Version May 2024
INTRODUCTION — A variety of cutaneous and subcutaneous nodules may be detected in the newborn. Most are benign and self-limited, such as cysts, subcutaneous fat necrosis, and certain soft tissue tumors. However, some may be locally aggressive or malignant, or can be a marker for other abnormalities, such as neural tube defects [1].
Cysts and tumors that present at birth or in early infancy are reviewed here. Other benign skin lesions, vesiculopustular and bullous disorders, and vascular and pigmented lesions in the newborn are discussed separately.
●(See "Skin lesions in the newborn and infant".)
●(See "Vesicular, pustular, and bullous lesions in the newborn and infant".)
●(See "Vascular lesions in the newborn".)
●(See "Congenital melanocytic nevi".)
●(See "Subcutaneous fat necrosis of the newborn".)
CYSTS — Common types of cysts include dermoid cysts and epidermoid cysts. Other types, such as branchial cleft or thyroglossal duct cysts, may also occur. (See "Cutaneous developmental anomalies in the newborn and infant".)
Dermoid cysts and sinuses — Dermoid cysts are congenital subcutaneous lesions that are usually distributed along embryonic fusion lines of the facial processes or within the neural axis [2]. The most common locations are overlying the anterior fontanelle, the bregma (junction of the coronal and sagittal sutures), upper lateral region of the forehead, lateral upper eyelid (picture 1), and submental region, although lesions can occur anywhere on the scalp, face, spinal axis, or other body sites [3].
Dermoid cysts are almost always present at birth, although subtle lesions may be noticed later, for example, when trauma causes inflammation (picture 2). They present as slow-growing, asymptomatic, rubbery subcutaneous nodules 1 to 4 cm in diameter that are usually solitary. They are nonpulsatile, noncompressible, nontender masses that appear skin colored or bluish [2]. The skin overlying the cyst appears normal unless a pit or a sinus is present [3].
The characteristic histologic findings include a lining of epidermis and evidence of adnexal structures, such as hair follicles, sebaceous glands, and eccrine and apocrine sweat apparatus. Foci of keratinization and, sometimes, mesodermal skin components may be present. These features distinguish dermoid cysts from epidermoid cysts. The latter typically appear later in life on the trunk and extremities. They generally are intradermal and do not uniformly contain hair follicles and sebaceous glands.
Dermal sinus tracts may connect dermoid cysts to the skin surface or to underlying structures, such as the bone, central nervous system (CNS), or paranasal sinuses. Cutaneous sinuses are 1 to 5 mm in length and may have a small tuft of hair protruding from the orifice [2]. Connections to the CNS are most frequent with midline or nasal dermoid cysts, occurring in approximately 25 percent of cases. There are rare reports of lateral dermoid cysts with intracranial connections [4,5]. A pit or sinus is associated with approximately one-half of nasal dermoid cysts. Midline lesions, most commonly in the lumbosacral region, are often markers of spinal dysraphism, including a tethered cord [6,7].
Sinus tracts to the skin are usually detected when they become infected and drain purulent material. If the sinus or cyst communicates with the CNS, cerebrospinal fluid may drain from the lesion. This connection also allows entry of bacteria and may be detected in a patient presenting with meningitis caused by unusual organisms [8].
Patients with midline lesions should be evaluated with neuroimaging to detect CNS connections or underlying spinal dysraphism [3]. Patients with findings on neuroimaging or other clinical abnormalities should be referred to a neurosurgeon.
Dermoid cysts should be surgically excised because of the risk of associated complications; the timing of excision depends upon the site and any associated findings. The most common complication is infection, including meningitis in lesions that connect to the CNS. In addition, the cysts may adhere to the periosteum or erode underlying skull [3,9-12]. Nasal dermoids typically enlarge, resulting in damage to the nasal bones. Malignant degeneration can occur but is rare.
