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 Table of Contents  
Year : 2018  |  Volume : 1  |  Issue : 1  |  Page : 61-64

Dorsally migrated epidural disc herniation with intradural extension: A rare clinical entity

1 Department of Neurological Surgery, The Ohio State University, Columbus, Ohio 43202, USA
2 Department of Spine Surgery, Ganga Medical Center and Hospitals Private Limited, Coimbatore, Tamil Nadu, India
3 Department of Radiodiagnosis Surgery, Ganga Medical Center and Hospitals Private Limited, Coimbatore, Tamil Nadu, India

Date of Web Publication17-Jan-2018

Correspondence Address:
Dr. Ajoy Prasad Shetty
Department of Spine Surgery, Ganga Medical Center and Hospitals Private Limited, 313, Mettupalayam Road, Sai Baba Koil, Coimbatore - 641 043, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/isj.isj_12_17

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Migration of disc fragment into the dorsal epidural space is a rare phenomenon. It happens when a sequestrated disc fragment transgresses the anatomical barriers to reach dorsal to the dural sheath. We describe a rare situation where a dorsally migrated, sequestrated disc fragment also had a partial intradural extension. The case is highlighted for the extreme rarity of such presentation, role of magnetic resonance imaging scan on the preoperative diagnosis and crucial surgical principles.

Keywords: Dorsally epidural space migration, partial intradural extension, sequestrated disc herniation

How to cite this article:
Viswanathan VK, Shetty AP, Kanna RM, Mahesh A, Shanmuganathan R. Dorsally migrated epidural disc herniation with intradural extension: A rare clinical entity. Indian Spine J 2018;1:61-4

How to cite this URL:
Viswanathan VK, Shetty AP, Kanna RM, Mahesh A, Shanmuganathan R. Dorsally migrated epidural disc herniation with intradural extension: A rare clinical entity. Indian Spine J [serial online] 2018 [cited 2020 Aug 7];1:61-4. Available from: http://www.isjonline.com/text.asp?2018/1/1/61/223440

  Introduction Top

Herniated lumbar disc fragments commonly migrate in rostral, caudal, and lateral directions.[1] Rarely, the sequestrated disc fragment is known to migrate dorsal to the dural sac.[2],[3] In such situations, the prolapsed disc occupies the epidural space underneath the lamina.[2],[3] Chronically presenting disc herniations have also been reported to violate the duramater and exist intradurally. We hereby describe a case, where a dorsally located disc fragment also presented with a partial intradural extension. Such a combination of presentation is of extreme rarity; and can complicate the clinical, radiological presentation, as well as management.

  Case Report Top

A 45-year-old female presented with low back pain and severe bilateral L5 radicular pain (predominantly right-sided) over the past two weeks; recalcitrant to oral analgesics. The patient had developed weakness of bilateral L4, 5 myotomes with urinary hesitancy of 52-h duration. On examination, the motor deficit was present at L4, 5 myotomes (power of 1/5 in bilateral L5 and 3/5 in bilateral L4 myotomes), and the ankle reflexes were absent bilaterally and hypoesthesia at L4, 5 dermatomes on both the lower limbs. The anal tone was reduced with decreased perianal sensation.

Plain radiographs showed loss of lordosis with degenerative spondylotic changes. Magnetic resonance imaging (MRI) revealed a large extradural mass lesion at L4–L5 disc level, which was predominantly hypointense on T1 and of isointense on T2-weighted imaging (WI) [Figure 1]a, [Figure 1]b and [Figure 2]a, [Figure 2]b, located dorsal to the dural sac and significantly compressing the cauda equina. On mid sagittal T1WI, the epidural fat was completely obliterated. Gadolinium enhanced films revealed a ring shaped enhancement, which was indicative of a probable disc fragment. Sagittal section revealed the dural tail like extension inferiorly, which was more clearly noticed on contrast enhancement [Figure 3]. With this peculiar morphology, the differential diagnoses which were considered preoperatively included epidural lesions including sequestrated dorsal disc fragment, tumor, dermoid cyst, hematoma, or epidural abscess. Laboratory values, including erythrocyte sedimentation rate and C-reactive proteins, were within normal limits.
Figure 1: Preoperative T1-weighted magnetic resonance imaging scan (a) sagittal section images at the mid-sagittal plane showing epidural mass compressing the cauda equina at L4–L5 level (b) corresponding axial image at L4–L5 level showing large epidural mass lesion significantly compressing the cauda equina

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Figure 2: Preoperative T2-weighted imaging magnetic resonance imaging scan (a) sagittal section images at the mid-sagittal plane showing epidural mass compressing the cauda equina at L4–L5 level. Beak-like flange is visible at this section, which may suggest an intradural component (b) corresponding axial image at L4–L5 level showing large epidural mass lesion significantly compressing the cauda equina

