Skull Tumors and Scalp Lesions
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Lesions of the scalp and skull in the pediatric population include a wide variety of pathologies including congenital, posttraumatic, vascular, inflammatory, and neoplastic etiologies. While most of the lesions are benign, care should be taken with their work-up to identify those lesions which may be malignant. Surgical indications for these lesions include gross total resection when there is concern for malignancy. Neurosurgical intervention is also indicated for correction of a potential cosmetic deformity as well as biopsy for identification of unknown lesions. When resecting skull lesions, consideration should be given to the possible need for reconstruction of the defect. The most common skull and scalp lesions encountered in a pediatric neurosurgery practice are epidermoid/dermoid cysts and Langerhans cell histiocytosis.
Lesions of the scalp and skull arise from a wide variety of pathologies in the pediatric and adolescent population that differ greatly from lesions found in the adult population. These etiologies include congenital, posttraumatic, vascular, inflammatory, and both benign and malignant neoplasms. While a variety of practitioners including pediatricians, dermatologists, plastic surgeons, general surgeons, and otolaryngologists may be involved in the evaluation of lesions of the scalp and skull, pediatric neurosurgeons are uniquely suited to treat these lesions both with their primary resection and reconstructive procedures. Neurosurgical evaluation becomes even more important when a skull or scalp lesion is found to extend into the parenchyma.
Some form of neuroimaging is recommended for the evaluation of suspicious masses. While most patients typically undergo evaluation with computed tomography (CT) or magnetic resonance imaging (MRI), ultrasound has been shown to be useful not only for initial screening but also for monitoring progression of disease and response to treatment after resection limiting further radiation exposure (Riebel et al. 2008; Kosiak et al. 2013). Because up to one-third of patients evaluated for nontraumatic lumps of the head have some intracranial involvement, neuroimaging with CT or MRI is recommended (Ruge et al. 1988). CT and MRI imaging is complementary. CT is superior in evaluating boney lesions and MRI better for the evaluation of soft tissue. Lesions located near the vertex may be obscured with traditional axial imaging but may be well visualized with thin cut coronal and sagittal slices. Three-dimensional reconstruction may also be useful in order to plan reconstructive strategies pre-operatively. Midline or pedunculated scalp masses should undergo MRI evaluation for assessment of possible intracranial involvement and to determine the relationship between the lesion and the dural sinuses. Occasionally neuroimaging during the evaluation of scalp masses reveals a primarily intracranial process such as a brain tumor or subdural empyema.
Lesions of the Scalp
Superficial lesions that are confined to the dermis are often treated by dermatologists and plastic surgeons, while lesions with subgaleal or cranial involvement will often warrant neurosurgical evaluation. Congenital lesions are more common than true neoplasms. While the majority of scalp lesions in children are benign, the potential for malignant transformation requiring aggressive treatment should not be underestimated. Early detection of small lesions may go unnoticed as the scalp becomes covered with hair. Any pathology that can affect the skin may present with lesions on the scalp.
Of the dermatologic conditions, both nevus sebaceous and congenital compound melanocytic nevi are important to identify because they both have the potential for malignant transformation. Nevus sebaceous are congenital lesions of the sebaceous glands of the scalp, which most commonly transform to basal cell carcinoma but have also been reported associated with squamous cell carcinoma (Turan et al. 2015). Congenital compound melanocytic nevi may occur anywhere on the skin and are associated with melanoma (Skender-Kalnenas et al. 1995). Resection is therefore not just recommended for cosmetic reasons but also imperative to decrease the risk for future malignancy.
Scalp nodules result from a variety of processes in children. One of the most common causes of a scalp nodule is the enlargement of lymph nodes, especially in the postauricular region. These enlarged nodes are typically firm, nontender, and moveable. Lymphadenopathy is common after respiratory infection and typically resolves with no intervention. Posttraumatic lesions, such as periosteal nodules, are also common. These are firm nodules that are affixed to the skull and also tend to resolve spontaneously. They may or may not be associated with a fracture. In general, lesions that are fixed to the skull on palpation and are located in the midline require further evaluation to rule out intracranial extension.
Some scalp nodules may have an associated tuft of hair and are often presumed to be related to dermal sinus tracts. However, they often prove to be heterotopic neural nodules after histologic examination. These malformations are likely within the same developmental continuum as meningoceles, cephaloceles, encephaloceles, and dermal sinus tracts. They are found in the midline and para-midline in the parietal-occipital regions.
Subcutaneous palisading granulomas can present as nonmobile, nontender masses of the scalp. These lesions have been described under various names, but are all characterized by collagen necrosis and chronic inflammatory changes. They occur as multiple lesions that vary in size over time and have been associated with a variety of systemic illness of childhood. Typically there is no association with the development of rheumatologic disease unless the erythrocyte sedimentation rate is elevated (Medlock et al. 1994). The lesions are usually found in the occipital or frontal regions of the scalp.