Thyroglossal duct cysts — Thyroglossal duct cysts are the most common form of congenital neck mass. They represent epithelial remnants of the thyroglossal tract and present characteristically as a midline mass at the level of the thyrohyoid membrane, closely associated with the hyoid bone (picture 3). Affected patients should be referred for surgical excision of the cyst if there is infection or persistent drainage. If the size of the lesion and thyroid function are not problems, they can be followed clinically. (See "Cutaneous developmental anomalies in the newborn and infant", section on 'Thyroglossal duct cysts' and "Thyroglossal duct cyst, thyroglossal duct cyst cancer, and ectopic thyroid".)
Branchial cleft cysts — Branchial cleft cysts usually arise from the first and second branchial arches. They are commonly located anterior to the sternocleidomastoid muscle on the lower third of the lateral neck (picture 4). The cysts often contain lymphoid tissue. Third branchial cleft cysts are found at the head of the clavicles. (See "Differential diagnosis of a neck mass", section on 'Branchial cleft cyst'.)
Epidermoid cysts — Epidermoid cysts, also called epidermal inclusion cysts or epidermal cysts, result when epidermal cells located within the dermis proliferate and do not communicate with the surface. They can arise from occluded pilosebaceous follicles, entrapment of epidermal cells along embryonic lines of closures, or traumatic displacement of epidermal cells into the dermis.
Epidermoid cysts usually develop after puberty, although some present in the newborn period [13]. Examples in newborns include milia, median raphe cysts, and midline anterior neck inclusion cysts (MANIC) [14]. Their histologic appearance may be similar to dermoid cysts, or they may contain stratified squamous epithelium.
SUBCUTANEOUS FAT NECROSIS — Subcutaneous fat necrosis of the newborn (SCFN) is a rare, self-limited panniculitis that affects newborns in the first few weeks of life [15]. It typically affects term or post-term newborns and usually follows perinatal complications, such as birth asphyxia, hypothermia, meconium aspiration syndrome, newborn failure to thrive, forceps delivery, and maternal high blood pressure and/or diabetes [16-18].
Clinical features of SCFN include multiple firm, nontender subcutaneous nodules or large plaques that appear one to four weeks after birth. Commonly affected sites are the cheeks, buttocks, back, and limbs; the overlying skin may be erythematous (picture 5A-B).
SCFN should be differentiated from sclerema neonatorum, which also occurs during the first few months after birth, usually in preterm newborns. It is characterized by the presence of diffuse, waxlike hardening of the skin and subcutaneous adipose tissue, which are bound to the underlying muscle and bone, resulting in respiratory and feeding difficulties and flexion contractures (table 1) [19]. Sclerema neonatorum has become exceedingly rare, likely due to advances in neonatal intensive care [20].
SCFN and sclerema neonatorum are discussed in detail separately. (See "Subcutaneous fat necrosis of the newborn" and "Sclerema neonatorum".)
BENIGN TUMORS — Most soft tissue tumors in newborns and infants are benign [21]. These include hemangiomas and other vascular tumors, fibromatoses, non-Langerhans cell histiocytoses, and cutaneous mastocytosis.
Vascular tumors — Vascular tumors occurring in neonates and infants, including infantile hemangiomas, congenital hemangiomas, tufted angiomas and kaposiform hemangioendotheliomas, and pyogenic granulomas, are discussed separately.
●(See "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications".)
●(See "Tufted angioma, kaposiform hemangioendothelioma (KHE), and Kasabach-Merritt phenomenon (KMP)".)
●(See "Pyogenic granuloma (lobular capillary hemangioma)".)
Infantile myofibromatosis — Infantile myofibromatosis, formerly known as congenital fibromatosis, is the most common fibrous tumor of infancy [22]. In three series, approximately 60 percent of cases were congenital, and 90 percent were detected during the first year of life [23-25]. Infantile myofibromas occur more commonly in boys (60 percent) [25]. In most cases, these tumors are sporadic, but rare familial cases have been described. Both autosomal recessive and autosomal dominant inheritance patterns have been reported [26-28].