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Figure 3: Preoperative gadolinium-enhanced magnetic resonance imaging scan. Sagittal section at mid-sagittal plane showing an epidural mass with dural tail and peripheral enhancement

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The surgical exploration was performed under the guidance of microscope, and conventional L4 laminectomy was done. Intraoperatively, there was large disc fragment which could be identified just underneath the lamina. As the disc fragment was gradually dissected, a small rent was identified in the posterior dural sac, through which a large part of the disc fragment extended intradurally [Figure 4]. All fragments were gradually mobilized and meticulously excised using pituitary Rongeurs and Adson hook. The dural repair was done with continuous sutures using 5-0 Prolene. The histopathological evaluation of the mass confirmed the diagnosis of herniated disc fragment. The patient had significant neurological recovery postoperatively, and at one year follow up, the patient has completely recovered.
Figure 4: Intraoperative images: Intraoperative picture showing (a) dorsally migrated disc fragment with adjacent dural rent (b) intradurally migrated portion of the sequestrated disc gradually delivered out

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  Discussion Top

Disc herniation with posterior epidural migration is a rare entity with a reported incidence of 0.27%.[4] It was first reported by Lombardi et al. in 1973, and such an occurrence has since then been described predominantly at L3–L4 and L4–L5 level.[5] The anatomical barriers restraining such migrations include dura, posterior longitudinal ligament (PLL), septum posticum (tough midline structure attaching periosteum of vertebral bodies to PLL), lateral peridural membrane of Fick (extending deeper to PLL), ligament of Hoffmann (between PLL and dura), and other contents of the epidural space (including nerve roots, fat, and Batson's epidural venous plexus).[6] Since the disc fragments follow the path of least resistance, these barriers effectively contain the herniated contents to the ventral compartment of the spinal canal in most instances. However, rarely, the herniated disc may go beyond the usual boundaries and may present in the dorsal epidural space.

As the disc fragments migrate dorsally, they transgress most of the anatomical barriers and vital neural elements, resulting in more severe clinical presentation and higher chance of neurological deficit.[2] During the process of posterior migration, the sequestrated disc fragment gets walled by vascular epidural fat, which induces an inflammatory cascade and leads to ensuant development of granulation tissue surrounding it. This reactive tissue leads to the development of circumferential and peripheral rim enhancements in such dorsally migrated discs, which has classically been described in epidural infections or certain metastatic lesions.[3]

Intradural encroachment by a herniated disc fragment was initially described by Dandy in 1942 and is reported in 0.33% of disc herniations.[7],[8] Most of the reports in the literature describe an anterior dural violation by a herniated disc fragment. To the best of our knowledge, this is the first reported instance of a dorsally migrated disc fragment infringing on the subdural compartment and presenting with a partial intradural component. Various pathomechanisms have been described to explain the transdural migration of herniated nucleus pulposus. Floeth and Herdmann [9] reported that in the presence of dense adhesions between the dural and peridural tissues (due to congenital bands, trauma, postsurgery, postinflammation, and adhesions secondary to large discs or osteophytes), herniated disc fragments work like a “finger-tip” and the relative movements between the lumbar spine and partly fixated dural sac lead to chronic inflammation, erosion, and thinning of the dural sac. Such weak zones of the dural form the entry points for the herniated fragments. Choi et al.[10] reported three major predisposing factors for such intradural disc migrations: (a) Congenitally narrowed spinal canal with compromised epidural space; (b) occurrence of adhesions between annulus fibrosus, PLL, and dura mater; and (c) congenital or iatrogenic fineness of the dural sheath.

In our patient, a large, chronic dorsally migrated, sequestrated epidural disc fragment caused gradual dural thinning and inflammation. Since there was significant primary canal stenosis, the epidural space was significantly compromised; and hence, the dural violation would have occurred secondary to chronic erosion of dura mater. Intraoperatively, adhesions were evident between the disc material and dural elements.

Based on the current literature, the imaging findings on T1 and T2 sequences are variable and nonspecific.[11],[12] MRI with gadolinium administration is the investigation of choice in these circumstances.[7] Sequestrated disc fragments show hypointense signal on T1WI and hyper- (in 80%) or isointense signal on T2WI. Peripheral rim contrast enhancement occurs on gadolinium administration. Tumors enhance uniformly with contrast. Dermoid tumors present with hyperintense lesion on T1WI. Abscesses present with hypointense T1 and hyperintense T2 signals with peripheral contrast enhancement, nevertheless are invariably accompanied by typical changes in the disc space. Hematomas have iso- or hyperintensity on T1-weighted images with no enhancement. One of the most important characteristics which distinguishes a dorsally migrated disc fragment from the other differential diagnoses is that the abnormality (in the case of a disc herniation) not only occupies the dorsal epidural space but also contacts the parent disc in the ventral epidural space, asymmetrically crosses the lateral epidural space to reach the posterior epidural location.[12]

