The mediastinum is the space between the pleural cavities that contains the heart and all chest viscera except lungs. It is bound laterally by parietal pleura, anteriorly by sternum, posteriorly by ribs and paravertebral gutters, superiorly by thoracic inlet and inferiorly by diaphragm¹.The major structures in the mediastinum are heart occupying the middle compartment, oesophagus in posterior compartment, thymus in the anterior compartment. The aortic arch and proximal aorta are located in the superior compartment².

There are various pathologies that can affect the organs within the mediastinum. However, mediastinal masses are encountered very rarely in everyday practice. Lately, the number of asymptomatic patients who present with mediastinal masses on routine X-ray has increased³.Young people are frequently affected but delayed diagnosis is associated with poor prognosis. They pose a diagnostic challenge and hence require clinical, radiological and histopathological correlation to differentiate amongst them. Investigation of the patient with mediastinal mass should follow a logical sequence.³With this information in the background, we report few cases of mediastinal masses encountered in a tertiary care centre which might aid in the differential diagnosis and treatment.

Objectives-

1. To portray the various histopathological types of mediastinal masses that are often encountered in Eastern India.
2. The knowledge about the spectrum of diagnosis not only interests pathologists from academic point of view, but also enables the clinicians to accurately and appropriately treat the case.

MATERIALS AND METHODS

The study was conducted over a period of 12 months from March 2023 to February 2024.

Patients diagnosed with mediastinal masses by radiology and clinical examination were selected. Specimens were either resected completely or obtained by biopsy. They were sent from Cardio-thoracic surgery department to the Department of Pathology along with a duly filled up consent form.

Study group comprised of 30 cases including males, females and children.

Detailed clinical history, investigation reports of the patients were checked and noted.

After gross examination of larger specimen, sections were taken at 1cm intervals and processed. Smaller biopsy specimen was processed in its entirety.

The tissues were stained with haematoxylin and eosin stain.

Some tissues were sent for immunohistochemistry like Glypican-3, CD117, CD15, CD30, TdT, CK19, MDM2, CD34 etc.

RESULTS

The total number of cases was 32. Out of which 23 were males and 9 were females (Table 1).

There were 6 children (below 12 years of age) ,1 adolescent, 25 adults. 5^th decade was the most common age group (21.87%). (Table 2).

The most common type of mediastinal mass was thymoma (31.25%), followed by lymphoma (18.75%), neurofibroma (12.5%) and other rare variants (yolk sac tumour, teratoma, seminoma, malignant peripheral nerve sheath tumour, schwannoma, follicular neoplasm, thymolipoma, atypical lipomatous tumour, solitary fibrous tumour and inflammatory myofibroblastic tumor). (Table 3)

Table 1- Gender distribution

Table 2- Age distribution

Table 3- Histopathological types

PHOTOMICROGHRAPHS:

Figure 1. YOLK SAC TUMOUR. a) reticular pattern. (100x).  b) papillary pattern. (100x). c) endodermal sinus pattern with Schiller Duval body. H&E (400x). d) Glypican-3 positive.

Figure 2. Mature Teratoma. a). Keratin debris, with squamous epithelium and adipose tissue. (100x). b) Respiratory type epithelium, mucous glands, cartilage, adipose tissue. H&E (100x).

Figure.3. SEMINOMA. a) Sheets of tumour cells separated by fibrous septa with lymphocytic infiltrate. H&E. (400x). b) CD117 positive.

Figure.4. CLASSICAL HODGKIN’S LYMPHOMA. (Nodular sclerosis type)-a)Lacunar Hodgkin (RS) cells in a background of lymphocytes and inflammatory cells, seen in nodules separated by collagen bands.  H&E. b) CD15 membranous, cytoplsmic  and paranuclear (golgi) positivity in Reed Sternberg cells  (400x).

Figure 5. BURKITT’S LYMPHOMA- a)starry sky appearance: lymphoid cells interspersed with tangible body macrophages. Giemsa stain. b) Ki-67 index >95%  (400x).

