Spectrum of lytic lesions of the skull: a pictorial essay

Abstract

Lytic lesions of the skull include a wide range of diseases, ranging from benign conditions such as arachnoid granulations or vascular lacunae, to aggressive malignant lesions such as lymphomas or metastases. An early and correct characterisation of the nature of the lesion is, therefore, crucial, in order to achieve a fast and appropriate treatment option. In this review, we present the radiological appearance of the most frequent lytic lesions of the skull, describing findings from different imaging modalities (plain X-rays, CT and MRI), with particular attention to diagnostic clues and differential diagnoses. TEACHING POINTS: • Osteolytic skull lesions may be challenging to diagnose. • Association of different imaging techniques may aid image interpretation. • Clinical information and extensive knowledge of possible differential diagnoses is essential. • Some osteolytic tumours, although benign, may present as locally aggressive lesions. • Malignant lesions require accurate staging, followed by variable treatment approaches.

Keywords: Diagnostic imaging; Neoplasms; Radiologists; Review; Skull.

Fig. 1

Arachnoid granulations (AGs). Axial computed tomography (CT) images with brain (a) and bone (b) windows showing two well-defined, round-shaped lesions with cerebrospinal fluid (CSF) density, protruding into the calvarium along the right transverse sinus

Fig. 2

Venous lacuna (VL). Axial CT image with bone (a) window showing a lytic lesion within the left parasagittal diploic space (arrowhead), confirmed on T2-weighted sequence (b). In a caudal slice, a right parasagittal AG can be depicted (c, d)

Fig. 3

Intradiploic epidermoid cyst (IEC). Axial CT images with soft tissues (a) and bone (b) windows show an occipital hypodense osteolytic lesion with smooth margins and greater involvement of the inner table, extensively demineralised

Fig. 4

IEC. On MR images of the same patient shown in Fig. 3, the lesion appears slightly inhomogeneous, mostly hyperintense on T2w (a) and hypointense on T1w (b) images, without contrast enhancement (c), showing diffusion restriction on b 1000 diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) map (d, e). It causes compression on the confluence of sinuses (sagittal contrast-enhanced T1w image, f). As a consequence, the patient presented with intracranial hypertension symptoms

Fig. 5

Intraosseous haemangioma (IH). Coronal (a) and axial (b) reformats of a CT scan with bone window indicate a left frontal expansive lesion with thin margins and intralesional spicules, radiating from a common centre, which erodes the outer layer of the skull, with relative sparing of the inner table

Fig. 6

Aneurysmal bone cyst (ABC). Axial CT images with brain (a) and bone (b) windows show a left frontal lytic lesion with blood-fluid levels, associated with a diffuse ground-glass modification of the frontal bone, related to the presence of a fibrous dysplasia. Magnetic resonance (MR) examination better depicts the multiloculated lesion, confirming blood-fluid levels on T1w (c), FLAIR (d) and DWI (e) images, and showing enhancement of the capsule and internal septa (f)

Fig. 7

Bone desmoplastic fibroma (DF). Axial CT images with soft tissues (a) and bone (b) windows showing a right parietal lytic lesion without erosion of the inner and outer tables

Fig. 8

DF, same patient shown in Fig. 7. On MRI, the lesion presents a typical low signal intensity on T2w and T1w sequences (a, c), without diffusion restriction on the ADC map (b) or enhancement after contrast administration (d)

Fig. 9

Eosinophilic granuloma (EG). Axial CT images with soft tissues (a) and bone (b) windows showing a right frontal lytic lesion with ill-defined margins extending in the contiguous extracranial soft tissues. Erosion of the inner cranial table is more pronounced than of the outer (“hole within a hole” sign). 18(F) FDG-PET CT examination demonstrates a moderate tracer uptake (c, d)

Fig. 10

EG, same patient shown in Fig. 9. On T1w (a) and T2w (b) images, the lesion appears mildly inhomogeneous, with diffusion restriction on the ADC map (c). MRI allows for an accurate evaluation of the surrounding soft tissues, as well as intracranial extension after contrast administration (d), causing a moderate dural thickening

Fig. 11

Primary lymphoma of the bone. Axial CT images with soft tissues (a) and bone (b) windows highlight the presence of a bone lesion of the squamous portion of the left temporal bone, with lytic permeative pattern, extending to temporal extracranial soft tissues

Fig. 12

Primary lymphoma of the bone, same patient shown in Fig. 11. On MRI, the lesion demonstrates low T2 signal on axial (a) and coronal (b) T2-weighted sequences and extension to the temporal fossa and to the epidural space of the middle cranial fossa. The tumour exhibits homogeneous contrast enhancement; axial T1-weighted before (c) and after (d) contrast administration

Fig. 13

Multiple myeloma (MM). Axial CT images with bone window showing multiple osteolytic lesions varying in shape and size, involving the skull vault and base

Fig. 14

Metastasis. Axial contrast-enhanced CT, with brain (a) and bone (b) windows showing a left parietal lytic, widely necrotic, lesion with intra- and extracranial extension. MRI better depicts extraosseous spread on both intra- and extracranial aspects, with dural displacement and thickening, better seen on coronal T2w image (c). The lesion presents diffusion restriction (d) and enhancement (e, f) of the peripheral solid component. T1w (e) and T1w after contrast administration with fat saturation (f) images