Category: Neuroradiology, Region: Head-Meninges, Plane: Axial
Case Report Our patient, a 72 year old female with a past history of a right frontoparietal stroke and residual left hemiparesis, presented to the emergency room with a one day history of headache and confusion. One month previously she had been diagnosed with a deep venous thrombosis in her leg and had been started on lovenox and Coumadin. There was no reported history of antecedent trauma. Review of systems, other than the residual deficits from her previous infarct, was noncontributory. A noncontrast head CT (Computed tomography) was subsequently performed and demonstrated an area of extra-axial hyperdensity marginating the clivus and extending from the most inferiorly visualized aspect of the anterior foramen magnum cephalad towards the left and right cerebellopontine angle cisterns. (figs 1, 2). A subdural hemorrhage was suspected. Less likely considerations included an extra –axial hypercellular mass such as a meningioma, lymphoma, or plasmacytoma. A CT angiogram of the head and neck was performed next to exclude any regional vascular anomalies such as an occult arteriovenous malformation or dissection as well as to assess for any abnormal regional enhancement. There was no evidence of an underlying enhancing mass or regional aberrant vessels (figs 2,3). Elevation and dorsal displacement of the distal V4 verterbral artery segements and the basilar artery was observed. Anticoagulation was reversed in the emergency room with fresh frozen plasma and vitamin K was begun; the patient was subsequently admitted for supportive care and observation. An MRI (Magnetic resonance imaging ) of the brain and cervical spine, ordered to ensure a bland nature of the hemorrhage and to completely exclude any underlying mass, demonstrated the hematoma to have predominantly low signal on T2 FSE (Fast spin echo) images and high signal on T1, consistent with intracellular methemoglobin. There was dissection from the superior aspect of the clivus distally through the anterior foramen magnum into the ventral spinal canal. The hematoma was noted to overlay an intact, otherwise unremarkable tectorial membrane and to extend distal to the membrane attachment at the dorsal mid C2 vertebral body, consistent with a subdural location. (figs 5,6) As a final step in the workup, a four vessel cerebral angiogram, not shown, was done to exclude any small contributory distal vertebral aneurysms and proved negative in this regard. After an uneventful 10 day hospital course during which temporal evolution and progressive resolution of the hemorrhage was observed on a follow up CT exam, the patient was discharged back to a skilled nursing care facility. Deep venous thrombosis prophylaxis was reinitiated with subcutaneous heparin and a return appointment as an outpatient with the neurosurgery clinic was scheduled. Discussion Retroclival hematoma is an uncommon finding, typically occurring in the epidural space in pediatric patients following significant blunt trauma. There are usually coexisting injuries to the skull base or craniocervical ligaments, most commonly the tectorial membrane [2,7]. Clival hematomas have been recognized as an unusual complication of severe head and neck injury and are often accompanied by atlantoaxial dislocation . The hemorrhage may compress the brainstem resulting in altered levels of consciousness, paresis and paralysis. As with subdural hematomas at this level, cranial nerve palsies may also occur. Most commonly the sixth nerve is affected resulting in lateral rectus palsy due to its relatively longer course of exposure as it ascends from the pontomedullary junction to the petrous apex and Dorello’s canal . Children are more predisposed for epidural hemorrhage at this level due to their higher fulcrum of cranial cervical motion and relative ligamentous laxity. The abrupt acceleration/deceleration injury that ensues in high energy blunt trauma strips the tectorial membrane from the occipital bone at the foramen magnum and the posterior aspect of the C1 anterior arch . Concomitant shearing of the vessels of the basilar venous plexus and dorsal meningeal branch of the meningohypophyseal trunk results into either mixed, venous or arterial bleeding within the epidural space . Stretching injury to the tectorial membrane was seen in 70% of patients in one surgical series . As with subdural hemorrhage at this level, the typical CT finding is focal hyperdensity posterior to the clivus with variable degrees of mass effect upon the adjacent brainstem. MRI is of utility in defining the extent of the hemorrhage and in evaluating for concomitant soft tissue injury as manifest by loss of ligamentous continuity or as increased internal T2 signal in the case of an incomplete tear . As opposed to epidural hemorrhage, bleeding in the subdural space at this level is not constrained by ligamentous attachments and is free to diffuse into the spinal subdural space inferior to the C1-2 level as well cranially into the ventral and retrocerebellar aspects of the posterior fossa. [2,6] Additionally, the tectorial membrane is typically intact and firmly attached both to the clivus and at its inferior attachment at the posterior mid axis body. The hemorrhage is thought to be due to disruption of petrosal and bridging cortical veins at the foramen magnum . Retroclival subdural hematomas are overall less common than epidural hemorrhage at this location and occur more often in the adult population [1,2,7]. Overall they represent only 0.3% of acute subdurals.  