PTEN hamartoma of the soft tissue: the initial manifestation of an underlying PTEN hamartoma tumor syndrome in a 4-year-old female

A 4-year-old female was referred to pediatric orthopedic surgery for left leg pain and limping for 3 months following a motor vehicle collision. Recently, the patient’s mother had noted left knee swelling and dragging of the left leg when walking. Past medical history was significant for hip dysplasia with slight leg length discrepancy. The patient was otherwise healthy. Physical examination was remarkable for left pre-patellar soft tissue fullness with normal range of motion. There was no warmth or tenderness. Subsequent ultrasound revealed a heterogeneous soft tissue mass superior and medial to the patella with a moderate degree of internal vascularity. MR exhibited a heterogeneous soft tissue mass with heterogeneous signal on both T1- and T2-weighted images centered within the vastus medialis obliquus muscle infiltrating the quadriceps tendon. Excisional biopsy was performed with a histopathologic diagnosis of fibroadipose tissue with anomalous vessels, suggestive of phosphatase and tensin homolog (PTEN) hamartoma of the soft tissue (PHOST). The patient was found to be positive for the PTEN gene mutation on genetic testing. The child was also determined to be macrocephalic, a major criterion for PTEN hamartoma tumor syndrome (PHTS). The geneticist advised the patient to undergo yearly physical examinations and early, routine surveillance for several malignancies occurring with PHTS. This case report presents the ultrasound and MRI appearance of a rare benign tumor typically appearing in pediatric patients. The strong association between PHOST and other soft tissue malignancies and the resulting need for life-long surveillance make PHOST an important pathology to recognize.