Fibrous hamartoma of infancy (FHI) is a rare, benign soft tissue growth primarily affecting infants and young children. This condition does not spread to other parts of the body.
Understanding Fibrous Hamartoma of Infancy
FHI is an overgrowth of normal, mature cells, typically found in the affected area but arranged in a disorganized manner. These growths present as firm, solitary lumps or nodules beneath the skin, often poorly defined. They are composed of a triphasic mixture of mature fat cells, primitive spindle-shaped cells, and bland fibroblasts or myofibroblasts, cells involved in tissue repair and structure.
These lesions commonly appear in specific body regions, with the axilla (armpit) being the most frequent site, followed by the shoulder, upper arm, back, thigh, and genital area. While FHI can occur anywhere, hands and feet are less commonly affected. Tumor size varies, typically ranging from 0.5 to 5 cm, though some can be larger.
More than 90% of cases are diagnosed within the first year of life, with approximately 20% being present at birth. While the exact cause remains unknown, FHI is classified by the World Health Organization as a benign fibroblastic and myofibroblastic tumor. It is usually a painless growth, though some cases may present with tenderness.
Diagnosis
Diagnosis of fibrous hamartoma of infancy begins with a thorough clinical examination. The doctor observes the lesion’s appearance, texture, mobility, and size. This initial assessment helps differentiate it from other subcutaneous masses in infants.
Imaging studies, such as ultrasound or magnetic resonance imaging (MRI), are often used to further evaluate the mass. Ultrasound can reveal a heterogeneous, echogenic subcutaneous lesion with intervening hypoechoic portions, sometimes appearing in a serpentine or semicircular pattern. MRI provides detailed views, showing heterogeneous soft tissue masses with interspersed hyperintense fat and hypointense fibrous septations on T1- and T2-weighted images. These techniques help determine the growth’s size, depth, and relationship to surrounding tissues.
A definitive diagnosis of fibrous hamartoma of infancy requires a biopsy. A small tissue sample is surgically removed from the mass and examined under a microscope by a pathologist. Pathological analysis confirms the characteristic triphasic cellular composition: fibroblastic fascicles, mature adipose tissue, and immature mesenchymal cells. This microscopic examination confirms the diagnosis.
Treatment and Outlook
The primary treatment for fibrous hamartoma of infancy is surgical removal of the mass. This excision is performed not only to confirm the diagnosis through pathological examination but also to prevent local recurrence and alleviate any associated symptoms. Complete surgical removal is curative.
The prognosis for infants diagnosed with FHI is excellent following complete surgical excision. While recurrence is possible if the mass is not fully removed, occurring in about 10-15% of cases, re-excision is typically effective in managing these instances. Even with positive margins on pathology, clinically significant recurrence remains uncommon. Regular follow-up appointments are often recommended to monitor the site and ensure there are no signs of recurrence.