Radiological review of skull lesions

Insights into Imaging https://doi.org/10.1007/s13244-018-0643-0 PICTORIAL REVIEW Radiological review of skull lesions Carrie K. Gomez 1 & Scott R. Schiffman 1 & Alok A. Bhatt 1 Received: 10 April 2018 / Revised: 17 June 2018 / Accepted: 28 June 2018 # The Author(s) 2018 Abstract Calvarial lesions are often asymptomatic and are usually discovered incidentally during computed tomography or magnetic resonance imaging of the brain. Calvarial lesions can be benign or malignant. Although the majority of skull lesions are benign, it is important to be familiar with their imaging characteristics and to recognise those with malignant features where more aggressive management is needed. Clinical information such as the age of the patient, as well as the patient’s history is fundamental in making the correct diagnosis. In this article, we will review the imaging features of both common and uncommon calvarial lesions, as well as mimics of these lesions found in clinical practice. Teaching Points • Skull lesions are usually discovered incidentally; they can be benign or malignant. • Metastases are the most frequent cause of skull lesions. • Metastatic lesions are most commonly due to breast cancer in adults and neuroblastoma in children. • Multiple myeloma presents as the classic Bpunched out^ lytic lesions on radiographs. • Eosinophilic granuloma is an osteolytic lesion with bevelled edges. Keywords Skull . Calvarial . Benign . Malignant . Lesions Introduction Calvarial lesions are often asymptomatic and are usually discovered incidentally during computed tomography (CT) or magnetic resonance imaging (MRI) of the brain or as part of workup of local clinical symptoms or staging of other diseases [1–6]. Occasionally, they may present as a visible, palpable or symptomatic lump [1, 2, 4]. Clinical parameters such as the age and clinical history are important factors to guide the radiological diagnosis. Calvarial lesions may be benign or malignant; fortunately, benign tumours are the most commonly encountered lesions [1–6]. The skull vault is formed by the frontal, parietal, temporal and occipital bones and parts of the zygoma and sphenoid bone. It is composed of two cortical tables; the * Carrie K. Gomez 1 Department of Imaging Sciences, University of Rochester, 601 Elmwood Avenue, Rochester, NY 14602, USA inner and outer tables, and the diploe or marrow space between them (Fig. 1) [1, 4]. Lesions of the calvarium may originate from the bony structures or may be secondary to invasion of scalp-based lesions or brain-based lesions into the skull vault [1, 4]. The skull base forms the floor of the cranial cavity and, therefore, similar lesions can occur in this region; however, there are lesions that are also specific to this location such as chordoma and chondrosarcoma. Recognition of benign and malignant imaging features is important for the radiological diagnosis [1–6]. In general, benign tumours have well-defined borders with a narrow transition zone; sclerotic margins are frequently present. On the other hand, malignant tumours have poorly defined margins, a wide transition zone, aggressive periosteal reaction and often have a soft tissue component; these lesions cause dramatic bony destruction with intracranial or extracranial extension (Table 1) [1, 4]. Skull lesions can be lytic or sclerotic, single or multiple with varied composition; they may arise from osteogenic, chondrogenic, fibrogenic, vascular and/or other elements of bone (Tables 2 and 3). Insights Imaging Fig. 1 Image depicting the calvarium anatomy (a). The skull is composed of the marrow space (diploe), inner and outer tables. Covering the skull is the scalp which consists of the skin, subcutaneous dense connective tissue, galea aponeurotica and loose connective tissue. The outer table is covered by periosteum. Underneath the calvarium are the meninges comprised of the dura mater, arachnoid mater and pia mater. Diagram of the skull depicts patterns of bone destruction in the skull (b) Calvarial lesions are radiologically evaluated with CT and MRI. CT is the most accurate method for evaluating bone destruction of the inner and outer tables, the lytic or sclerotic nature of the lesion and for the evaluation of mineralised tumour matrix [1–3, 6]. MRI is best to depict marrow involvement of the diploe and to evaluate the associated soft tissue component and invasion of adjacent tissues [1–3, 6]. Plain radiographs play a lesser role, but are useful in the assessment and follow-up of lytic lesions such as multiple myeloma; it may also be the initial modality on which a lesion is found [2, 6]. The differential diagnosis of calvarial lesions is important to decide whether biopsy, surgical intervention or conservative treatment is required for further management [1, 2, 6]. In this article, we will review the imaging characteristics of benign and malignant skull lesions, as well as systemic conditions affecting the skull. In addition, normal variants which may be mistaken for pathology, sometimes called Bpseudolesions^, will also be reviewed. Table 1 Features of benign and malignant lesions Benign Malignant Geographic/sharp margins Moth eaten or permeative bone destruction Wide zone of transition Poorly defined margins Periosteal reaction: aggressive, interrupted Soft tissue component Narrow zone of transition Sclerotic margin Periosteal reaction: solid/uninterrupted No soft tissue component Insights Imaging Table 2 Salient features of benign skull lesions on CT and MRI Skull lesion CT MRI Fibrous dysplasia Typically homogeneously sclerotic with Bground-glass appearance^. Juxta-cortical sclerotic lesion. Variable signal depending on amount of mineralised stroma and fibrous tissue. Most commonly hypointense on T1 and T2. Hypointense T1, variable signal on T2 depending on amount of cortical and trabecular bone. Langerhans cell histiocytosis Lytic lesion with Bbevelled edges^. BButton sequestrum^ may be present. Variable signal, extensive marrow oedema is typically present. Plus enhancement. Osseous venous vascular malformation (formerly haemangioma) Intraosseous meningioma Trabeculations, Bsunburst pattern^. BBunch of grapes^ appearance. Diffuse enhancement. Sclerotic lesion. Hyperostosis. Lytic phase: Bosteoporosis circumscripta^. Mixed phase (lytic and sclerotic): skull vault enlargement; Bcotton-wool^ appearance. Blastic phase: bone thickening and sclerosis. Lytic. Well-demarcated margins. Hypointense T1, variable signal on T2. Osteoma Paget disease Calvarial sarcoidosis (usually multiple) Ossifying fibroma Expansile, lytic lesion or solid lesion with areas of cystic changes. Epidermoid cyst Well-demarcated osteolytic lesion with sclerotic margins. Remodelling and expansion of skull tables. Expansile osteolytic lesion. Can have soft tissue component. Dermoid cyst (typically midline near anterior fontanelle) Benign calvarial lesions Fibrous dysplasia Fibrous dysplasia represents 2. (...truncated)