Neurofibromas of the scalp are often associated with genetic conditions such as Neurofibromatosis type I or less commonly Neurofibromatosis type 2. While usually painless lesions that may only require monitoring, surgery is often considered if lesions become painful. This can occur as lesions near the occipital nerve grow and cause pressure and irritation to the nerve. Surgical resection with biopsy is often sought for rapidly enlarging tumors because malignant transformation is possible. Hemorrhagic nerve sheath tumors have also been reported (Nanni and Lotz 1985).
There are a variety of mesenchymal proliferative disorders of infancy that typically present within the first year of life. These disorders are characterized by initial periods of rapid growth and may involve the scalp, skull, and underlying dura. One such disorder is infantile myofibromatosis. This can occur in either solitary or multicentric forms. The multicentric subtype of the disease often involves the calvarium. If there is noted to be visceral involvement at diagnosis, the outcome is often poor; however, if there is no visceral involvement, spontaneous regression of the lesions have been reported (Da-Biao et al. 2009). Intracranial lesions are quite rare and usually present as large hypervascular retro-orbital or posterior fossa masses originating from the dura and eroding through the skull.
Cranial fasciitis is a rare variant of nodular fasciitis that is considered benign and can be successfully treated with surgery (Oh et al. 2007). The lesions are characterized by a rapidly growing subcutaneous mass often with intracranial or intraorbital extension. It is considered a reactive, nontumoral lesion that is associated with head trauma and histologically composed of mitotically active spindle-shaped cells in a myxoid matrix (Hussein 2008).
Vascular Scalp Lesions
Vascular lesions of the scalp are common in newborn infants. Cutaneous vascular anomalies can be divided into two categories: vascular tumors and vascular malformations (Anomalies 2014). The most common vascular tumors are infantile hemangiomas. These lesions usually progress in the first 6–9 months of life, undergo a programmed cell death, and then involute. They typically occur over the head and neck. Those lesions that persist and have potential to cause lifelong functional or aesthetic issues should be treated. Vascular malformations differ from vascular tumors as they consist of dysmorphic blood vessels and grow in proportion to the child (Elluru 2013). Treatment options are based on the diagnosis, and in the case of infantile hemangiomas, may include a variety of medical and noninvasive options such as propranolol, glucocorticoids, and pulsed dye lasers (Bin et al. 2015).
Arteriovenous malformations (AVM) of the scalp are often referred to as cirsoid aneurysms. They may present as pulsatile, compressible masses. In the case of very young infants, they can present as high output heart failure when the lesions increase in size. Other symptoms associated with AVMs include headaches, tinnitus, and local pain. Most of these lesions are congenital; however, they can also be acquired after trauma.
CT without contrast may not reveal any abnormalities and with contrasted studies may only show enhancement of the scalp. Angiography is often necessary to delineate the arterial feeding arteries and venous draining vessels. Most of the vasculature is supplied extra cranially; however, there may be small contributions from parasitized intracranial vessels. Significant blood loss may occur with operative intervention and care must be taken to avoid scalp necrosis. Even after resection, there are high rates of recurrence. Endovascular treatments for embolization may be useful to reduce the blood flow. Direct puncture embolization methods have been reported as both effective and safe treatment options (Gupta et al. 2008). However, even after obliteration of AVMs with endovascular techniques, surgical resection may still be necessary to resect the residual nidus or remove the mass of embolic material (Munakomi et al. 2015).
Congenital scalp defects occur when the cranial portion of the neural tube fails to close. This can result in a large spectrum of anomalies ranging from incompatible with life anencephaly to small skull defects through which only the cranial meninges herniate. Neural tissue is derived from the ectodermal germ layer when inactivation of the growth factor BMP induces the formation of the neural plate (Yamaguchi and Miura 2013). Absence of inactivation of BMP induces ectoderm to become epidermis. The process by which the neural tube forms from the neural plate is called neurulation. The process begins in the cervical region and proceeds cranially and caudally. The cranial neuropore closes at day 25 of gestation and the posterior neuropore closes at day 28.
Aplasia cutis congenita is a full thickness skin defect. They may occur anywhere on the body, but are most commonly found on the scalp near the midline vertex. Approximately 20% of occurrences are associated with underlying skull defects. Severe cases may also have associated defects in the dura and may present with exposed brain. Most can be treated with split thickness skin grafts (Haq et al. 2010).