Variants in the PDGFRB gene, which encodes the platelet-derived growth factor receptor-beta, have been identified as the cause of most cases of autosomal dominant infantile myofibromatosis [29-31]. Penetrance may be variable [32]. Variants in NOTCH3, the human homolog of the Drosophila melanogaster type I membrane protein Notch3, and in SRF (serum response factor) have been reported, suggesting genetic heterogeneity [33,34]. PDGFRB variants have also been identified in cases of sporadic infantile myofibromatosis [35,36].
Clinical presentation — Infantile myofibromatosis occurs in three forms, solitary (the more frequent type), multicentric, and generalized. In the solitary form, a single lesion affecting the skin or muscle is present, most commonly on the head, neck, or trunk (picture 6A-B). Multiple lesions are present in the multicentric form, which is more likely to be congenital and may affect muscles and bones as well as skin and subcutaneous tissues (picture 7) [24,25,37]. The generalized form is characterized by visceral involvement in addition to skin lesions and is associated with a poor prognosis. The most common sites of visceral involvement are lung, bone, gastrointestinal tract, heart, and liver [38]. PDGFR variants associated with infantile myofibromas may also predispose to cerebral aneurysms [35,39].
The superficial lesions are rubbery and firm, rounded nodules and may be mobile [40]. The deeper lesions are nonmobile. They range in diameter from 1 to 7 cm [24]. In some cases, the overlying skin has a red or purple discoloration that may mimic a hemangioma [40] (see "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications"). The lesions may also be sclerodermoid [25]. Reticulate vascular patches with underlying atrophy have rarely been described and are more common in the multicentric form [25,41]. Skin lesions associated with the generalized form vary; rare cases of atrophic papules and widespread, hypopigmented macules have been reported [42].
Diagnosis — The diagnosis of infantile myofibromatosis is usually made on the basis of clinical features and characteristic histopathology. The histologic appearance is similar in solitary and multiple cutaneous and visceral lesions [43]. There are well-circumscribed masses of spindle-shaped cells staining as fibroblasts or smooth muscle cells, bland necrosis with stippled calcification, and plentiful thin-walled vessels. Atypia is uniformly absent.
Additional evaluation to exclude visceral involvement should be considered. While there are no established guidelines for staging or surveillance, some authors recommend screening all patients (even those with apparent solitary disease) for visceral involvement [31,44,45]. Although radiograph/bone scans, ultrasound, computed tomography (CT), fluorodeoxyglucose-positron emission tomography (FDG-PET), and magnetic resonance imaging (MRI) have all been used effectively to screen for systemic disease [25,45-47], whole-body MRI has gained popularity due to its superior soft tissue resolution [48].
One group suggests a dedicated MRI to delineate the clinically apparent lesion and a rapid whole-body MRI at diagnosis followed by imaging surveillance every three to six months for two years [45]. Tumor tissue should be sequenced for PDGFRB variants, and additional genetic evaluation may be indicated [31]. All patients should be referred for genetic counseling [31]. This has implications for not only the patient but also for family members, as first-degree relatives of patients diagnosed with infantile myofibromatosis or PDGFRB germline mutations should also undergo surveillance [31]. Due to the association of cerebral aneurysms with PDGFRB mutations, a screening brain MRI at age 15 to 18 years can be considered for patients with PDGFRB mutations.
Treatment and prognosis — Solitary lesions are often surgically excised. However, close observation of these tumors may be appropriate in cases without visceral involvement, as lesions in most cases spontaneously involute in one to two years, occasionally leaving residual calcifications or atrophic scars [24,25,37,40].
Patients with visceral involvement must be followed closely due to the higher risk of morbidity and mortality, although in many cases, a strategy of observation may be appropriate. Progressive visceral myofibromas or tumors that affect function or cause local complications due to mass effect are surgically excised or treated with chemotherapy [38,48-50]. Successful targeted therapy with PDGFR-beta tyrosine kinase inhibitors has been reported [39,51-54].
