CCRN Neurological, Musculoskeletal and Behavioral Questions

The halo or ring sign is a classical bedside assessment used to detect cerebrospinal fluid leakage in patients with suspected basilar skull fractures. When serosanguineous nasal or otic discharge is placed onto filter paper or sterile gauze, the components separate based on physical density and viscosity; the heavier cellular elements of blood remain in the center, while the clearer, less viscous cerebrospinal fluid diffuses peripherally, producing a clear ring developing around a central blood stain. Uniform pink diffusion across the entire gauze surface reflects homogeneous mixing of serum and erythrocytes without separation, which is characteristic of simple blood dilution or mucus rather than cerebrospinal fluid. A central clear droplet surrounded by thick clotted blood is physiologically backwards, as dense erythrocytes do not migrate faster than aqueous cerebrospinal fluid. Formation of a yellowish ring around clear serum is typical of pure exudative drainage or plasma transudate lacking cellular blood components. While beta-2 transferrin testing is the definitive laboratory standard, identifying the classic halo sign immediately alerts the clinician to cribriform plate or dural disruption.

Subdural hematomas develop in the space between the dura mater and arachnoid mater. The classic pathophysiology involves mechanical shearing or tearing of the bridging veins traversing the subdural space, which drain venous blood from the cerebral cortex into the superior sagittal sinus. In elderly individuals, cerebral atrophy stretches these delicate bridging veins, making them extraordinarily susceptible to rupture even after minor head trauma, while anticoagulants like warfarin accelerate hematoma expansion. Middle meningeal artery within the epidural space causes an epidural hematoma, which typically appears as a biconvex, lenticular hyperdensity that does not cross suture lines. Anterior communicating artery within the subarachnoid cisterns is the primary site for saccular aneurysm rupture leading to diffuse subarachnoid hemorrhage rather than a focal extra-axial subdural collection. Basilar venous plexus along the clivus can be injured in high-energy skull base fractures causing petroclival or posterior fossa bleeding, not supratentorial crescentic subdural hematomas. Bridging vein rupture produces insidious low-pressure venous bleeding that crosses cranial sutures while respecting dural reflections.

Kernig sign is an established physical assessment maneuver used to identify irritation of the meninges and spinal nerve roots, commonly seen in bacterial meningitis or subarachnoid hemorrhage. It is elicited with the patient positioned supine; the examiner flexes the hip and knee to 90 degrees and then attempts passive extension of the knee. The sign is positive when passive extension produces resistance and severe hamstring pain caused by stretching inflamed meninges. Involuntary flexion of hips when neck is flexed describes Brudzinski sign, which is an alternative physical manifestation of meningeal inflammation rather than Kernig sign. Pupillary dilation and bradycardia are signs of brainstem compression or impending herniation; they are not elicited by neck flexion and are not a test of meningeal irritation. Dorsiflexion of great toe upon stroking lateral foot describes a positive Babinski response, an indicator of upper motor neuron pathway dysfunction rather than meningeal irritation. Recognizing a positive Kernig sign assists the critical care nurse in prioritizing emergent lumbar puncture, diagnostic imaging, and prompt administration of empiric intravenous antibiotics and corticosteroids.

The classic presentation of an epidural hematoma is an initial loss of consciousness caused by the impact, followed by a transient lucid interval during which the patient appears neurologically intact, followed by rapid secondary neurological deterioration. This pathology typically results from fracture of the temporal bone lacerating the middle meningeal artery. Expanding arterial bleeding rapidly strips the dura from the inner skull table, elevating intracranial pressure and precipitating uncal herniation, evidenced by ipsilateral oculomotor nerve compression causing a dilated, sluggish pupil. An acute subdural hematoma results from tearing of cortical bridging veins; it presents with immediate, progressive neurological decline without a pronounced classical lucid interval. Diffuse axonal injury involves widespread shear injury to axons and presents with immediate, prolonged coma from the moment of impact. Post-concussive syndrome presents with headache, dizziness, and cognitive difficulties, never with acute obtundation, pupillary asymmetry, or signs of impending brain herniation.

Diffuse axonal injury results from severe rotational acceleration-deceleration forces that generate violent shearing and tensile stresses across brain tissue layers of differing densities. These forces cause microscopic disruption of the neuronal cytoskeleton and widespread axonal tearing, characteristically located at the grey-white matter junction, corpus callosum, and brainstem. Clinically, patients present in immediate and profound coma that is markedly disproportionate to the subtle abnormalities seen on initial computed tomography imaging, which often reveals only faint punctate microhemorrhages. Direct mechanical impact causing focal parenchymal contusions results in localized coup and contrecoup cerebral injuries, which appear as prominent localized hyperdense areas with surrounding edema on initial imaging. Middle meningeal arterial laceration causes an acute epidural hematoma, presenting with a classical biconvex lenticular collection that rapidly expands between the skull and dura. Bridging cortical venous rupture causes an acute subdural hematoma, which forms a crescent-shaped hyperdensity along the cerebral hemisphere. Neither focal contusions nor extra-axial hematomas explain widespread microscopic axonal disruption with an initially unremarkable scan.

Anterior cord syndrome typically results from hyperflexion injuries or occlusion of the anterior spinal artery, leading to ischemia or infarction of the anterior two-thirds of the spinal cord. This injury damages the corticospinal tracts, resulting in bilateral loss of motor function below the level of the lesion, and damages the spinothalamic tracts, causing bilateral loss of pain and temperature sensation. Because the dorsal (posterior) columns receive blood supply from the paired posterior spinal arteries, vibration, proprioception, and deep touch sensation are preserved. In contrast, central cord syndrome predominantly affects the central gray matter and medial corticospinal tracts, causing motor weakness and sensory impairment that is significantly greater in the upper extremities than in the lower extremities. Brown-Sequard syndrome is characterized by a spinal cord hemisection producing ipsilateral motor paralysis and loss of proprioception, alongside contralateral loss of pain and temperature sensation. Posterior cord syndrome is a rare condition marked by the isolated loss of proprioception, vibration, and fine touch, while voluntary motor function, pain, and temperature sensation remain completely intact.

The Glasgow Coma Scale (GCS) motor response evaluates central nervous system integrity and serves as a sensitive indicator of neurological deterioration. Decorticate posturing (abnormal flexion), characterized by adduction and flexion of the arms with wrist flexion against the chest and leg extension, indicates cerebral hemispheric dysfunction or midbrain sparing, scoring a 3 on the motor subscale. Decerebrate posturing (abnormal extension), characterized by rigid extension, adduction, and internal rotation/hyperpronation of the upper extremities with plantar flexion, indicates deeper brainstem damage at the pontine or midbrain level, scoring a 2. Therefore, progression from decorticate to decerebrate posturing reflects worsening rostral-to-caudal neurological deterioration with a decrease in the motor score from 3 to 2. A decrease from 4 to 3 would represent a change from withdrawal from pain to abnormal (decorticate) flexion, which is not the change described. A motor score decreases from 2 to 1 indicates progression from extension to flaccidity, rather than abnormal flexion to extension. A motor score increases from 2 to 3 describes neurological improvement from extension to flexion, contradicting the patient's acute neurological herniation pattern.