Abstract:

Introduction: Costello syndrome is a rare autosomal dominant genetic condition caused by a mutation to the HRAS gene. It is associated with intellectual disability and tumor predisposition. Patients have an approximately 15% lifetime risk of developing malignant tumors such as rhabdomyosarcoma, neuroblastoma, and transitional cell carcinoma. Case presentation: An 18-year-old girl with known diagnosis of Costello syndrome presented to clinic with a large, soft subcutaneous nodule on her posterior scalp for many years. Due to the patient’s nonverbal status, it was unclear if there was associated pain. Given the large size of the nodule and the increased risk of malignant tumors in patients with Costello syndrome, further evaluation was pursued. Ultrasound was non-diagnostic and demonstrated a multiloculated hypoechoic lesion with internal septations, vascularity, and a thick, smooth hyperechoic wall. Excisional biopsy was subsequently performed. The histopathologic examination revealed a circumscribed, moderately cellular spindle cell neoplasm with scattered areas of degenerative cytologic atypia. There was no increased mitotic activity or necrosis. NF-1 staining revealed entrapped axons from the neurofibromatous component. The spindle cells were positive for S-100 protein, CD34, EMA, GLUT-1, and Claudin, consistent with a hybrid nerve sheath tumor (neurofibroma and perineurioma components). Discussion/Conclusion: Our case highlights a rare benign tumor in a patient with Costello syndrome. Other common benign tumors described in these patients include papillomas, calcified epithelioma, fibroid polyps, and osteofibrous dysplasia. Due to an increased risk of malignant tumors, close monitoring is essential in patients with Costello syndrome.

Financial Disclosure:
No current or relevant financial relationships exist.

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Devea De, BS