Poorly differentiated carcinoma

Poorly differentiated carcinoma cells may superficially mimic those of a diffuse large B-cell lymphoma. However, carcinomas show a tendency to form aggregates in which the individual cells have poorly defined cytoplasm (Fig. 14.2).1 In rare cases, a confident distinction is only possible by immunocytochemistry.



Metastases

Waldeyer’s ring in particular, and also the tonsil, can be the site of metastases. Melanoma, renal cell carcinoma, synovial sarcoma and small cell undifferentiated lung carcinoma are examples of tumours we have seen metastasising to the tonsil.



Immunocytochemistry


In reactive hyperplasia, polytypic B cells predominate. The vast majority of the lymphomas in this area are of B-cell phenotype, with readily detectable light chain restriction. Positive staining for cytokeratin (CK) or epithelial membrane antigen (EMA) will allow identification of an undifferentiated carcinoma. Nasopharyngeal carcinoma may also be LMP EBV positive.



Thymus and mediastinum


The thymus is a lymphoepithelial organ that has a vital role in the development of T cells and natural-killer cells. It lies in the anterior part of the mediastinum and reaches its greatest size in childhood. In old age, the gland is almost indiscernible.


The thymus undergoes hyperplasia in the autoimmune disease myasthenia gravis, and is occasionally affected by primary neoplasms. These include thymomas, neuroendocrine tumours, lymphomas and germ cell tumours which arise in the epithelial, lymphoid or germinal crest tissue, respectively.2


The relative incidence of tumours differs in childhood and adult life. Thus, in childhood, lymphomas account for 50% of the neoplasms, while germ cell and mesenchymal tumours represent 20% each. In adults, thymomas are the most common neoplasm, representing approximately 50% of all primary tumours. Lymphomas are second and germ cell tumours third in frequency with a relative frequency of 25% and 15%, respectively. Carcinoids are rare as thymic tumours and are usually aggressive.


Tumours in the anterior mediastinum, such as thymomas, can be reached by puncture through the sternum or the intercostal space close to the sternum with the help of radiological guidance. However, endoscopic ultrasound-guided FNA cytology via the trachea or oesophagus is preferred and this technique has an excellent performance rate.


Chapter 2 also includes a discussion of mediastinal tumours.



Lymphomas


The thymus appears to be the primary site for two types of lymphoma. The precursor T-cell lymphoblastic subtype occurs predominantly in young males. The second type is the mediastinal large B-cell lymphoma, which shows a predilection for women in the third or fourth decades.3 The tumour cells, which resemble centroblasts or immunoblasts, are of B phenotype and are thought to be of thymic origin. With aggressive chemotherapy this lymphoma has a relatively good prognosis. In addition to these two subtypes almost all other variants of lymphoma can affect the thymus in rare instances.




Cytological findings: lymphomas (Figs 14.3, 14.4)


Precursor T-lymphoblastic lymphoma

The blasts vary in size; most are medium-sized cells with often vacuolated moderately rich basophilic cytoplasm and round to irregular nuclei (Fig. 14.3). The chromatin is fine and nucleoli are inconspicuous. There is usually a high mitotic rate. Eosinophils are common.4–6


image

Fig. 14.3 Lymphoblastic lymphoma of thymus. (A) Aspirate from mediastinum composed of small- to medium-sized blast cells (MGG). (B) Immunocytochemistry shows T-cell lineage with positive staining on the right and no reaction to the B-cell marker on the left (alkaline phosphatase).


image

Fig. 14.4 Large B-cell lymphoma of thymus. (A) The immature tumour cells have irregular nuclei and large cytoplasm (MGG). (B) Immunocytochemistry: B-cell positivity in tumour cells (right) and T-cell positivity in one mature T-cell (left) (alkaline phosphatase).



Mediastinal large B-cell lymphoma

Aspirates show large atypical cells which vary considerably in size and shape (Fig. 14.4). There is usually an admixture of eosinophils and small benign lymphocytes. In addition, there are usually some small sclerotic tissue fragments in the smears. These features may raise suspicion of Hodgkin lymphoma.7 Other tumours to be considered in the differential diagnosis include primary germ cell tumours of the mediastinum and seminoma. Immunophenotyping will be needed for a conclusive diagnosis.



Immunocytochemistry


Precursor T-lymphoblastic lymphoma is a T-cell neoplasm with expression of the lymphoblastic marker terminal deoxynucleotidyl transferase (TdT). There is a variable expression of T-cell markers but CD3 and CD7 can often be detected. The fraction of proliferation cells as analysed by Ki-67 staining is often over 90%.


The mediastinal large B-cell lymphomas express the B-cell associated antigens CD19 and CD20. The tumour cells rarely express surface immunoglobulin. CD30 is often detected as well as CD45. This profile will allow a conclusive diagnosis in most cases.



Germ cell tumours


In the mediastinum, these rare neoplasms are thought to arise in the primordial germinal crest of the thymus. The most common one is the benign teratoma, which accounts for over 80% of germ cell tumours. They often grow to a large size without symptoms and may be cystic. The malignant germ cell tumours such as seminomas, embryonal carcinomas and the rare yolk sac tumour are almost exclusively seen in males in the second and third decade of life.2 In contrast, the choriocarcinoma is more frequent in girls. Most patients present with pain, cough and shortness of breath. In patients with these tumours it is important to exclude metastasis from a primary gonadal neoplasm, which, however, is extremely uncommon.


Teratomas are by definition benign and most patients are cured by resection. Pure seminomas have a favourable prognosis with over 90% 5-year survival. Embryonal carcinoma has a reported long-term survival of around 50%. Patients with choriocarcinoma have a poor prognosis.




Cytological findings: germ cell tumours (Figs 14.5–14.7)


Benign teratoma

Aspirates from benign teratomas may contain stratified squamous epithelium, sebaceous material, hair and a variety of benign cells from all germinal layers.8


image

Fig. 14.5 Mediastinal seminoma. Dispersed fragile cells with poorly defined cytoplasm in typical ‘tigroid’ background (MGG).

Related posts:

  1. New techniques
  2. Salivary glands
  3. Thyroid gland
  4. Lymph nodes

Stay updated, free articles. Join our Telegram channel
Tags:
Jun 8, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Other lymphoreticular organs

Full access? Get Clinical Tree
Get Clinical Tree app for offline access