PHACE (posterior fossa malformations, hemangiomas, arterial anomalies, cardiac anomalies, eye anomalies) association has many recognized clinical features. A link between PHACE and non-vascular intracranial lesions has not been well-described. We report three pediatric patients with PHACE and non-vascular intracranial lesions.

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OBJECTIVE: Benign tumors with skeletal muscle differentiation are rare and their characterization in the literature is limited. We present a series of twelve pediatric benign tumors with rhabdomyomatous differentiation including seven rhabdomyomatous mesenchymal hamartomas, four fetal rhabdomyomas, and one benign triton tumor, analyzing myogenic markers as well as clinicopathologic and molecular features. A review of the literature was also performed with an emphasis on myogenic marker expression and correlation with molecular features.
RESULTS: Cases obtained from three tertiary pediatric hospitals were retrospectively reviewed. Eleven of twelve cases expressed myogenin in rare to greater than 15% of cells. Five of nine cases had rare to 70-80% of cells positive for MyoD1. One fetal rhabdomyoma demonstrated homozygous deletions in ZEB2. The benign triton tumor harbored a CTNNB1 mutation. Review of the literature identified 160 pediatric benign tumors with skeletal muscle differentiation of which 9 reported myogenin positivity.
CONCLUSIONS: Myogenin and MyoD1 may be variably expressed in benign lesions with skeletal muscle differentiation. Recognition of key morphologic features remains critical to diagnose these lesions and, in rhabdomyoma, to exclude malignancy. Our series expands the knowledge of the relationship between rhabdomyoma and rhabdomyosarcoma (RMS) by identifying a shared molecular alteration in ZEB2.

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital tumor of the dermal and subcutaneous tissues, often presenting as a papule or a pedunculated or sessile mass at the midline on the head and neck. Although RMH is benign, some cases have reported associations with other congenital and syndromic anomalies. Thus, an accurate diagnosis is important, as an internal or systemic evaluation of the patient may be warranted. We report a case of a solitary RMH on the midline upper chest in a healthy 15-year-old girl.

Smooth muscle hamartoma (SMH) and striated muscle hamartoma (STH) are anomalous proliferations of smooth muscle or striated muscle, respectively, in anatomic sites where these tissues are normally present. To date, only limited cases have been reported describing these lesions. In this study, we sought to characterize the clinicopathologic features of both SMH and STH. A total of 27 cases of SMH and 12 cases of STH from 1990 to 2020 were identified. SMH cases had a slight male predominance (63%) and a mean age of presentation of 20 years (range: 4 months-91 years), with a mean size of 9.3 mm (±13.3). In contrast, STH were equally distributed in gender, with a mean age of presentation of 40 years (range: 3 months-66 years) and a mean size of 5.7 mm (±3.6). SMH were more commonly located in the torso and extremities (70%) and STH in the head and neck area (92%). One case of SMH recurred after 1.1 years and in the initial diagnosis the lesion was present at the tissue edge. None of the cases of STH had a recurrence. We present the largest cohort of SMH and STH, and report the first case of a recurrent SMH, suggesting the importance of obtaining a clean margin for these lesions.

OBJECTIVE: The pathogenesis of infantile hemangiomas (IH), PHACE, and LUMBAR syndromes remains unknown. We aim to describe histopathologic features of midline anomalies associated with IH, including patients with PHACE and LUMBAR syndromes.
METHODS: A multicenter retrospective chart review was performed to identify patients with IH, PHACE, and LUMBAR syndrome with histopathologic specimens from sternal or midline anomalies. A total of 18 midline lesions from 13 patients were included. Out of 18, 14 midline lesions underwent both histopathologic and clinical review. Three hamartoma-like chin plaques and one supraumbilical raphe underwent only clinical review.
RESULTS: All 13 patients had midline lesions and IH. Histopathologic diagnoses were as follows: rhabdomyomatous mesenchymal hamartoma (3), folliculosebaceous cystic hamartoma (1), fibroepithelial polyp (1), verrucous epidermal hyperplasia with vascular proliferation and fibroplasia (1), congenital midline cervical cleft (1), pericardium with fibrosis (1), fibrous components with increased collagen (1), atrophic skin/membrane (3), angiolipomatous mass with neural components (1), and lipomatous mass (1). Due to the retrospective nature of this study, it was not possible to obtain pathology slides for all midline lesions that had previously been biopsied or resected. We show clinically and histopathologically a new association between PHACE syndrome and rhabdomyomatous mesenchymal hamartoma (RMH), in addition to demonstrating the association between PHACE syndrome and chin hamartomas. We also display histopathologic findings seen in midline lesions resected from LUMBAR patients.
CONCLUSIONS: Rhabdomyomatous mesenchymal hamartoma is thought to be related to aberrations of mesenchymal cells during development; therefore, this may provide clues to the pathogenesis of IH and related syndromes.

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The spectrum of clinical presentations in pediatric skin and soft-tissue lesions often makes diagnosis challenging. Delays in diagnosis and subsequent treatment can be life threatening, and they can subject patients to more complicated reconstruction. This retrospective case series reviews the presentation, management, and current literature on eight pediatric skin and soft-tissue lesions. For rare lesions and those with unclear pathology, a multidisciplinary approach is strongly advocated for optimal management.