Recurrence of infantile myofibromatosis is unusual but can be delayed into adulthood [32]. Therefore, long-term follow-up is indicated for patients with the multicentric or generalized forms of myofibromatosis [45]. Recurrences can be managed by re-excision or treated with chemotherapy [55].
Though the prognosis is generally excellent, infantile myofibromatosis can rarely be progressive and fatal. Poor outcomes are greatest among infants with the generalized form with extensive visceral involvement (often due to cardiopulmonary or gastrointestinal complications), though rare reports of fatalities occurring in patients with solitary disease also exist [44].
Plaque-like myofibroblastic tumor — Plaque-like myofibroblastic tumor, first described in 2007, is a rare, benign, soft tissue tumor presenting in infants and young children as a firm, irregularly shaped dermal plaque typically located on the middle or lower back, although they can develop in other areas, such as the hips or thighs (picture 8) [56-59]. Lesions are 2 to 8 cm in diameter and reddish to brown in color. The diagnosis is based on the clinical presentation and a skin biopsy. Histologically, the tumor resembles a dermatofibroma, with a relatively well-circumscribed proliferation of spindle cells arranged in short fascicles with thin collagen bundles extending through the entire reticular dermis [56]. On immunohistochemistry, these lesions stain for factor XIIIa and smooth muscle actin, but are CD34-negative, consistent with a myofibroblastic lineage.
The differential diagnosis of plaque-like myofibroblastic tumor includes other dermal tumors, including clustered dermatofibroma, fibrous connective tissue nevus, dermatomyofibroma, and dermatofibroma protuberans (table 2) [60,61]. (See "Skin lesions in the newborn and infant", section on 'Connective tissue nevus' and "Dermatofibrosarcoma protuberans: Epidemiology, pathogenesis, clinical presentation, diagnosis, and staging" and "Overview of benign lesions of the skin".)
Treatment is surgical excision. Local recurrence has been reported [56,62].
Infantile digital fibromatosis — Infantile digital fibroma, also called "recurrent digital fibrous tumor of childhood," is a rare, benign childhood tumor that occurs almost exclusively on the digits [63,64]. It usually develops in the first year of life and typically presents as a firm, reddish-pink or skin-colored, asymptomatic nodule 3 to 35 mm in size located on the dorsolateral aspects of the fingers and toes, characteristically sparing the thumbs and great toes (picture 9) [63]. Tumors may be multiple (picture 10) and, if large, may cause deformity and functional impairment.
The diagnosis is based upon the clinical appearance and the histologic finding of a dermal nonencapsulated proliferation of spindle-shaped myofibroblasts intertwined with coarse collagen fibers, with perpendicular cell fascicles reaching the epidermis. The presence of eosinophilic intracytoplasmic inclusions that stain red with Masson's trichrome is pathognomonic. On immunohistochemistry, tumors consistently express alpha-smooth muscle actin, calponin, and desmin [63].
Because lesions may regress spontaneously over several months to years, observation is a reasonable first-line management strategy [65,66]. Lesions causing functional impairment may require surgical excision to prevent joint deformities. However, rapid recurrence after surgical excision is common [63]. Mohs micrographic surgery has been successfully used in a few cases [67,68].
Other juvenile fibromatoses — Other rare fibromatoses that occur in infancy include infantile desmoid-type fibromatosis, fibromatosis colli (congenital torticollis), fibrous hamartoma of infancy, lipofibromatosis, precalcaneal congenital fibrolipomatous hamartoma, gingival fibromatosis, juvenile hyaline fibromatosis, and infantile systemic fibromatosis [69-74]. (See "Congenital muscular torticollis: Clinical features and diagnosis" and "Soft tissue lesions of the oral cavity in children", section on 'Gingival overgrowth'.)
