Case presentation
A 9-years-old girl with the chief complaint of a solitary mass present on her scalp for almost 12 months with no significant past medical history was admitted to hospital. An erythematous lesion with the size of 4.5cm was noted on physical examination. No pruritus or tenderness of lesion was evident. The patient did not complain of fever or weight loss during recent months. Computed tomography scan (CT-scan) of the brain revealed no involvement of skull or brain tissue. Systemic examination further revealed no evidence of mass lesion in other parts of the body. Laboratory evaluations revealed normal findings. Hence, en blocresection was achieved and the lesion referred to laboratory for further pathological study. Microscopic analysis revealed heavy diffuse dermal and subcutaneous infiltration of monomorphous medium-sized mononuclear cells, with fine chromatin, scant cytoplasm, and small nucleoli. Mitotic figures were frequent and tumor cells were observed infiltrating between collagen bundles. The integrity of epidermis remained intact (Figures 1, 2). Based on immunohistochemistry (IHC)analysis, CD99, TdT, and CD79a markers were strongly positive in tumor cells with diffuse pattern. Furthermore, CD45 and CD20 markers were also positive in some of the tumor cells (Figures 3,4). Ki67 marker was positive in approximately 40% of tumor cells (Figure 5). Tumor cells were negative for MNF116, EMA, CK7, CK20, Melan A, HMB45, TTF1, S100, Chromogranin, NSE, CD3, CD56, and desmin. Bone marrow biopsy revealed that the tumor had not involved the marrow and full-body CT-scan and whole body bone scan was devoid of any pathological findings. Therefore, the definitive diagnosis of primary cutaneous lymphoblastic lymphoma of B cell type was concluded. One-year follow-up of the patient after proper treatment revealed normal findings and no trace of recurrence.