Lesions of the Skull
Dermoid and Epidermoid Cysts
Dermoid and epidermoid cysts account for approximately half of the scalp and skull lesions encountered by pediatric neurosurgeons (Gibson and Prayson 2007). Dermoid cysts are more likely to present in young children whereas epidermoid cysts are more often present with older children and young adults. The development of these lesions is associated with disjunction of ectodermal and mesodermal derivatives that became trapped in primitive potential spaces that failed to regress. This process occurs in the third to fifth week of embryogenesis. Because of the embryologic origins of these lesions, up 30% may be associated with communications to the dura.
Epidermoid cysts can have congenital or an acquired mechanism. Acquired lesions can occur after trauma when epidermal tissue becomes implanted in the bone marrow. These are slow growing lesions and usually discovered only after they have grown sufficiently in size. The growth rate is linear and approximates the growth rate of skin. They are classically described as “pearly white” tumors, or “cauliflower shaped,” due to rich contents of cholesterol. They may also have a thick viscous brown content from keratin breakdown similar to dermoids. The main microscopic difference between epidermoids and dermoids is their lack of skin appendages (hair follicles, sebaceous and sweat glands). Epidermoids also tend to have a thinner wall and less reactive fibrosis than dermoids.
Langerhans Cell Histiocytosis
LCH lesions form due to the proliferation of Langerhans cells combined with lymphocytes, eosinophils, and normal histiocytes. There is infiltration of abnormal histiocytes within various tissues, including bone, skin, lung, liver, and lymph nodes. LCH can manifest as a single lesion in the skull or as a multifocal, multisystem disease entity. Poor prognostic factors include young age at diagnosis, hepatosplenomegaly, thrombocytopenia, and polystotic (>3 bones involved) disease (Kilpatrick et al. 1995). Children with biopsy-proven LCH undergo further diagnostic workup including chest radiograph, skeletal survey, and laboratory studies.
Imaging is necessary to assess extent of the lesion(s). Radiographically they appear as well-defined osteolytic lesions. On MRI, these skull lesions are typically isointense at T1-weighted imaging, heterogeneously hyperintense at T2-weighted imaging, and enhance with contrast. They also have evidence of restricted diffusion on DWI. Surgery is indicated for definitive diagnosis and when there is need to alleviate pressure on nearby structures. Systemic disease is treated with chemotherapy.
Unifocal LCH is also referred to as an eosinophilic granuloma. They typically present as a swelling or lump. These lesions can be painful or nontender. Monostotic disease is commonly found in the calvarium in the parietal bone with boys being affected greater than girls. Reviews of pediatric skull lesions have revealed eosinophilic granulomas to be among the most common lesions encountered by pediatric neurosurgeons (Yoon and Park 2008). In unifocal disease, surgical resection is the treatment of choice. Sulfamethoxazole and trimethoprim (Bactrim??) after biopsy has also been shown as an effective alternative to surgery (Alexiou et al. 2009).
Aneurysmal Bone Cysts
Aneurysmal bone cysts (ABC) are vascular, benign, tumor-like lesions of the bone. They typically occur in the metaphysis of long bones with skull lesions being rare. They predominantly occur in children, with the majority of patients less than 20 years old. ABCs can present with varying symptoms depending on location. Lesions of the skull are typically painful and can sometimes put pressure on nearby structures causing cranial nerve palsies, increased intracranial pressure, or seizures. Affected patients often present with painful bony swelling at the site of the lesion. Computed tomography and plain radiographs will demonstrate aneurysmal bone cysts appearing as well defined, expansile lytic lesions with thin sclerotic margins. ABCs are usually primary lesions; however, they can also appear as a secondary solid lesion within an underlying bony abnormality. MRI imaging may show fluid-fluid levels. Cerebral angiography is helpful in identifying feeder vessels. Prior to surgical excision, most patients will undergo endovascular embolization, which will aid in devascularizing the lesion prior to surgery, thereby reducing the risk of bleeding. These lesions should be monitored as rarely there have been reports of conversion into fibrous dysplasia (Arango-Fernandez et al. 2016).
Osteoma, Osteoblastoma, and Osteoid Osteoma
Osteomas are benign, bone forming tumors that grow within bone or on bone. They are slow to progress and often asymptomatic unless their location hinders normal function or movement of nearby structures. Centrally located osteomas typically appear as round, well defined, sclerotic lesions often affecting the outer table (and occasionally the inner table) of the skull. Treatment or surgical resection is only necessary if they are symptomatic; however, large osteomas should be evaluated for a definitive diagnosis.
Osteoid osteomas are benign bone tumors made up of osteoblasts (bone forming cells). They are typically less than 2 cm, whereas osteoblastomas are larger. These lesions usually present in patients <20 years of age affecting males more than females 3:1. They often present as a single, solitary, painful lesion. Aspirin and NSAIDS are effective in providing pain relief adding to the notion there is an inflammatory component to these lesions.
