[Mycobacterial spindle cell pseudotumor in children: a clinicopathological study of two cases].

Objective: To study the clinicopathologic features, and the diagnosis and differential diagnosis of mycobacterial spindle cell pseudotumor in children. Methods: The clinical data, histopathological features, immunophenotype and special staining of 2 mycobacterial spindle cell pseudotumors were analyzed. The related literatures were reviewed. Results: The age of the two boys was 11 months and 22 months respectively, but their clinical symptoms became apparent at the age of about 4 months. The lesions involved lymph nodes and skin. The first patient also had fever for more than 4 months. Both patients received anti-inflammatory treatment in the outside hospital, but had no obvious improvements of the symptoms. A tumor resection was performed at the outside hospital. Histologically, mycobacterial spindle cell pseudotumor consisted of bland spindle cells, which formed fascicles, without any obvious atypia and mitoses. The cell nuclei were vesicular, with small nucleoli and abundant cytoplasm in some of the cases. The spindle cells expressed histiocyte-associated markers, such as CD68. The Ki-67 proliferation index was low. The mycobacteria were usually readily highlighted by acid-fast staining, which located in the cytoplasm of proliferative spindle cells. In the first case, there was obstructive jaundice because of the progressive enlargement of live portal lymph nodes and systemic disseminated lesions. The second patient had disease recurrence after only operation, and gradually developed other skin nodules and superficial lymph node enlargement. The high-throughput molecular analysis of the skin biopsy confirmed the diagnosis of mycobacterium tuberculosis. After 11 days of anti-tuberculosis treatment, the patient's condition improved significantly. Conclusions: Mycobacterial spindle cell pseudotumor in children is a very rare benign lesion. It is characterized by spindle-histiocyte proliferation caused by mycobacterium infection. An acid-fast stain appears necessary for confirming the diagnosis.