6 Trauma and Hemorrhage



10.1055/b-0036-138079

6 Trauma and Hemorrhage



6.1 Introduction


Traumatic head injuries are a common occurrence, with an incidence of up to 1.7 million per year in the United States as of 2014. 1 ,? 2 Trauma results in costs for early, follow-up, and possibly long-term care, and also has implications with regard to neural development. Head trauma comes in many forms and has many causes, including accidents and sports injuries. Another type of traumatic injury is purposeful trauma, also known as nonaccidental trauma (NAT) or child abuse. The appearance of the developing skull makes it common for unfused sutures to be mistaken for fractures in young children, and conversely, fractures can be mistaken for normal sutures. Radiolographic evaluation plays a critical role in the diagnosis and characterization of traumatic head injury, and research has suggested an even larger role for it in the future with advanced imaging techniques. 3 ,? 4 ,? 5 A correct understanding of normal developmental anatomy throughout childhood, as well as of the various types of intracranial injuries in pediatric trauma, can allow the appropriate identification of injuries, aiding in their treatment and prognosis.



6.2 Hemorrhage



6.2.1 Appearance of Blood on Computed Tomography


Acutely clotted blood has a density on computed tomography (CT) that is higher than that of brain parenchyma, typically up to 60 to 80 HU. The density is related to the concentrated proteins and heme (which contains iron) in the clot. Unclotted blood will not have this high density, and a hyperacute hemorrhage may not have a uniformly high density, as is the case with the “swirl-sign” of active bleeding into an epidural hematoma (Fig. 6.1). Over time, a hematoma will evolve and decrease in size, and the protein and heme in it are resorbed, resulting in the density of the collected blood decreasing at approximate 1 HU per day. A collection of intermediate density (perhaps 30 HU) is commonly said to be a chronic collection, but may represent an acute collection in a patient with severe anemia.

Fig. 6.1 Epidural hematoma. (a) Axial computed tomographic image shows a lentiform area of increased density along the inner margin of the left squamous temporal bone, with an overlying minimally depressed fracture. (b) Three-dimensional reformatting to display the inner table of the skull shows that the fracture crosses vascular grooves of branches of the middle meningeal artery. (c) Diagram showing the relationship of the disruption in the middle meningeal artery caused by the fracture in an extradural location. (d) Axial computed tomographic image in a 1-year-old male after a head injury, showing a large, lentiform epidural hematoma with a heterogeneous internal appearance that may be indicative of active bleeding, with the areas of low density representing blood products that have not yet clotted. “c” From Atlas of Anatomy, © Thieme 2012, Illustration by Markus Voll.


6.2.2 Dating Hemorrhage on Magnetic Resonance Imaging


The appearance on magnetic resonance imaging (MRI) of evolving blood products relates to both the chemical species of heme in an image and the integrity of the erythrocyte. The evolution of hemoglobin from oxyhemoglobin to deoxyhemoglobin to methemoglobin and then to hemosiderin occurs in a sequential manner but with a highly variable time frame (Table 6-1). Additionally, there is cell lysis, typically during the methemoglobin stage of the evolution. The timing with which the entities in the evolution appear depends upon factors like the presence of continuing bleeding, temperature, pH, and oxygen tension, among others. It is therefore strongly recommended that exact dating of blood products not be attempted with MRI, and even an approximate time window should be suggested with caution in the absence of a full understanding of all of the factors that influence the evolution of blood. Mnemonics exist to assist in remembering the appearance of blood at various stages in T1 W and T2 W images; however, using a mnemonic for this reflects a lack of understanding the process in which blood products evolve, and no attempt should be made to date the blood products if using a mnemonic approach. We will focus on T1 W and T2 W imaging, and later deal with susceptibility-weighted imaging (SWI).















































Table 6.1 Appearance of evolving blood products on magnetic resonance imaging


Blood product


T1-weighted imaging


T2-weighted imaging


Approximate time frame


Hyperacute


Oxyhemoglobin


Isointense


Hyperintense (with a possible hypointense rim)


4–6 h


Acute


Deoxyhemoglobin


Isointense


Hypointense


6 h–3 days


Early subacute


Intracellular methemoglobin


Hyperintense


Hypointense


3–7 days


Late subacute


Extracellular methemoglobin


Hyperintense


Hyperintense


1–6 weeks


Chronic


Hemosiderin


Hypointense


Hypointense


Months to forever


Oxyhemoglobin is present in the first few hours after bleeding. Within a few hours, the oxyhemoglobin degrades to deoxyhemoglobin, which has a hyperintense signal on T1 W MRI. This evolution takes longer in environments with higher pO2 values. After 1 to 5 days, deoxyhemoglobin metabolizes to methemoglobin. Because of proton–electron dipole–dipole interaction (PEDDI), methemoglobin is bright on T1 W imaging. Its hyperintense signal on T1 W imaging is due to PEDDI, but with intact erythrocytes, methemoglobin has hypointense T2 W imaging because of proton relaxation enhancement (PRE). When the erythrocytes lyse, PRE is no longer a factor in the T2 W signal, which then becomes hyperintense. The shortening of the T1 W signal caused by PEDDI is related to the methemoglobin itself and is unaffected by cell lysis. Eventually, the methemoglobin evolves into hemosiderin, which is hypointense on T1 W and T2 W imaging as well as on SWI. Not only is the exact timing of this evolution highly variable, but the evolution of different portions of a hematoma may vary because all of the chemical species in it do not evolve simultaneously.



