Magnetic resonance imaging in myelopathy: a pictorial review

Highlights

• Myelopathies have multiple causes and a broad differential diagnoses.

• Metabolic, vascular and neoplastic diseases can mimic myelopathy and are important to be recognized

• MRI represents a milestone in the diagnostic work-up of myelopathies

• The speed of symptom onset, the length of the spinal cord lesions, the MRI characteristics, the laboratory tests and the evolution are key points for narrowing the differential diagnoses.

Abstract

Myelopathies have multiple causes and broad differential diagnoses, including demyelinating, metabolic, vascular and neoplastic disorders, often with distinctive imaging manifestations.

Compressive myelopathy, especially of degenerative and neoplastic origin, is the most common cause of myelopathy, followed by inflammatory disorders such as multiple sclerosis, acute disseminating encephalomyelitis, neuromyelitis optica, and transverse myelitis of other etiologies.

An accurate and early diagnosis will guide the treatment and will provide information about the prognosis of the patient. The aim of this review is to illustrate the magnetic resonance imaging features of different etiologies of myelopathy.

Introduction

Myelopathy is a collective term referring to any pathologic condition or neurologic deficit related to the spinal cord [1,2]. Myelopathies are a frequent and potentially disabling neurologic emergency. Compressive myelopathy, especially of degenerative and neoplastic origin, is the most common cause of myelopathy, followed by inflammatory disorders such as multiple sclerosis (MS), acute disseminating encephalomyelitis, neuromyelitis optica, and transverse myelitis (TM) of other etiologies. TM is a common presentation of myelopathy as many pathologies present with this pattern, and is divided into idiopathic versus disease-associated forms [1,3,4]. Idiopathic TM is a diagnosis of exclusion, established after ruling out any known etiology, serologic or clinical evidence of connective tissue disease, central nervous system (CNS) manifestations of infections, brain abnormalities suggestive of MS, and history of clinically apparent optic neuritis [3]. Other exclusion criteria for both idiopathic and disease-associated TM are history of spine radiation, signs of vascular malformation and of spinal cord infarction [3,5]. TM is also divided into complete TM, usually with an imaging pattern of longitudinally extensive TM, involving at least three vertebral body segments in length and all or most of the cross-section of the cord, and partial TM, which has less than two segments in length and an eccentric or asymmetric appearance on the cross-section. Distinguishing between the two patterns is helpful in the differential of the underlying etiology and to assess the outcome [3,6]. Furthermore, vascular, infectious, neoplastic and metabolic entities may mimic a primary myelopathy [5,7].

Magnetic resonance imaging (MRI) is the standard imaging technique for evaluating myelopathies and their mimics. Other techniques could also be used for the initial evaluation. Computed tomography (CT) is very useful for revealing bone abnormalities such as fractures, spondylolysis, and for postsurgical evaluation to assess the instrumentation material, the fusion and the potential complications as hematomas and abscesses. CT is the first line technique for trauma patients. CT is also very good in the depiction of ligament ossifications, spinal canal and foraminal stenoses, and spinal cord compression. CT with intravenous contrast and CT myelography could both be useful when MRI is contraindicated or not available. CT myelography is superior for identifying spinal canal or intrathecal pathology when compared to unenhanced CT or to intravenous contrast-enhanced CT. CT spinal angiography and conventional angiography are techniques used in the evaluation of vascular malformations and spinal cord infarcts. The major limitation of all these techniques as compared with MRI is that they could not analyze the intrinsic abnormalities of the spinal cord [1,8].

Important MRI sequences for the evaluation of myelopathy are T1-weighted imaging (T1WI), T2WI, proton density (PD), short-tau inversion recovery (STIR), T2*, diffusion-WI (DWI) and gadolinium-enhanced T1WI. The majority of processes are iso- or hypointense on T1WI, but hyperintense lesions could be revealed especially for hemorrhagic components, fat or melanin. T2WI, PD and STIR usually show hyperintense signal in myelopathies. PD and STIR have higher sensitivity, and particularly in entities such as MS, they could detect significantly more lesions than T2WI. T2* sequences could reveal hemorrhagic components in trauma patients, in underlying tumors and vascular malformations. Myelographic sequences (volumic T2WI) could show cord and radicular compression. DWI could demonstrate diffusion restriction in spinal cord ischemia and abscesses (eg. epidural). As opposed to the brain, fluid attenuating inversion recovery (FLAIR) is not used in spinal cord imaging, being less sensitive due to cerebrospinal fluid pulsation artifact [1,9,10]. Gadolinium-enhanced T1WI could depict variable enhancement patterns (none, diffuse, patchy, peripheral) in inflammatory etiologies, and could give essential information in neoplasias, granulomatous diseases and vascular malformations [[10], [11], [12]]. MRI angiography (MRA), currently fast 3D MRA with contrast enhancement and 4D time-resolved MRA, could be useful in vascular malformations, to demonstrate abnormal vasculature and to guide spinal arteriography [[13], [14], [15]]. Advanced MRI techniques as diffusion tensor imaging, magnetization transfer, myelin water fraction, MRI spectroscopy and functional MRI, are usually research topics [16].

The aim of this review is to illustrate the MRI features of different etiologies and mimics of myelopathy.