Figure 6. ANAPLASTIC LARGE CELL LYMPHOMA. Lymphoid cells are large, with abundant cytoplasm and pleomorphic, horseshoe shaped nuclei called hallmark cells.  a) H&E. b) CD30 membranous and paranuclear (golgi) positivity. (400x)

Figure 7. THYMOMA B2 type. a)Polygonal neoplastic epithelial cells in cluster (>3 contiguous cells) along with heavy population of immature T cells. Giemsa stain. b) TdT positive immature T cells. (400x)

Figure 8. THYMOMA AB type. a) Foci of spindle cells (type A component) and immature T cells (type B component). H&E. b) CK 19 positive neoplastic spindle shaped epithelial cells. (400x)

Figure 9. MALIGNANT PERIPHERAL NERVE SHEATH TUMOUR. Fascicular growth of uniform spindle cells with hyperchromatic, wavy nuclei, with frequent mitosis. H&E. a) LPF (100x). b) HPF (400x)

Figure 10. SCHWANNOMA. Hypercellular Antoni A areas (with Verocay bodies- nuclear palisading around fibrillary process) and hypocellular Antoni B areas. Figure 11. NEUROFIBROMA. Bland Schwann cells admixed with stromal cells: mast cells, perineural cells, fibroblasts and collagen fibrils. H&E. (100x)

Figure 12. Thymolipoma- Tumour consists of mature adipose tissue with interspersed non-neoplastic thymic tissue. H&E. (100x)

Figure 13. ATYPICAL LIPOMATOUS TUMOUR. a) Adipocytic subtype. Mature adipocytes with varying size and  nuclear atypia in both adipocytes and stromal cells. H&E. (100x) b) MDM2 nuclear immunopositivity. (400x)

Figure 14. SOLITARY FIBROUS TUMOUR. a) Haphazardly arranged spindle to ovoid cells in a collagenous stroma with thin-walled branching blood vessels. H&E. (100x). b) Strong and diffuse expression of CD34. (400x)

Figure 15. INFLAMMATORY MYOFIBROBLASTIC TUMOUR. Loose fascicles of myofibroblastic and fibroblastic spindle cells with inflammatory cell infiltrate of lymphocytes, plasma cells and eosinophils. H&E. (400x)

DISCUSSION

Laurent F et al (1998) found that the most frequent (60%) mediastinal lesions are thymoma, neurogenic tumors and benign cysts. Neurogenic tumors, germ cell neoplasms and foregut cysts represent 80% of childhood lesions, whereas primary thymic neoplasms, thyroid masses and lymphomas are common in adults.⁴ It is consistent with our study where 53.12% of mediastinal masses consist of thymoma and peripheral nerve sheath tumors.

Tomiyana N et al (2009) observed that anterior mediastinal tumor account for 50% of all mediastinal masses including thymoma, teratoma, thyroid disease and lymphoma⁵, quite similar to our study (56.25%).

Duwe BV et al (2005) found that masses of middle mediastinum are typically congenital cysts while those arising in posterior medistinum are often neurogenic tumor.⁶

Usual symptoms at presentation are cough, chest pain, fever and dyspnoea, localising symptoms are secondary to tumor invasion (respiratory compromise, paralysis of limbs, diaphragm or vocal cords, Horner syndrome, superior vena cava syndrome), while systemic symptoms are due to release of excess hormones, antibodies or cytokines.⁷

Sridhar R et al (2021) concluded that 45.2 % of mediastinal lesions are malignant and the masses were commonly located in middle mediastinum⁸, whereas in our study 68.75% were malignant masses.

Maximum number of patients were seen in 3rd decade of life in the study conducted by Aroor AR et al (2014)⁹, whereas our study found 5^th decade (21.87%) to be predominant age group, closely followed by 2^nd (18.75%) and 3^rd decade (18.75%).

Baram A et al (2016) found that male predilection for mediastinal masses was more than female, out of 85 patients 46 were males and 39 were females¹⁰, quite similar to our study with male predominance (71.87%).

CONCLUSION

Although thymoma and lymphoma are the most common types of mediastinal masses, other rare tumours are also encountered, which if not diagnosed and managed early, may have adverse prognosis. Hence, clinical, radiological and histopathological correlation is required for adequate handling of this diagnostic challenge.

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