Discussion:
Thoracic spinal cord herniation is a rarely reported diagnosis in the literature. The rarity may partly be due to the difficulty in arriving at the diagnosis due to inconsistent clinical findings[5]. The first case was reported by wortzman G et al when high resolution MRI was not available for diagnosis[6]. The study group identified a progressive Brown-Sequard-like syndrome which was not explained by the usual etiology[6]. The majority of the spontaneous thoracic cord herniations reported in the literature are in the form of single case reports and we found less than 220 cases in the entire literature to date[1]. Most of the cases of herniations are localised between the thoracic third and seventh segments in the middle-aged individuals[7]. The herniation of the spinal cord through the dura usually occurs through the anterior or anterolateral part of the dural sheath[1]. The dorsal herniation is very rare[4]. There are few postulated theories for the herniation of the spinal cord which include congenital dural deficiency with a preexisting anterior meningocele, traumatic etiology, duplication of anterior dura, and microscopic erosion of anterior dura during repeated flexion and extension but none of these etiologies are proven in literature[1, 2]. So, this condition is often referred to as an idiopathic condition[2].
The cases of spinal cord herniation show a wide spectrum of symptoms. The usual presenting symptom is progressive Brown-Sequard type of syndrome with contralateral altered pain and temperature with ipsilateral hemiparesis[3]. The neurological deficits may or may not follow the dermatomal/myotomal distribution. The adhesion of the spinal cord to the surrounding structures and resultant vascular compromise are thought to cause neurological deficits[4]. Due to these non-standard symptoms, many cases of spinal cord herniations were misdiagnosed as medical causes of paraplegia like multiple sclerosis, demyelinating neuropathy, and sub-acute combined degeneration of spinal cord[8]. With the wide-spread use of MRI for the diagnosis of spinal conditions, many cases of spinal cord herniations are being reported in the recent past. The MRI sagittal view would show focal anterior displacement of the spinal cord and the axial view shows a lateral defect in the dura and herniation of the spinal cord[9]. Care must be taken not to miss the arachnoid cysts if they are present with spinal cord herniations[9]. The nerve roots are visible in the periphery of the arachnoid cysts whereas the nerve roots are visible in the dorsal subarachnoid region in the case of spinal cord herniations without arachnoid cysts[1, 9].
The usual treatment in patients presenting with neurological deficits and with a diagnosis of spinal cord herniation is surgical repair of the herniation[10]. The repair is focused on reducing the cord contents into the dura and closing the defect. Reducing the cord into the dura has been shown to improve neurological symptoms[11]. There are few cases where the symptoms have deteriorated even after surgical intervention. The cause could be late retethering or the development of hematoma causing compression. In our case, although the neurological deficits improved after surgery, there was a sudden deterioration of the neurology on the third day. This is usually due to hematoma causing mechanical compression or occlusion of venous drainage. In our case, the etiology was hematoma and removal of hematoma satisfactorily treated the symptoms. Ammar et al reported spontaneous retethering in patients with spinal cord herniation after treatment[12]. The patient should be kept in constant follow-up and the retethering symptoms should be explained in detail at discharge.
The evidence available in the literature for treating spontaneous spinal cord herniations is limited to case reports and few case series. As there are reports stating spontaneous reduction of the hernia and deterioration of symptoms after surgery, strong guidelines for the management of spinal cord herniations are lacking[1]. With the extensive use of MRI, the number of cases diagnosed as spinal cord herniation is increasing and strong evidence-based guidelines for which patients to be treated surgically are the need of the hour.