Zarrabian et al.[13] reported these two specific findings on axial MRI as clinching factors to aid in the diagnosis of dorsal lumbar disc herniation in a dorsal or dorsolateral epidural soft-tissue mass: (a) Asymmetric epidural space lateral to thecal sac and (b) lesion spanning from ventral/ventrolateral to dorsal/dorsolateral, instead of being pure dorsal. This spanning lesion either represents disc material or granulation tissue along the path of migrated disc. Chen et al.[8] described this phenomenon as the contributing mechanism to enhanced uptake over a tract-like pattern in dorsally migrated disc herniations.

In 2010, Akhaddar et al.[14] performed a systematic review on posteriorly migrated disc herniations. A total of 46 patients were included in this review (1965–2010). Since then, 12 more patients have been reported in the literature. Most patients were male (78.8%), and the presenting symptoms in decreasing order of frequency included back pain (91.5%), radicular leg pain (74.5%), leg weakness (38.3%), sphincter disturbances (31.2%), numbness (29.2%), and neurogenic claudication (2.1%). Rahimkizadeh et al.[15] reviewed the literature on dorsal disc herniations and observed that 50% of these patients developed cauda equina syndrome. About 71.8% of patients in the systematic review by Akhaddar et al.[14] achieved total neurological recovery following surgery.

Typical findings in intradural disc herniations are abrupt interruption of PLL and continuation of the intradural tissue with the intervertebral disc. A sudden discontinuity in the PLL needs to be looked on with suspicion, as it can represent the only indication for a possible intradural communication of the disc material.[10] Certain specific radiological signs have been described to diagnose ventrally migrated intradural disc fragments, following anterior dural surface violation. Choi et al.[10] described the “hawk-beak” sign on axial MRI scan, which represented a beak-like appearance of the dura imparted by the sharp, compressing lesion. Sasaji et al.[16],[17] described a unique situation of intradural, extraarachnoid disc prolapses, which occurs when the disc fragment gradually peels off the arachnoid mater from the dural layer and occupies the subdural space. They proposed a “Y-sign” on sagittal MRI scan images, which indicates the separated dural sheath and arachnoid. At times, the disc materials can be entirely intradural. Most of the reports in the literature thus describe an intradural extension of disc fragment through a rent in the ventral dura.[16],[17] In our case, the disc was predominantly dorsal to the dura and extended through a defect in the posterior dural surface. In such situations, the preoperative diagnosis of a subdural extension may be even more difficult. In our patient, we could identify a positive “dural tail” sign [18] on contrast-enhanced sagittal MRI, which has been classically described in meningiomas. However, this sign is relatively nonspecific and has been described in other lesions such as neuromas, chloromas, metastases, lymphoma, gliomas, large disc sequestrations, and granulomatous disease. It represents a postcontrast linear thickening of the meninges that resembles a tail extending from the mass lesion. In our patient, it was possibly the only indication for considering a dural extension of the predominantly extradural mass.

In such atypical conditions, it may be safer to consider laminectomy over other minimally invasive approaches (like interlaminar or endoscopic), as it facilitates complete exploration, allows safer resection of adhesions, and obviates complications including dural tear or incomplete disc excision.[3],[4] Akhaddar et al.[14] described the procedure of discectomy in posteriorly migrated disc prolapses and observed that these herniations usually have minimal adhesions to dural tissue, and therefore, can be excised completely. However, when there is an intradural extension, the complete excision of the disc remains a challenge. One should be aware of the existence of dense adhesions around the dural tissues in such scenarios, and careful dissection is of utmost importance. Whenever an intradural disc fragment is suspected preoperatively, careful examination of the dura for rents and residual disc elements is mandatory. Incomplete removal of disc materials can result in persistent or worsening of symptoms.[19],[20] The neurological outcome following dorsally migrated disc herniations is generally much better than ventral disc herniations. This is possibly explained by the greater availability of epidural space dorsal to the thecal sac, in comparison with the ventral epidural space.[14]

We, thus, wish to highlight the extreme rarity of such a scenario involving a partial intradural extension of dorsally migrated disc sequestrum. The pitfalls in routine imaging modalities, need for additional contrast enhancement in diagnosis, clinical and diagnostic dilemma involved in such situations, need for careful examination of dural elements for residual disc fragments intraoperatively, and implications of incomplete removal of disc material have been discussed. The presence of a dural tail on sagittal, contrast-enhanced MRI can be suggestive of such a presentation.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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