Benign enlargement of subarachnoid spaces (BESS) is the main cause of pediatric macrocephaly, typically due to
delayed arachnoid villi maturation and reduced CSF absorption. Infants with increasing head circumference above
the 95th percentile may mistakenly be diagnosed with BESS if not correlated with macrocephaly. Age and normal
development are important factors, and BESS often appears around 8 months during routine examinations. Familial
occurrence is common. In BESS, the cortical veins are adjacent to the inner table rather than displaced away
from the inner table, as seen with subdural hematomas.
Differential for pediatric macroencephaly includes CSF spaces (BESS, hydranencephaly, hydrocephalus, choroid plexus neoplasms); blood/vasculature (hemorrhage, vascular malformation); parenchyma (dysplastic megalencephaly, metabolic megalencephaly, intracranial mass, cerebral gigantism, neurocutaneous disorder [NF1, SWS, TS]), and calvarium (skeletal dysplasia, thalassemia major). In pediatric hydrocephalus, consider noncommunicating vs communicating; developmental vs acquired; syndromic vs nonsyndromic; and timeframe.
Radiographics. 2023 May;43(5):e220159. doi: 10.1148/rg.220159.
Differential for pediatric macroencephaly includes CSF spaces (BESS, hydranencephaly, hydrocephalus, choroid plexus neoplasms); blood/vasculature (hemorrhage, vascular malformation); parenchyma (dysplastic megalencephaly, metabolic megalencephaly, intracranial mass, cerebral gigantism, neurocutaneous disorder [NF1, SWS, TS]), and calvarium (skeletal dysplasia, thalassemia major). In pediatric hydrocephalus, consider noncommunicating vs communicating; developmental vs acquired; syndromic vs nonsyndromic; and timeframe.
Radiographics. 2023 May;43(5):e220159. doi: 10.1148/rg.220159.
Placental tissue becomes visible around 10 weeks of gestation, and blood flow can be detected by Doppler
ultrasound at 12-13 weeks. The normal placenta may have thin T2-hypointense septa and becomes more vascular in
the third trimester. The myometrium adjacent to the uteroplacental interface shows a trilaminar appearance,
which may change in late gestation. Myometrial contractions are common and should not be mistaken for pathology.
Placenta accreta spectrum (PAS) disorders are associated with uterine scarring from previous Cesarean sections.
These are some US grayscale findings for PAS. Abnormal placental features include the presence of multiple irregularly shaped hypoechoic spaces called lacunae, which can show turbulent flow. These lacunae are typically located within a lobule or cotyledon and are adjacent to the involved myometrium. Retroplacental clear zone may be lost due to its obliteration or irregularity, but it can be obscured by pressure from a distended bladder or the ultrasound transducer. Myometrial thinning, particularly over the placenta, is associated with prior hysterotomy scars or placental invasion. Placental bulge can occur in areas of myometrial thinning, causing deviation of the uterine serosa and contour deformity. Bladder wall interruption refers to the disruption of the normally echogenic bladder wall, and focal exophytic mass indicates the extension of placental tissue beyond the uterine serosa, often into the bladder.
Color Doppler ultrasound findings include the presence of bridging vessels, which are vessels extending from the placenta through the myometrium and reaching the uterine serosa or nearby structures such as the bladder. Uterovesical hypervascularity is characterized by an increased color Doppler signal between the myometrium and the posterior bladder wall, indicating higher vascular density and tortuosity in that area. Subplacental hypervascularity refers to an increased color Doppler signal in the placental bed, indicating elevated vascular density and tortuosity. Placental lacunae feeder vessels are vessels with high-velocity blood flow originating from the myometrium and extending into the lacunae, causing turbulent flow within those spaces.
The presence of intraplacental dark bands serves as the most sensitive MRI feature for PAS disorders. On T2-weighted images, both the dark bands and blood vessels appear hypointense. However, these can be easily differentiated on balanced SSFP images, where the vessels exhibit T2 hyperintensity while the bands remain T2 hypointense.
Radiographics . 2023 May;43(5):e220090. doi: 10.1148/rg.220090.
Placenta accreta spectrum (PAS) disorders are associated with uterine scarring from previous Cesarean sections.
These are some US grayscale findings for PAS. Abnormal placental features include the presence of multiple irregularly shaped hypoechoic spaces called lacunae, which can show turbulent flow. These lacunae are typically located within a lobule or cotyledon and are adjacent to the involved myometrium. Retroplacental clear zone may be lost due to its obliteration or irregularity, but it can be obscured by pressure from a distended bladder or the ultrasound transducer. Myometrial thinning, particularly over the placenta, is associated with prior hysterotomy scars or placental invasion. Placental bulge can occur in areas of myometrial thinning, causing deviation of the uterine serosa and contour deformity. Bladder wall interruption refers to the disruption of the normally echogenic bladder wall, and focal exophytic mass indicates the extension of placental tissue beyond the uterine serosa, often into the bladder.
Color Doppler ultrasound findings include the presence of bridging vessels, which are vessels extending from the placenta through the myometrium and reaching the uterine serosa or nearby structures such as the bladder. Uterovesical hypervascularity is characterized by an increased color Doppler signal between the myometrium and the posterior bladder wall, indicating higher vascular density and tortuosity in that area. Subplacental hypervascularity refers to an increased color Doppler signal in the placental bed, indicating elevated vascular density and tortuosity. Placental lacunae feeder vessels are vessels with high-velocity blood flow originating from the myometrium and extending into the lacunae, causing turbulent flow within those spaces.
The presence of intraplacental dark bands serves as the most sensitive MRI feature for PAS disorders. On T2-weighted images, both the dark bands and blood vessels appear hypointense. However, these can be easily differentiated on balanced SSFP images, where the vessels exhibit T2 hyperintensity while the bands remain T2 hypointense.
Radiographics . 2023 May;43(5):e220090. doi: 10.1148/rg.220090.
Tissue attenuation in CT is primarily determined by Compton scattering and photoelectric absorption. Compton scattering is more prominent at higher energies and depends on electron density, while photoelectric absorption is dominant at lower energies and is influenced by both atomic number and mass density. Materials with higher atomic numbers, such as iodine and calcium, have a greater likelihood of photoelectric interaction, whereas compounds with lower atomic numbers like soft tissue, water, and fat have a lower probability of this effect.
Different types of single-source hardware systems are used in CT scanning to acquire dual-energy images. One method involves rapid kilovoltage switching, where a single X-ray tube switches between low and high energies, while a single detector captures data from both. Another method uses a dual-layer detector that absorbs different energy photons. Twin-beam dual-energy CT splits the beam into high- and low-energy spectra. Dual-layer scanners allow selecting the dual-energy method after scanning using spectral data.
AJR Am J Roentgenol . 2023 May 17. doi: 10.2214/AJR.23.29244.
Different types of single-source hardware systems are used in CT scanning to acquire dual-energy images. One method involves rapid kilovoltage switching, where a single X-ray tube switches between low and high energies, while a single detector captures data from both. Another method uses a dual-layer detector that absorbs different energy photons. Twin-beam dual-energy CT splits the beam into high- and low-energy spectra. Dual-layer scanners allow selecting the dual-energy method after scanning using spectral data.
AJR Am J Roentgenol . 2023 May 17. doi: 10.2214/AJR.23.29244.