Page 402 - Textbook of Pathology, 6th Edition

386 cases. The condition is currently regarded as an unusual form
of malignant lymphoma.

SPLEEN
NORMAL STRUCTURE

The spleen is the largest lymphoid organ of the body. Under
normal conditions, the average weight of the spleen is about
150 gm in the adult. Normally, the organ lies well protected
by the 9th, 10th and 11th ribs in the upper left quadrant. The
surface of the spleen is covered by a layer of peritoneum
underneath which the organ is ensheathed by a thin capsule.
From the capsule extend connective tissue trabeculae into the
pulp of the organ and serve as supportive network. Blood
enters the spleen by the splenic artery which divides into
branches that penetrate the spleen via trabeculae. From the
trabeculae arise small branches called central arterioles. Blood
in the central arterioles empties partly into splenic venules
and from there into splenic vein, but largely into vascular
SECTION II
sinuses of the red pulp and thence into the splenic venous
Figure 14.29 Langerhans cell histiocytosis—eosinophilic system.
granuloma. Bone biopsy shows presence of infiltrate by collections of
histiocytes having vesicular nuclei admixed with eosinophils. Grossly, the spleen consists of homogeneous, soft, dark red
mass called the red pulp and long oval grey-white nodules
age. The multifocal lytic bony lesions may develop at any called the white pulp (malpighian bodies).
site. Orbital lesion causes exophthalmos, while involvement Microscopically, the red pulp consists of a network of thin-
of the hypothalamus causes diabetes insipidus. Multiple walled venous sinuses and adjacent blood spaces. The blood
spherical lesions in the lungs are frequently present. Half spaces contain blood cells, lymphocytes and macrophages
the patients have involvement of the liver, spleen and lymph and appear to be arranged in cords called splenic cords or
nodes. cords of Billroth. The white pulp is made up of lymphocytes

Microscopically, the lesions are indistinguishable from surrounding an eccentrically placed arteriole. The
those of unifocal eosinophilic granuloma. periarteriolar lymphocytes are mainly T-cells, while at other
places the lymphocytes have a germinal centre composed
Clinically, the affected children frequently have fever, principally of B-cells surrounded by densely packed
skin lesions, recurrent pneumonitis and other infections. lymphocytes.
Though the condition is benign, it is more disabling than the The spleen is a lymphoreticular organ that performs at
unifocal eosinophilic granuloma. The lesions may resolve least the following four functions:
spontaneously or may require chemotherapy or radiation. 1. Like other lymphoid tissues, it is an organ of the immune
system where B and T lymphocytes multiply and help in
Letterer-Siwe Disease immune responses.
2. The spleen plays an active role in sequestering and
Letterer-Siwe disease is an acute disseminated form of LCH
Haematology and Lymphoreticular Tissues
occurring in infants and children under 2 years of age. The removing normal and abnormal blood cells.
disease is characterised by hepatosplenomegaly, lymph- 3. The vasculature of the spleen plays a role in regulating
adenopathy, thrombocytopenia, anaemia and leucopenia. portal blood flow.
There is generalised hyperplasia of tissue macrophages in 4. Under pathologic conditions, the spleen may become the
various organs. site of extramedullary haematopoiesis.
The spleen is rarely the primary site of disease. Being the
Microscopically, the involved organs contain aggregates largest lymphoreticular organ, it is involved secondarily in
of macrophages which are pleomorphic and show nuclear a wide variety of systemic disorders which manifest most
atypia. The cytoplasm of these cells contains vacuoles and commonly as splenic enlargement (splenomegaly) described
rod-shaped histiocytosis-X bodies. below. A few other systemic involvements such as splenic
infarcts and chronic venous congestion (CVC) of spleen have
Clinically, the child has acute symptoms of fever, skin already been considered in Chapter 5 of General Pathology.
rash, loss of weight, anaemia, bleeding disorders and
enlargement of lymph nodes, liver and spleen. Cystic bony SPLENOMEGALY
lesions may be apparent in the skull, pelvis and long bones. Enlargement of the spleen termed splenomegaly, occurs in a
Intense chemotherapy helps to control Letterer-Siwe disease wide variety of disorders which increase the cellularity and
but intercurrent infections result in fatal outcome in many vascularity of the organ. Many of the causes are exaggerated