Fibrous dysplasia is a benign disease process whereby normal bone is replaced with fibrous connective tissue. The tissue is abnormal. It is composed of fibroblasts and collagen with woven bone. It may present as monostotic, polyostotic, or in association with McCune-Albright syndrome. McCune-Albright syndrome is characterized by the classic triad of polyostotic fibrous dysplasia, café-au-lait skin macules, and endocrinopathies such as precocious puberty. The process begins in the medullary bone and expands to thin and distort the cortical bone. Fibrous dysplasia is caused by somatic activating mutations in the α subunit of the stimulatory G protein encoded by the gene GNAS (Lee et al. 2012).
Fibrous dysplasia most commonly behaves like a slow indolent growing mass lesion. The development of facial deformities and symptoms from compression of adjacent structures such as the optic nerve, cranial nerve VII, and the middle ear ossicles is usually gradual and insidious. Rarely, fibrous dysplasia can undergo periods of rapid growth and cortical expansion. These periods are less common in young children and pre-pubertal adolescents. Although the disease process can continue into adulthood, progression appears to taper off as patients approach skeletal maturity. Malignant transformation to osteosarcoma has been reported to occur in less than 1% of cases.
CT imaging is the modality of choice to define the anatomy and extent of disease. The most common radiographic characteristic of fibrous dysplasia is a “ground glass” appearance. The bone appears thin and without distinct borders. As patients age, the lesions progress to a mixed radio-dense and radio-lucent appearance. When this radiographic change occurs during puberty, it tends to correspond to a period of increased growth, and therefore, close follow-up is advised.
Management of fibrous dysplasia may be categorized as quiescent (stable with no growth), nonaggressive (slow-growing), or aggressive (rapid growth, with or without pain, paresthesia, pathologic fracture). For lesions in the quiescent phase, observation and monitoring for change is acceptable if there is not significant facial deformity. Fibrous dysplasia, in the nonaggressive phase, allows for watchful waiting until the lesion is in the quiescent phase. If surgery is desired by the patient because of progressive deformity, it becomes important to counsel the patient that repeat surgery may be needed if the lesion regrows after resection. Patients with aggressive and rapidly expanding fibrous dysplasia with new onset pain or neurologic symptoms should undergo surgical evaluation.
Vision loss is the most common neurologic complaint associated with fibrous dysplasia. There is significant controversy regarding the management of fibrous dysplasia when the optic nerve is encased, particularly in patients with normal vision. Concern arises when there is encasement of the optic nerved noted on CT imaging and corresponds to compression of the optic nerve resulting in acute loss of vision. Prophylactic decompression of the optic nerve has been recommended; however, the procedure may result in no improvement of vision or postoperative blindness. For asymptomatic patients, regular ophthalmologic examinations may be reasonable. Visual exam should focus on testing to assess for optic neuropathy. New imaging modalities such as optical coherence tomography may be used to determine the thickness of the retinal nerve fiber layer, which has been found to correlate with visual changes. This modality may be useful in examining young children who cannot undergo visual field examination and may be useful in predicting recovery after surgery.
Subgaleal hematomas are not uncommon in the neonatal population with the majority occurring after a vacuum-assisted delivery. With the evaluation of infants presenting with subgaleal hematomas, it is important to take an accurate and thorough birth history. Gestational age, route of delivery (vaginal, VBAC, primary c-section), and use of forceps or vacuum suction devices are all factors that may contribute hematoma formation at time of delivery. Equally important is pregnancy history and family history. Specifically assess for any history of bleeding disorders. Injury to the brain from subgaleal hematomas is uncommon.
Malignant Skull Tumors
Most malignancies of the scalp and skull in children are from metastatic disease. Primary skull tumors are usually treated with radiation and systemic chemotherapy without surgical resection. The role of surgery has traditionally been reserved for biopsies of unknown lesions and decompression of neural elements. In general their prognosis is poor, but has more recently improved with advances made in systemic therapies. Malignancies that can present with scalp lesions include osteosarcoma, Ewing’s sarcoma, neuroblastoma, leukemia, and lymphoma. While usually metastatic lesions, primary osteosarcoma and Ewing’s sarcoma lesions to the skull have been reported. If resection is undertaken, reconstruction of the calvarium is usually deferred because of concern for poor wound healing secondary to immunosuppression from the expected adjuvant therapy.
Lesions of the scalp and skull consist of a diverse group of diagnoses both malignant and benign. Some lesions may have subtle exam findings while others present with obvious deformities. Indications for surgery include diagnostic, therapeutic and cosmetic. Understanding the differential and workup for these lesions is an important part of a pediatric neurosurgery practice so that decisions regarding surgical management can be made.
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