Juvenile xanthogranuloma — Juvenile xanthogranuloma (JXG) is a benign proliferative disorder of histiocytic cells, a non-Langerhans cell histiocytosis. It typically presents within the first two years of life and, though less common, may be congenital [75]. The most common presentation of JXG is a firm, well-circumscribed, yellow-red tumor that increases in size over the first few months of life (picture 11). Less common presentations include exophytic tumors, agminated lesions over an erythematous patch or plaque, infiltrative plaques, subcutaneous masses, or multiple lesions (picture 12). In a review of 31 congenital cases, systemic involvement occurred in 16, the majority of which had multiple cutaneous lesions [75]. The most common extracutaneous sites of involvement are the eyes, followed by the liver, bone marrow, and lung [75]. JXG is relatively common among children with neurofibromatosis type I [76] and may also be associated with Noonan syndrome [77], a related RASopathy.
The clinical presentation, diagnosis, and management of JXG are discussed in greater detail separately. (See "Juvenile xanthogranuloma (JXG)".)
Cutaneous mastocytosis — Cutaneous mastocytomas are rare lesions composed of mast cells that occur in childhood (picture 13A-B). They may be solitary or multiple. Manipulation of the lesion by rubbing or pressure may trigger mast cell mediator release with resultant flushing and, occasionally, hypotension (Darier's sign). In most cases, the caretakers have noticed this phenomenon and can describe it, without the need to disturb the lesion and induce symptoms. Cutaneous mastocytomas typically regress spontaneously by adolescence. Cutaneous and systemic mastocytosis are discussed separately. (See "Mastocytosis (cutaneous and systemic) in children: Epidemiology, clinical manifestations, evaluation, and diagnosis".)
MALIGNANT TUMORS — Malignant soft tissue tumors that present at birth or in the neonatal period are rare and over 50 percent present in the skin or subcutaneous tissue [78]. Examples include rhabdomyosarcoma, infantile fibrosarcoma (IF), neuroblastoma, and congenital leukemia [79]. IFs and malignant rhabdoid tumors appear most commonly in the first year of life [78].
Rhabdomyosarcoma — Rhabdomyosarcoma is a highly malignant skeletal muscle neoplasm that arises from embryonal mesenchyme. It is the most common soft tissue sarcoma in infants, accounting for one-third of all cases [80]. The primary cutaneous form typically presents as a single firm, subcutaneous nodule that adheres to the skin above and tissue underneath [40]. The overlying skin may be erythematous or shiny, occasionally mimicking a deep hemangioma [81]. An extremely rare neonatal presentation is alveolar rhabdomyosarcoma, a very aggressive tumor that frequently includes multiple skin and subcutaneous metastases [82,83]. (See "Rhabdomyosarcoma in childhood and adolescence: Clinical presentation, diagnostic evaluation, and staging".)
Infantile fibrosarcoma — Infantile fibrosarcoma (IF), also called congenital infantile fibrosarcoma, is a rapidly growing, poorly circumscribed spindle cell tumor of the soft tissues that may present at birth or appear subsequently (picture 14). Approximately 75 percent of patients with IF are diagnosed at less than one year of age [84]. Forty percent of cases are discovered at birth [85]. The tumor typically involves the distal extremities, followed by the trunk, although the head and neck region is affected more frequently in infants than older children [21,84,86]. It is the second most common type of soft tissue sarcoma in infants and the most common occurring on the extremities [80].
Histologically, IF is characterized by spindle cells arranged in interlacing fascicles with a high mitotic rate and positive staining for vimentin. The majority of IFs have a recurrent translocation t(12;15)(p13;q25) that results in a fusion gene involving the neurotrophic tyrosine receptor kinase-3 (NTRK3) gene, called ETV6-NTRK3 (also known as Tel-TRKC) [87-92]. This structural rearrangement results in a tropomyosin receptor kinase (TRK) fusion oncoprotein that drives uninterrupted downstream signaling messages and oncogenic transformation and tumor growth [93-95]. TRK fusions involving the NTRK1, NTRK2, and NTRK3 genes have been identified in a variety of other pediatric mesenchymal tumors but at a lower frequency than in IF [96,97]. (See "TRK fusion-positive cancers and TRK inhibitor therapy", section on 'Prevalence' and "TRK fusion-positive cancers and TRK inhibitor therapy", section on 'Basic biology'.)
