No abstract

This review examines 197 cases of fibrous hamartoma of infancy (FHI) described in the literature and provides a detailed clinicopathologic analysis of what is known to date of this peculiar lesion of the subcutis and lower dermis. The vast majority of these cases occurred within the first year of life (91%). Twenty-three percent were congenital. There was a predilection for boys with a male/female ratio of 2.4. Males and females had similar anatomic distribution with the most common locations being the axillary region, upper arm, upper trunk, inguinal region, and external genital area. Most cases presented as solitary masses, but four cases of multiple separate synchronous lesions have been reported. Most lesions presented as a painless nodule, sometimes with rapid growth. A few cases had overlying skin changes, including alteration in pigmentation, eccrine gland hyperplasia, and increased hair. No lesions were reported to have familial or syndromic association, or to occur in combination with other hamartomas. Spontaneous regression has not been reported. The treatment of choice is local excision. Even with incomplete excision, FHI has a low recurrence rate. Criteria for histologic diagnosis include the presence of well-defined bundles of dense, uniform, fibrous connective tissue projecting into fat, primitive mesenchyme arranged in nests, concentric whorls or bands, and mature adipose tissue intimately admixed with the other components. Flow-cytometric and conventional cytogenetic studies have not been reported; these may clarify any relationship to other fibroblastic/myofibroblastic proliferations in children, resulting in better classification and terminology of this unique lesion.

Among 3236 pediatric necropsies over 23 years, abnormal position of thymic tissue was recorded in 34 cases. Cardiac anomalies, predominantly those seen in DiGeorge syndrome, were present in 24; 3 had noncardiac anomalies only, 4 had other diseases, and 3 were sudden infant deaths. Mediastinal thymic tissue was absent in 22 cases, small or unilateral in 7, and normal in 5. The maldescended thymic tissue was unilateral in 18, bilateral in 11, and multiple on one or both sides in 5. It was situated near the thyroid gland in 19, lower in the neck in 6, and higher in 9, including 7 medial to the submandibular salivary gland and 1 at the base of the skull. The maldescended tissue approached the size of a normal lobe of thymus in eight and was 2.4 to 0.1 cm in the remainder. Over the same period, in only two cases was no thymic tissue found. Among 68,000 surgical specimens over 40 years, there were 10 cases of ectopic thymus in the neck, including 1 cutaneous and 4 cystic. This frequency of thymic tissue in the neck may explain why lymphoid tissues are sometimes relatively normal in cases of absent mediastinal thymus and behooves a search in the submandibular salivary gland region and higher before diagnosing thymic agenesis.

Forty subdermal fibrous hamartomas of infancy occurred in 29 males and 11 females who were 7 months to 4 years of age at surgery. At least 4 were congenital. The lesions were situated in axilla, chest wall, and breast (17 cases); abdominal wall, inguinal region, and scrotum (8); buttock and lower limb (6); upper limb (4); neck and scalp (3); and low back (2). They were 0.7 to 10 cm, ill defined, and five underwent reexcision, which was curative in all. All had the characteristic mixture of fibrous and adipose tissue and nests of immature mesenchyme in different proportions, and nearly all showed lymphocytes and thick patent capillaries in the mesenchyme. However, the fibrous component varied considerably in amount, pattern, and cellularity, so that lesions that were typical in some areas, in others resembled collagenizing vascular granulation tissue, deep fibrous histiocytoma, or fibromatosis. Those in which adipose tissue predominated were distinguished from fibrolipoma by foci of immature mesenchyme and from lipoblastoma by their lack of a capsule and of a lobular pattern.