An 11-year-old male presented to the Casualty Department with an anterior mediastinal mass.

A full blood count was performed with the following results:
Hb 98 g/L, WBC 37.5 x 109/L and platelet count 35 x 109/L.

A differential white cell count showed an absolute lymphocytosis with 64% lymphoblasts.

A diagnosis of acute lymphoblastic leukaemia (ALL) was made from the blood film.

Bone marrow and trephine biopsies were performed. (See Figure 1)

A morphological examination of the peripheral blood revealed two populations of lymphoblasts. There were small blasts with a high nuclear to cytoplasmic ratio, dense chromatin pattern and inconspicuous nucleoli and larger heterogeneous blasts with cleaved nuclei, fine chromatin and prominent nucleoli.

The bone marrow biopsy resulted in a dry tap. This is often the case, especially in children. The marrow was densely packed with blast cells and fibrous tissue making aspiration impossible. The trephine revealed a bone marrow packed with blasts.

Cytochemistry and immunophenotyping were performed on the bone marrow. The blasts showed focal positivity with the acid phosphatase stain.

Immunophenotyping showed the following results:
HLA-DR-, CD3-, CD19-, CD117-, CD2+, CD4-, CD5+, CD7+, CD8+, CD34+, TdT+, CD1a+, Cyto3+

These findings were consistent with Precursor T-Cell acute lymphoblastic leukaemia.

Cytogenetics showed 46 XY t(11;14)(p13;q11)

Figure 1 Precursor T-Cell ALL

Approximately eighty percent of childhood acute leukaemias are lymphoblastic of which eighty to eighty five percent have the B-progenitor phenotype. Children with Precursor B-Cell ALL are usually younger children under six years of age.

Ten to fifteen percent of children with acute lymphoblastic leukaemia, usually older children and adolescents, present with Precursor T-Cell ALL.

T-Cell ALL almost invariably presents with a high white cell count and bulky extramedullary disease. The children have a lymphadenopathy, hepatosplenomegaly and an anterior mediastinal thymic mass.

T-Cell ALL may also present with central nervous system (CNS) involvement.

Eighty to eighty five percent of children with B-Cell ALL go into remission and remain relapse-free survivors. T-Cell ALL children usually relapse early into their treatment and are transplanted as soon as remission is achieved.

The patient in this case study had a bone marrow transplant early into the course of his treatment. He remained well for eighteen months. He then presented with increased intracranial pressure, vomiting, headache, papilledema and lethargy. A CSF specimen revealed CNS involvement. (See Figure 2)

Precursor T-Cell ALL

A bone marrow biopsy was performed. The marrow was found to be clear of leukaemia. This is often the case in CNS relapse.

His CNS leukaemia was treated with intrathecal methotrexate however this proved unsuccessful and he died several weeks later.