Though trauma may be an inciting factor, other etiologies reported have included hemophilia or iatrogenic anticoagulation, pituitary apoplexy, ruptured AVM, and decompressive craniectomy. [1,3,4,9,10]. The clinical presentation may mimic that of a subarachnoid hemorrhage with abrupt onset of a thunderclap headache. [5,11] Cranial nerve palsies may ensue secondary to locoregional mass effect, typically the 6th nerve being most commonly affected. The hemorrhage, as previously stated, can diffuse into the subdural space of the spine and posterior fossa. MRI will best show typically high T1 methemoglobin extending distal to the mid-axis body, overlying the intact, uninjured tectorial membrane at the craniocervical junction. Additionally the presence of hemorrhage extending more laterally and posteriorly at the foramen magnum supports a subdural location [2,5]. Other differential considerations include extra–axial hypercellular masses such as a meningioma, lymphoma, or plasmacytoma. Meningiomas are typically slightly hyperdense (60%) to isodense to normal brain and 20-30% demonstrate some calcification. On T1 MRI they can be isointense: (~60-90%) to somewhat hypointense: (10-40%) compared to grey matter, demonstrate intense and homogeneous enhancement, and on T2 MRI imaging they can be isointense (~50%) to hyperintense (35-40%) . CNS lymphoma is typically hyperattenuating (70%) on CT, hypointense to white matter on T1 MRI, and iso- to hypointense on T2 MRI. Hyperintensity is more common in lymphoma with necrosis. Typical high grade CNS lymphoma shows strong homogeneous enhancement while low grade tumors have absent to moderate enhancement . Plasmacytomas usually arise from the bone and can be exophytic from the clivus mimicking an intracranial mass or hematoma. On CT they appear as expansile lytic or hyperintense lesions with thinned out cortex. On MRI they usually demonstrate hypo- to isointense T1 enhancement and iso- to hyperintense T2 enhancement. They typically demonstrate variable contrast enhancement . Given the potential association with underlying vascular malformations, it was felt prudent in our case, as had been done in other reported instances, to proceed with catheter angiography to completely exclude an underlying anomaly. In other published cases, however, CT angiography and MR imaging alone have been felt to suffice [5,10,11]. In the absence of significant comorbidities, the overall prognosis is good. Without neurological deficits, management is conservative and expectant with most hematomas clearing by two weeks [1,2,5]. Management is based on the extent of any neurological and soft tissue co-injuries and only in their absence is care expectant and conservative. Treatment options for spinal subdural hematomas vary from urgent operative intervention to watchful management. Though an uncommon entity, retroclival hematomas are an important diagnostic finding to make due to their potential for significant neural compression as well as their association with underlying osseous and ligamentous injury especially in the pediatric population. Epidural hemorrhage, as seen in this group, will typically be constrained by an overlying attenuated tectorial membrane, partially stripped from the clivus and subjacent atlanto-axial junction in comparison to subdural bleeding, which can diffuse freely into the posterior fossa and spinal subdural spaces and may be seen posteriorly and laterally at the level of the foramen magnum or extending below the mid axis body. Teaching Point Retroclival hematoma is a relatively uncommon entity most often occurring in the pediatric population in the epidural space in conjunction with blunt trauma and injury to the skull base or tectorial membrane, and subdural bleeding in this location is even less common, representing only 1% of all intracranial subdural hemorrhages and occurring more often in adult patients. Besides traumatic injury, other inciting factors in the literature have included arteriovenous malformations, suboccipital decompression, pituitary apoplexy, hemophilia, and anti-coagulation. References 1. Guillaume D, Menezes A (2006) Retroclival hematoma in the pediatric population: Report of two cases and review of the literature. J. Neurosurg: Pediatrics 105:321-325 2. Koshy J, Scheurkogel M, Clough L, et al (2014) Neuroimaging findings of retroclival hemorrhage in children: a diagnostic conundrum. Childs Nerv Syst 30:835-839 3. 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