6.2.3 Subdural Hematoma


A subdural hematoma (SDH) is a collection of blood between the inner and outer dural layers, most commonly related to the traumatic injury of bridging veins. The blood collection that produces an SDH is most commonly located directly subjacent to the site of injury, but with the development of communication of the subdural space, the blood collection in an SDH can redistribute. Subdural hematomas are typically characterized by their location, thickness, and resulting mass effect. These collections are typically of low pressure, filled from venous bleeding, and have a crescentic shape. Because the blood collections in SDH are of low pressure and often do not grow, they are typically followed clinically in the absence of a marked mass effect or neurologic symptoms. However, an SDH can be evacuated neurosurgically if there is concern for its enlargement, a significant mass effect, or a neurologic deficit.


The margins of the falx cerebri and tentorium cerebelli are covered with dural layers, and subdural collections of blood can commonly be seen along these structures (Fig. 6.2). Because the subdural space courses along the surface of these structures, a collection that extends across the falx cerebri or tentorium cerebelli without extension overlying the surface is within the epidural space (Fig. 6.3). Trace subdural blood products overlying the occipital poles and cerebellum can be seen in the early postnatal period in relation to parturition (see Chapter 5), but there will typically be no parenchymal abnormality or resulting mass effect in such cases.

Fig. 6.2 Subdural hematoma. (a) Axial and (b) coronal computed tomographic images in a 7-month-old female following a traumatic injury shows a subdural collection overlying the left frontal lobe (arrows), with extension overlying the falx cerebri (arrowheads). There is local sulcal effacement but no resulting midline shift. (c) Diagram showing the relationship of the hematoma relative to the arachnoid and dura. Note that the “sub” part of “subdural” is relative to the skin surface and not relative to the brain. “c” From Atlas of Anatomy, © Thieme 2012, Illustration by Markus Voll.
Fig. 6.3 Epidural hemorrhage crossing the falx cerebri. Coronal computed tomographic image in a 14-year-old male with history of head trauma shows an extra-axial hematoma (arrowheads). Because this extends between the superior sagittal sinus (arrow) and the calvarium and does not extend along the falx cerebri, it represents an epidural hematoma. Note that the hemorrhage crosses the sagittal suture.

An entity that occurs in young children but rarely in adults is a subdural hematoma with a focal tear in the dural membrane that allows cerebrospinal fluid (CSF) to extend into the subdural space. This is known as a hematohygroma; it can be of lower density on CT than typically expected in an acute collection, and may even be associated with the layering of blood products. An entity with an intermediate-density appearance on CT should not automatically be interpreted as a subacute/chronic hematoma, and the layering of blood products does not automatically indicate an acute-on-chronic hematoma. These concepts are very different from conventional teachings in adult neuroradiology, and awareness of them is exceedingly important (Fig. 6.4). An elderly patient with underlying brain-parenchymal atrophy may have an asymptomatic chronic hematoma. When there is bleeding into this chronic collection, there will be layering of blood products, which are felt to be acute-on-chronic blood products, and in adults this latter belief is usually correct. In children, however, the assumption might be that a volume of low-density material is a chronic hematoma that was previously present but asymptomatic. Given the relative paucity of extra space in the pediatric skull, however, this is not possible; a low-density portion of a collection would be symptomatic. Awareness of this is important because this finding is sometimes described as a mixed-age subdural hematoma suggestive of a hematoma related to NAT. Although the findings in such cases could be related to NAT, they are always likely to be acute. Similarly, patients may have a hematohygroma of intermediate density over one hemisphere and a hematoma overlying the other hemisphere; both of these collections could be acute collections, and should therefore be described as mixed-density subdural collections but not as mixed-age subdural collections.

Fig. 6.4 Layering of blood in subdural hematoma. (a) Axial computed tomographic image in a 4-year-old with a recent traumatic injury shows layering of high-density blood products, with the non-dependent portion of the collection having an intermediate density. This results in approximately 19 mm of right-to-left midline shift, and (b) on an axial computed tomographic image at a lower level there is herniation of the uncus of the temporal lobe (red arrowhead) with mass effect on the brainstem. The patient was normal before experiencing the injury, and the injury represents an acute subdural collection of mixed density (as opposed to an acute-on-chronic collection). There is additionally diminished gray–white-matter differentiation throughout the right cerebral hemisphere, probably related to a mass effect and vascular compromise.

Layering of blood products can also occur within an acute collection in a patient with impaired coagulation as the result of either an intrinsic coagulopathy or pharmacologic therapy. A subdural collection of low density in an anemic patient, such as a child with leukemia, may be an acute, life-threatening emergency. Even the presence of layering blood products may be due to impaired clotting in these patients, who may have thrombocytopenia. Therefore, especially in a patient with anemia or a coagulopathy, such as a leukemia patient, a collection should not be designated as chronic unless a prior study shows that the collection was previously present.

Only gold members can continue reading. Log In or Register to continue

May 28, 2020 | Posted by in NEUROLOGICAL IMAGING | Comments Off on 6 Trauma and Hemorrhage
Premium Wordpress Themes by UFO Themes