Immunohistochemical methods are available to identify TRK fusions in IF and can help to differentiate IF from other pediatric fibromatous tumors [98-100]. (See "TRK fusion-positive cancers and TRK inhibitor therapy", section on 'Testing algorithms'.)
The accurate and timely identification of TRK fusions is of immediate therapeutic importance, given that TRK inhibitions have been shown to have robust and durable activity in TRK fusion-positive solid tumors, such as IF. Larotrectinib, an oral small molecule TRK inhibitor, is approved in the United States and elsewhere for adults and children (ages 28 days to 82 years) with solid tumors that have an NTRK gene fusion without a known acquired resistance mutation, that are metastatic or where surgical resection is likely to result in severe morbidity, and that have no satisfactory alternative treatments or have progressed following treatment. (See "TRK fusion-positive cancers and TRK inhibitor therapy", section on 'Efficacy of first-generation TRK inhibitors'.)
Although locally infiltrative, IF rarely metastasizes and generally has a good prognosis; more than 80 percent are cured [101-103]. However, bleeding and coagulopathy may be significant complications, resulting in high mortality [104]. Although surgical resection is the mainstay of treatment, the surgical approach has evolved over the years from the primary treatment modality to a component of a multidisciplinary approach and from mutilating operations, such as amputation, to more conservative tissue-sparing procedures utilizing initial (neoadjuvant) chemotherapy [84,90,105].
Limited data suggest promise for neoadjuvant use of larotrectinib in pediatric sarcomas, such as IF [106-108]. In a phase 1 trial of larotrectinib, all five pediatric patients with locally advanced, documented TRK fusion sarcomas (three with IF) treated with preoperative larotrectinib were able to undergo successful curative-intent surgical resection, with three achieving complete or near-complete (>98 percent treatment effect) pathologic response [106]. These three patients remained off larotrectinib between 7 and 15 months postoperatively. The remaining two patients who had viable tumors at the time of surgical resection and positive resection margins continued to receive adjuvant larotrectinib, although the duration and long-term outcomes were not reported. All four patients with initially inoperable limb sarcomas were able to undergo limb-sparing surgery. Adverse effects of larotrectinib include low grade increases in liver enzyme levels, decrease in neutrophil count, anemia, and vomiting [107].
While small case series such as this demonstrate the potential promise of neoadjuvant therapy with a TRK inhibitor, the main obstacle to broader use of this approach has been timely, preoperative identification of the presence of an NTRK gene or TRK oncogene fusion. (See "TRK fusion-positive cancers and TRK inhibitor therapy", section on 'Testing algorithms'.)
Other soft tissue sarcomas — Other soft tissue sarcomas occurring in the first year of life include malignant rhabdoid tumors, hemangiopericytoma, the Ewing sarcoma family of tumors, dermatofibrosarcoma protuberans, malignant fibrous histiocytoma, and malignant peripheral nerve sheath tumor [79,80]. (See "Clinical presentation, staging, and prognostic factors of Ewing sarcoma" and "Dermatofibrosarcoma protuberans: Epidemiology, pathogenesis, clinical presentation, diagnosis, and staging".)
Neuroblastoma — Neuroblastoma, the most common malignancy identified at birth, typically presents with an abdominal mass. Metastatic cutaneous lesions are present in approximately one-third of children with congenital neuroblastoma [40]. In one review of 208 neonates with cutaneous metastases, 17 percent were neuroblastoma metastases [109].
