Brain stones revisited—between a rock and a hard place
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Objectives and methods
Large intracranial calcifications are occasionally encountered in routine computed tomography (CT) scans of the brain. These calcifications, also known as “brain stones”, can be classified according to location and aetiology. Combining imaging findings with relevant clinical history and physical examination can help narrow down the differential diagnosis and may allow confident diagnosis in certain situations.
This article provides a pictorial review illustrating various clinical entities resulting in brain stones.
Based on location, brain stones can be classified as extra- or intra-axial. Extra-axial brain stones comprise tumours and exaggerated physiological calcifications. Intra-axial brain stones can further be classified according to aetiology, namely neoplastic, vascular, infectious, congenital and endocrine/metabolic. Imaging findings combined with essential clinical information can help in narrowing the differential diagnosis, determining disease state and evaluating effect of therapy.
• Based on location, brain stones can be either extra- or intra-axial.
• Extra-axial brain stones comprise tumours and exaggerated physiological calcifications.
• Intra-axial aetiologies include neoplastic, vascular, infectious, congenital and endocrine/metabolic.
• CT scan is the mainstay in identifying and characterising brain stones.
• Certain MRI sequences (gradient echo T2* and susceptibility-weighted imaging) are considered adjunctive.
KeywordsBrain diseases/pathology* Calculi* Calcinosis Computed tomography Diagnosis Differential
Classification of brain stones according to location and aetiopathology
Meningiomas, dural osteomas, calcifying tumours (e.g., craniopharyngiomas), calcifying pseudoneoplasms of the neuraxis (CAPNON), exaggerated physiological calcifications
Oligodendrogliomas, medulloblastoma, germ cell tumours, primitive neuroectodermal tumours (PNET), dysembryonic neuroectodermal tumours (DNET), gangliomas, pilocytic astrocytomas
Cavernous malformations, arteriovenous malformations, dystrophic calcification in chronic infarction, chronic vasculitis, aneurysms
TORCH (toxoplasmosis, rubella, cytomegalovirus, herpes simplex), tuberculosis, parasitic infections (e.g. neurocyticercosis, cerebral hydatid cyst disease)
Sturge-Weber syndrome, tuberous sclerosis, lipomas, neurofibromatosis
Fahr’s syndrome, hypoparathyroidism, pseudohypoparathyroidism, hyperparathyroidism
Tiberin  defined “brain stones” or “cerebral calculi” as general terms referring to “large, solitary or multiple, well-circumscribed bony hard areas of pathological intracerebral calcification”, the aetiopathologies of which were thought to be the end result of chronic, insidious “non-neoplastic space-occupying lesions”. The lack of specific data regarding the amount and configuration of calcium salts that would allow detection by plain x-ray is compounded by the fact that no consensus exists on how histological characteristics of intracranial calcifications explain the appearance of intracranial calcifications on plain x-rays [3, 5, 6]. Similarly, there is no clear cutoff value as to what “large” pertains to in the definition of brain stones. The superiority of CT in detecting macroscopic intracranial calcifications as compared to plain x-rays has resulted in routine visualisation of various forms and sizes of intracranial calcification . Despite the ability of CT to quantify calcification, the subjective designation of intracranial calcifications as brain stones has been considered of less importance lately, although the challenge of reaching a radiological diagnosis on the basis of their presence has remained an intellectual curiosity .
In a historical context, conventional skull x-rays have been most instrumental in identifying brain stones. The use of various projections has helped localise brain stones and, in some instances, narrow the differential diagnosis [6, 8, 9]. The introduction of the Potter-Bucky grid in the 1920s further increased the detection rate of skull x-rays . CT (and especially the multidetector CTs), because of their multiplanar reconstruction (MPR) and 3D reconstruction capabilities, have supplanted the use of skull x-rays in the diagnosis of intracranial pathology. They are also considered to be better than magnetic resonance imaging (MRI) in identifying and characterising intracranial calcification [4, 10], although newer MRI sequences such as gradient echo T2* and susceptibility-weighted imaging have been shown to be promising in detecting intracranial calcification [11, 12, 13]. In certain clinical situations, neurological symptoms have even been shown to correlate better with MRI findings than with the corresponding CT-identified calcifications [14, 15, 16].
Classification of brain stones
As with many other intracranial pathologies, brain stones can be localised and classified as either extra- or intra-axial. Various imaging findings have been found to suggest an extra-axial localisation of brain lesions such as buckling of adjacent white matter, expansion of the ipsilateral subarachnoid space, presence of bony reactions and the “dural tail” sign .
Dural calcifications and ossifications, especially of the falx cerebri, can also appear as “brain stones”. They generally do not have any clinical significance and are often incidental findings during CT scans of the brain . Dural calcifications, which are a result of calcium salt deposition, should not be confused with dural ossifications, which actually involves new bone formation . As the falx is derived from multipotential mesenchymal cells, they may become osteogenic after exposure to friction, haemorrhage or trauma [29, 30]. Ossifications in the falx cerebri are considered to be a rare phenomenon [9, 31, 32]. However, their incidence may be underestimated as it has been shown that a percentage of previously identified dense calcification on conventional radiography and CT may actually possess an outer shell of cortical bone surrounding an inner core of (fatty) bone marrow using modern high-resolution CT and MR imaging [28, 31, 32]. They can range in size from small islands of bone to large bony structures, can involve the entire falx [29, 33] and can be associated with certain endocrine and congenital disorders [30, 33].
Intra-axial aetiologies of calcifications potentially resulting in formation of brain stones comprise a broad range of pathologies that can be subdivided into neoplastic, vascular, infectious, congenital and endocrine/metabolic [2, 8, 18, 34].
Granulomatous infections such as tuberculosis as well as parasitic infections such as neurocysticercosis and cerebral hydatid cyst disease can also result in characteristic intracranial calcifications. Knowledge of a history of travel to endemic areas together with biochemical tests, clinical data and specific imaging findings can often lead to a confident diagnosis. Tuberculosis can result in intracranial calcification in 10–20 % of cases and is usually located supratentorially in adults and infratentorially in children. Calcified tuberculomas can range in size from about a centimetre to several centimetres and can appear as a “broken shell” or a dense centrally located lobulated calcification [6, 10, 44]. Neurocysticercosis is the leading cause of adult-onset seizures in less developed countries, as shown by epidemiological studies, with no consensus on whether the intracranial calcifications are epileptogenic or not [45, 46, 47]. The calcifications represent dead larvae and have the appearance of a dense calcified cyst that sometimes contains a dense eccentric nodule. Lastly, cerebral hydatid disease is an extremely rare cause of intracranial calcification. The lesions are usually single, septated or multilocular and represent the dead parasite [48, 49, 50].
Brain stones are more common than previously thought. Modern imaging modalities allow their identification in a wide range of clinical entities. Computed tomography is the mainstay in identifying and characterising brain stones while certain MRI sequences (gradient echo T2* and susceptibility-weighted imaging) are considered adjunctive. Brain stones may be extra- or intra-axial in location. Extra-axial brain stones comprise tumours and exaggerated physiological calcifications. Intra-axial calcifications can be classified under neoplastic, vascular, infectious, congenital and endocrine/metabolic aetiologies. Imaging findings combined with essential clinical information can help in narrowing the differential diagnosis, determining disease state or evaluating effect of therapy.
The authors declare no conflicts of interest. No funding was received for this work.
Conflict of interest
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