Page 404 - Textbook of Pathology, 6th Edition

388 2. White cells: There is leucocytosis reaching its peak in 1- Hassall’s corpuscles are distinctive structures within the
2 days after splenectomy. There is shift-to-left of the myeloid medulla composed of onion skin-like concentrically arranged
cells with appearance of some myelocytes. epithelial cells having central area of keratinisation.
3. Platelets: Within hours after splenectomy, there is rise in Thymocytes are predominantly present in the cortex.
platelet count upto 3-4 times normal. These cells include immature T lymphocytes in the cortex
and mature T lymphocytes in the medulla. Well-developed
SPLENIC RUPTURE B-cell lymphoid follicles with germinal centres are rare in
thymus gland.
The most common cause of splenic rupture or laceration is The main function of the thymus is in the cell-mediated
blunt trauma. The trauma may be direct or indirect. Non- immunity by T-cells and by secretion of thymic hormones
traumatic or spontaneous rupture occurs in an enlarged
1
spleen but almost never in a normal spleen. In acute such as thymopoietin and thymosin-α .
Thymic lesions are associated with diverse conditions
infections, the spleen can enlarge rapidly to 2 to 3 times its which may be immunologic, haematologic or neoplastic.
normal size causing acute splenic enlargement termed acute These can be broadly categorised into thymic hypoplasia and
splenic tumour e.g. in pneumonias, septicaemia, acute agenesis, thymic hyperplasia and thymoma, while thymic
endocarditis etc. Some of the other common causes of involvement in myasthenia gravis is discussed in
spontaneous splenic rupture are splenomegaly due to chronic Chapter 28.
malaria, infectious mononucleosis, typhoid fever, splenic
abscess, thalassaemia and leukaemias. THYMIC HYPOPLASIA AND AGENESIS
SECTION II
Rupture of spleen is an acute surgical emergency due to
rapid blood loss and haemoperitoneum. Sometimes Thymic hypoplasia and agenesis are acquired and congenital
fragments of splenic tissue are autotransplanted within the disorders respectively in which the gland is either unusually
peritoneal cavity and grow into tiny spleens there (splenosis). small or absent. These conditions are various types of
hereditary (primary) immunodeficiency diseases such as
TUMOURS DiGeorge’s syndrome, severe combined immunodeficiency
and reticular dysgenesis. Acquired hypoplasia occurs as an
Primary tumours of the spleen are extremely rare. The ageing phenomenon or may occur in the young due to severe
only notable benign tumours are haemangiomas and stress, malnutrition, irradiation, therapy with cytotoxic drugs
lymphangioma, while examples of primary malignant and glucocorticoids.
neoplasms of haematopoietic system i.e. Hodgkin’s disease
and non-Hodgkin’s lymphomas. Non-haematopoietic THYMIC HYPERPLASIA
tumours of the spleen such as angiosarcoma are rare.
Enlargement of the thymus or failure to involute produces
Secondary tumours occur late in the course of disease thymic hyperplasia. Hyperplasia is usually associated with
and represent haematogenous dissemination of the appearance of lymphoid follicles in the medulla of the thymus
malignant tumour. Splenic metastases appear as multiple and is called thymic follicular hyperplasia. Most common cause
nodules. The most frequent primary sites include: lung, of follicular hyperplasia of the thymus is myasthenia gravis.
breast, prostate, colon and stomach. Rarely, direct extension Less common causes are: Addison’s disease, Graves’ disease,
from an adjacent malignant neoplasm may occur.
rheumatoid arthritis, SLE, scleroderma and cirrhosis of liver.

THYMUS THYMOMA
Haematology and Lymphoreticular Tissues
Most common primary tumour present in the anterosuperior
NORMAL STRUCTURE mediastinum is thymoma. Although thymus is a
lymphoepithelial organ, the term thymoma is used for the
The thymus gland is a complex lymphoreticular organ lying tumour of epithelial origin. Most of the patients are adults.
buried within the mediastinum. At birth, the gland weighs In about half the cases, thymoma remains asymptomatic and
10-35 gm and grows in size upto puberty, following which is accidentally discovered in X-rays. Other patients have
there is progressive involution in the elderly. In the adult, associated conditions like myasthenia gravis or local
thymus weighs 5-10 gm. symptoms such as cough, dyspnoea and chest pain.
The gland consists of right and left encapsulated lobes,
joined together by fibrous connective tissue. Connective MORPHOLOGIC FEATURES. Grossly, the tumour is
tissue septa pass inwards from the capsule and subdivide spherical, measuring 5-10 cm in diameter with an average
the lobe into large number of lobules. The histologic structure weight of 150 gm. Sectioned surface is soft, yellowish,
of the lobule shows outer cortex and inner medulla. Both cortex lobulated and may be either homogeneous or contain cysts
and medulla contain two types of cells: epithelial cells and due to the presence of haemorrhage and necrosis.
lymphocytes (thymocytes). Microscopically, the tumour has a thick fibrous capsule
Epithelial cells are similar throughout the thymus gland. from which extend collagenous septa into the tumour
These cells have elongated cytoplasmic processes forming dividing it into lobules. The histology of lobule shows
network in which thymocytes and macrophages are found.