Lesions appear as firm, nontender, bluish-red nodules and papules distributed over the entire body ("blueberry muffin baby") and have a distinctive response to rubbing, characterized by central blanching with a surrounding halo of erythema that persists for 30 to 60 minutes [40,110]. The mechanism is thought to be vasoconstriction induced by catecholamine release [111]. (See "Epidemiology, pathogenesis, and pathology of neuroblastoma" and "Clinical presentation, diagnosis, and staging evaluation of neuroblastoma".)
Congenital leukemia — Congenital leukemia is an extremely rare disorder that typically presents at birth with hepatosplenomegaly, lymphadenopathy, central nervous system involvement, petechiae, and ecchymoses [112]. Many affected patients have red/brown or violaceous nodules caused by infiltration of the skin by leukemic cells and known as leukemia cutis (picture 15) [112,113]. The differential diagnosis of this so-called "blueberry muffin baby" appearance includes intrauterine infections, hemolytic diseases, and other tumors.
Rarely, affected infants present with a vesiculopustular eruption [114]. The diagnosis is confirmed by skin biopsy. The prognosis depends on the presence of the associated systemic leukemia [112,115]. Patients with aleukemic leukemia cutis can be managed conservatively.
Congenital self-healing reticulohistiocytosis — Congenital self-healing reticulohistiocytosis (CSHR; Hashimoto-Pritzker disease) is a single-system variant of Langerhans cell histiocytosis with involvement limited to the skin that in most cases regresses spontaneously in weeks to months of onset. (See "Clinical manifestations, pathologic features, and diagnosis of Langerhans cell histiocytosis".)
CSHR is an uncommon disease. However, because of the high rate of spontaneous resolution and lack of clinical recognition, its incidence is likely underestimated [116]. Somatic mutations in various genes have been reported, including multiple in the mitogen-activated protein (MAP) kinase cell-signaling pathway (BRAF-V6000E, HRAS) and in PTEN [117]. Circulating mononuclear cells with the BRAF-V600E mutation are infrequently found in patients with CSHR, whereas they can be identified in the majority of patients with skin and multisystem Langerhans cell histiocytosis [118].
CSHR presents at birth or in the newborn period as solitary (25 percent of cases) or multiple cutaneous nodules that may be located anywhere on the infant (picture 16A-B) [119]. The uninodular form has also been termed "solitary Langerhans cell histiocytoma" (picture 17) [117]. The nodules often centrally ulcerate either before or shortly after birth (picture 18). Vesicles and bullae also have been reported [120]. All lesions heal within a few months, sometimes leaving an atrophic, white scar.
The diagnosis of CSHR is based upon the histopathologic evaluation of a skin biopsy. Histology shows a proliferation of mononuclear cells resembling Langerhans cells with characteristic, abundant eosinophilic cytoplasm and a lobulated, kidney-shaped nucleus. Immunostaining is positive for CD1a, CD4, CD207, and S-100 protein. Staining for E-cadherin, Ki-67, and phosphorylated histone H3 is not helpful in differentiating CSHR from disseminated Langerhans cell histiocytosis with cutaneous involvement [116]. Characteristic features seen on electron microscopy are dense bodies, regularly laminated bodies, and Birbeck granules.
Histopathologic and immunophenotypic features distinguish CSHR from other nodular neonatal lesions. In vesicular or bullous cases, congenital varicella and neonatal herpes simplex virus (HSV) must be excluded. (See "Varicella-zoster infection in the newborn" and "Neonatal herpes simplex virus infection: Clinical features and diagnosis".)
Infants with CSHR should be evaluated for extracutaneous involvement, including a complete blood count, coagulation studies, serum chemistries, liver function tests, urine osmolality, chest and bone radiographs, abdominal ultrasound, and bone marrow biopsy if necessary [121]. (See "Clinical manifestations, pathologic features, and diagnosis of Langerhans cell histiocytosis".)
No treatment is required for CSHR. However, close clinical and laboratory monitoring is important because of the possibility of recurrence or progression [122]. A review of 126 reported cases of CSHR found a recurrence rate of 10 percent (all within the first year of life) and a mortality rate of 3 percent [123]. (See "Clinical manifestations, pathologic features, and diagnosis of Langerhans cell histiocytosis".)
