What other benign lesions could be considered in a patient presenting with a slow-growing skull lesion and symptoms such as headaches and visual disturbances?

Benign Skull Lesions in the Differential Diagnosis

In a patient presenting with a slow-growing skull lesion accompanied by headaches and visual disturbances, the primary benign considerations include meningioma (most common), vestibular schwannoma, epidermoid cyst, osteoma, fibrous dysplasia, and the rare but important leiomyoma/angioleiomyoma, with histiocytic disorders (Langerhans cell histiocytosis, Erdheim-Chester disease, Rosai-Dorfman disease) requiring exclusion when imaging shows osteolytic features. 1

Most Common Benign Skull Base Lesions

Vestibular Schwannomas and Meningiomas

• Vestibular schwannomas account for 75-90% of cerebellopontine angle (CPA) and internal auditory canal (IAC) tumors, with meningiomas representing 3-5% of these lesions. 1
• These are the most frequently encountered benign lesions in skull base locations and should be the primary considerations before rare entities. 1

Epidermoid Cysts

• Epidermoid tumors are benign lesions that commonly occur in the CPA cistern and can produce trigeminal neuralgia and facial paralysis. 2
• These lesions require differentiation from arachnoid cysts, as treatment differs significantly—epidermoid tumors require surgical excision while arachnoid cysts rarely need intervention. 2
• MRI with diffusion-weighted imaging (DWI) and FLAIR sequences provides accurate diagnosis, showing restricted diffusion that distinguishes epidermoids from arachnoid cysts. 2

Rare but Important Benign Skull Base Lesions

Leiomyomas and Angioleiomyomas

• Skull base leiomyomas (LM) and angioleiomyomas (ALM) are extremely rare benign smooth muscle tumors that present with visual deficits, endocrinopathies (in sellar/suprasellar locations), hearing loss (in IAC/EAC locations), and diplopia or altered facial sensation (in cavernous sinus locations). 1
• These lesions can grow up to 7.7 cm and become locally destructive despite their benign nature. 1
• ALMs most commonly affect the cavernous sinus (n=12 cases), cerebellum/subtentorium (n=4), and sella turcica (n=3), occurring predominantly in patients aged 40-60 years with male predominance. 1
• All IAC locations in the literature review were consistent with ALM pathology rather than LM. 1
• Definitive diagnosis requires pathological examination showing smooth muscle actin (SMA)-positive smooth muscle with CD34-positive endothelial cells. 1
• Gross total resection is the treatment of choice, with excellent outcomes and rare recurrence. 1

Osteomas

• Osteomas are benign bone lesions almost exclusive to the craniofacial area, showing very slow continuous growth even in adulthood. 3
• These lesions are frequently asymptomatic and discovered incidentally on CT or plain radiography. 3
• Radiographically, osteomas appear as radiopaque lesions similar to bone cortex and may cause bone expansion. 3
• Cone beam CT is optimal for assessing relationship to adjacent structures and surgical planning. 3
• Surgical treatment is reserved only for symptomatic lesions, with radical resection being the gold standard. 3

Histiocytic Disorders Presenting as Skull Lesions

Langerhans Cell Histiocytosis (LCH)

• LCH affects bone in 60% of cases, presenting as osteolytic skull lesions that can extend intracranially from skull involvement. 1
• Neurologic involvement occurs in 5% of cases, with characteristic MRI findings including globus pallidus/dentate nucleus T1 hyperintensity and brainstem/cerebellum T2 hyperintensity. 1
• Endocrine involvement occurs in 40-70% of cases, with diabetes insipidus (DI) present in 20-30% and potentially preceding LCH diagnosis by years. 1
• Histopathology shows CD68+, Langerin+, CD1a+ cells, with BRAF V600E mutation present in some cases. 1

Erdheim-Chester Disease (ECD)

• ECD affects bones in 95% of cases with pathognomonic long-bone osteosclerosis at the metadiaphysis, but skull involvement presents with dural and pituitary stalk thickening. 1
• Neurologic involvement occurs in 40% of cases with brainstem/cerebellum masses and cerebral white matter enhancement. 1
• Diabetes insipidus occurs in 40% of ECD cases and may present years before diagnosis. 1
• Histopathology shows CD68+, CD163+, Factor XIIIa+ cells with variable S100 expression. 1

Rosai-Dorfman Disease (RDD)

• RDD affects bone in 15% of cases with cortex-based osteolytic lesions, and presents with isolated dural or parenchymal lesions in 10% of neurologic cases. 1
• Orbital masses occur in 5% of cases, sometimes involving the optic nerve. 1
• Histopathology shows CD163+, S100+ cells that are CD1a and Langerin negative. 1

Other Benign Lesions to Consider

Fibrous Dysplasia

• Fibrous dysplasia is a benign bone lesion that can affect the skull, showing characteristic ground-glass appearance on CT. 4
• MRI provides useful diagnostic information and helps differentiate from osteomyelitis and other lesions. 4

Aneurysmal Bone Cyst

• Aneurysmal bone cysts can present as expansile skull lesions with fluid-fluid levels on MRI, potentially requiring resection when large or at risk for pathological fracture. 4, 5
• These lesions are relatively rare but should be considered in pediatric and young adult populations. 5

Chondroblastoma and Osteoblastoma

• These benign bone tumors can occur in the skull base, with MRI being the modality of choice for evaluation. 4
• Chondroblastoma typically shows characteristic imaging features that aid in diagnosis. 4

Critical Diagnostic Approach

Imaging Strategy

• MRI with gadolinium contrast using thin-section pituitary protocol is the gold standard for evaluating skull base masses with visual symptoms. 6
• CT is complementary for detecting calcification patterns (crucial for craniopharyngioma diagnosis) and bone detail. 6
• Whole-body low-dose CT (WBLD-CT) detects 60% more relevant findings than conventional X-rays and should be obtained to exclude systemic disease. 7

Laboratory Workup

• Complete plasma cell dyscrasia panel (SPEP with SIFE, serum free light chains, quantitative immunoglobulins, 24-hour urine with UPEP and UIFE) must be obtained immediately to exclude multiple myeloma and solitary plasmacytoma. 7
• Comprehensive hormonal screening including thyroid function, morning cortisol/ACTH, prolactin, sex hormones, and GH/IGF-1 should be performed for sellar/suprasellar lesions. 6

Tissue Diagnosis

• Adequate tissue must be obtained for both histology and molecular testing, as integrative diagnosis may require ancillary studies. 7
• Never perform internal fixation of a pathological fracture before obtaining biopsy—this is a critical error that compromises diagnosis and treatment. 7

Common Pitfalls to Avoid

• Do not rely solely on conventional X-rays, as lytic lesions only become visible after >50% trabecular bone loss. 7
• Differentiation between benign and malignant lesions can be challenging, particularly with locally aggressive osteomyelitis that may mimic malignancy. 5
• Clinical history is key—age, symptom duration, and associated systemic symptoms significantly narrow the differential diagnosis. 8, 5
• Rare entities like leiomyomas/angioleiomyomas are often diagnosed only after pathological examination, as they are rarely included in initial differential considerations despite causing significant symptoms. 1