Microscopically, BL is characterized by a diffuse infiltrative pattern, and the medium- to small-sized cells are homogenous with round to ovoid nuclei, 1–3 prominent basophilic nucleoli and basophilic cytoplasm that usually contain fat vacuoles. BL is histologically characterized by a “starry sky” appearance, representing scattered macrophages that have phagocytosed cell debris among proliferating lymphoma cells. The malignant cells show a mature B-cell phenotype and are negative for the enzyme deoxy nucleotidyl transferase (TdT). The cells express surface immunoglobulin, most bearing surface immunoglobulin M with either kappa or lambda light chains. Cell markers that are usually present include CD20+, BCL6+, CD10+ and BCL2−. Expression of the proliferation antigen Ki-67 is observed in virtually all the tumour cells. BL/leukemia expresses a characteristic chromosomal translocation, usually t(8:14) or t(8:22) or t(2;8) [10]. Each of these translocations juxtaposes the c-myc oncogene and immunoglobulin locus regulatory elements, resulting in the inappropriate expression of c-myc, a gene involved in cellular proliferation. Cytogenetic evidence of c-myc rearrangement is the gold standard for diagnosis of BL. The 2008 WHO classification eliminated the variant category of “atypical BL,” which had been included in the 2001 classification. Thus, a case with the typical BL phenotype (CD20+, BCL6+, CD10+, BCL2–) and genotype (so-called MYC-simple or MYC/IG in the absence of other major cytogenetic anomalies) may be classified as BL, even if there is some cytological variability in the morphology of the neoplastic cells [6, 9]. For cases in which cytogenetic analysis is not available, the WHO has recommended that the Burkitt-like diagnosis be reserved for lymphoma resembling BL or with more pleomorphism, large cells and a proliferation fraction (i.e. Ki-67[+] of ≥99 %) [11].

These are proliferations of large lymphoid cells of B-cell lineage with nuclei at least twice the size of small lymphocytes [14]. The normal architecture of the nodal or extranodal tissue is diffusely replaced with frequent extension into perinodal soft tissues. The malignant cells express pan-B markers including CD19, CD20, CD22 and CD79a with surface immunoglobulin expression in more than half of the cases [14]. The vast majority of pediatric diffuse large B-cell lymphoma cases have a germinal centre B-cell phenotype, as assessed by immunohistochemical analysis of selected proteins found in normal germinal centre B cells, such as the BCL6 gene product and CD10 [15]. About 20 % of pediatric diffuse large B-cell lymphoma presents as primary mediastinal disease (primary mediastinal B-cell lymphoma.

In lymphoblastic lymphomas, the cells are homogenous with scant cytoplasm, round to oval nuclei, with finely stippled chromatin and inconspicuous nucleoli. Lymphoblastic lymphomas are usually positive for TdT, with more than 75 % having a T-cell immunophenotype and the remainder having a precursor B-cell phenotype [10, 16].

The tumours appear as a proliferation of cohesive large, bizarre, pleomorphic cells with abundant cytoplasm (more than most lymphomas) with eccentric horseshoe-shaped nuclei with multiple or single prominent nucleoli [14]. While the predominant immunophenotype of ALCL is mature T-cell, null-cell disease (i.e. no T-cell, B-cell or NK-cell surface antigen expression) does occur. All ALCL cases are CD30+ and more than 90 % of pediatric ALCL cases have a chromosomal rearrangement involving the ALK gene [17]. The category of ALCL in the 2001 WHO classification included both ALK+ and ALK− tumours and excluded primary cutaneous-ALCL. The 2008 classification concluded that current evidence warranted delineation of ALK+ ALCL as a distinct entity. ALK+ ALCL occurs mainly in pediatric and young age groups, has a better prognosis than ALK− ALCL, and exhibits differences in genetics [18].

This is mostly of a T-cell immunophenotype and typically presents as a mediastinal mass, often with an associated pleural effusion. Large mediastinal masses may manifest as severe respiratory distress resulting from airway compression or swelling of the neck, face and arms due to obstruction of the superior vena cava [10]. Lymphoblastic lymphoma may also affect the liver and spleen although isolated primary involvement of the abdomen is rare [10]. Patients may also present with peripheral lymphadenopathy and infiltration of the skin and soft tissues [13].

ALCL may affect nodal as well as extranodal sites. As much as 70 % of patients present with peripheral lymphadenopathy, the commonest site being cervical. Other sites involved include bones, soft tissue or skin, mediastinum or lungs [13]. The skin is the commonest extranodal site [21]. B symptoms such as fever and weight loss are also common in ALCL but relatively uncommon in other forms of NHL.

Burkitt lymphoma (BL) is characterized by a very short doubling time of 24 h and the interval from initiating or promoting events to diagnosis may be comparatively short. There are three clinico-epidemiologic forms of BL namely endemic, sporadic and HIV-associated types.

The jaw is the most commonly affected site in endemic BL; in high-incidence areas up to 90 % of patients may have clinical or subclinical jaw (radiographic abnormalities) involvement [22]. After the jaw the abdomen is the second commonest site of involvement of endemic BL; intra-abdominal structures are involved in 50–60 % of cases. Some parts of Nigeria like Ibadan have however reported a predominance of abdominal sites above jaw in endemic BL [23]. Other sites affected in the endemic tumour include the orbit, ovaries, retroperitoneal structures, kidneys, omentum, bowel wall and the central nervous system. CNS involvement includes cranial nerve palsies, paraplegia (usually flaccid) and malignant CSF pleocytosis. Only 25 % of patients with cranial nerve palsies have CSF pleocytosis. Invasion of the brain parenchyma is rare. Other sites that may be affected in endemic BL are pleura, endocrine and salivary glands, testes, bone and skin [22].

Unlike endemic BL which peaks at 7 years, a recent study on sporadic BL in the United States has showed two separate peaks among males and females, around the ages 10 and 75 years, and a 3rd peak around the age 40 years among males [24]. Previous reports had indicated that the predominant primary site of sporadic BL was the abdomen [20, 22]. A study in the United States that covered the period 1992–2005 revealed that BL tumours most frequently arose in the lymph nodes (56 %); the abdomen (21 %, primarily in the small or large intestine) is now the second most common site [25]. Other sites of involvement of sporadic BL are bone marrow (14 %, also called Burkitt cell leukemia), the oral cavity and the oropharynx [25]. While central nervous system involvement tends to be more common in endemic BL, bone marrow involvement is more common in the sporadic form.

In Uganda where BL is endemic, the frequency of jaw tumours in HIV-positive children is similar to that in HIV-negative children at presentation [26]. However in addition HIV-positive children presented significantly more often with extra-facial disease (lymphadenopathy 67 %, hepatic masses 51 % and thoracic masses 10 %). HIV-associated BL also present more frequently with advanced stage disease than HIV-negative cases [26].

DLBCL presents similarly to BL with abdominal presentation being common. However, compared to BL patients, children with DLBCL more frequently present with localized disease, focal lesions in liver, spleen, lung and a mediastinal mass. Bone marrow and central nervous system involvement is also less common in DLBCL compared with other NHL entities [27].