SUMMARY
●Cysts – Common types of cysts include dermoid cysts, thyroglossal duct cysts, branchial cleft cysts, and epidermoid cysts. Dermoid cysts are small (1 to 4 cm in diameter), usually solitary, slow-growing, asymptomatic, rubbery, nontender masses that appear skin-colored or blue; the skin overlying the cyst appears normal unless a pit or a sinus is present (picture 1). They are commonly located over the anterior fontanelle, junction of the coronal and sagittal sutures, upper lateral region of the forehead, lateral upper eyelid, and submental region. (See 'Cysts' above.)
●Subcutaneous fat necrosis – Subcutaneous fat necrosis (SCFN) is a rare condition that typically affects term or post-term newborns in the first few weeks of life, usually following perinatal complications. It is characterized by multiple firm, nontender subcutaneous nodules or large plaques over bony prominences (eg, cheeks, buttocks, back, limbs) (picture 5A). SCFN is discussed in detail separately. (See "Subcutaneous fat necrosis of the newborn".)
●Benign tumors – Most soft tissue tumors in newborns and infants are benign. These include hemangiomas and other vascular tumors, fibromatoses, non-Langerhans cell histiocytoses, and cutaneous mastocytosis (see 'Benign tumors' above):
•Vascular tumors – Vascular tumors occurring in neonates and infants, including infantile hemangiomas, congenital hemangiomas, tufted angiomas and kaposiform hemangioendotheliomas, and pyogenic granulomas, are discussed separately. (See "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications" and "Congenital hemangiomas: Rapidly involuting congenital hemangioma (RICH), noninvoluting congenital hemangioma (NICH), and partially involuting congenital hemangioma (PICH)" and "Tufted angioma, kaposiform hemangioendothelioma (KHE), and Kasabach-Merritt phenomenon (KMP)" and "Pyogenic granuloma (lobular capillary hemangioma)".)
•Infantile myofibromatosis – Infantile myofibromatosis, also known as congenital fibromatosis, is the most common fibrous tumor of infancy. It presents in most cases as a solitary lesion on the head, neck, or trunk (picture 6A-B), but can be multicentric or generalized. The diagnosis is based on a lesion biopsy. (See 'Infantile myofibromatosis' above.)
●Malignant tumors – Malignant tumors affecting the skin and soft tissues of newborns and infants include infantile fibrosarcoma, rhabdomyosarcoma, neuroblastoma, congenital leukemia, and congenital self-healing reticulohistiocytosis (see 'Malignant tumors' above):
•Rhabdomyosarcoma – Rhabdomyosarcoma is a highly malignant skeletal muscle neoplasm and the most common soft tissue sarcoma in infants. The primary cutaneous form typically presents as a single firm subcutaneous nodule that adheres to the skin above and tissue underneath. (See "Rhabdomyosarcoma in childhood and adolescence: Clinical presentation, diagnostic evaluation, and staging".)
•Infantile fibrosarcoma – Infantile fibrosarcoma is the second most common type of soft tissue sarcoma in infants. It presents as a rapidly growing, poorly circumscribed subcutaneous mass, most frequently located on the distal extremities. Although locally infiltrative, these tumors rarely metastasize; however, bleeding and coagulopathy may be life-threatening complications. Evaluation for tropomyosin receptor kinase (TRK) fusions, which are common in infantile fibrosarcoma, is important and can guide management. Larotrectinib, a TRK inhibitor approved for the treatment of NTRK fusion-positive solid tumors in children and adults, has shown promise as neoadjuvant and adjuvant treatment of infantile fibrosarcoma. (See 'Infantile fibrosarcoma' above and "TRK fusion-positive cancers and TRK inhibitor therapy".)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Josie A Pielop, MD, who contributed to an earlier version of this topic review.
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