Hindawi Publishing Corporation
Case Reports in Medicine
Volume 2012, Article ID 383451, 3 pages
doi:10.1155/2012/383451

Case Report
The Specific Sagittal Magnetic Resonance Imaging of Intradural
Extra-Arachnoid Lumbar Disc Herniation
Tatsuro Sasaji, Kiyoshi Horaguchi, Noboru Yamada, and Kazuo Iwai
Department of Orthopedic Surgery, Fukushima Rosai Hospital, 3-Numajiri, Tsuzura-machi, Uchigo, Iwaki 973-8403, Japan
Correspondence should be addressed to Tatsuro Sasaji, taturosasaji@hotmail.com
Received 3 November 2011; Accepted 28 November 2011
Academic Editor: Jeﬀrey C. Wang
Copyright © 2012 Tatsuro Sasaji et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Intradural extra-arachnoid lumbar disc herniation is a rare disease. Few MRI findings have been reported. We experienced an
intradural extra-arachnoid lumbar disc herniation. We reviewed the preoperative MRI findings. Lumbar spine T2-weighted sagittal
MRI showed that one line of the ventral dura was divided into two by a disc herniation. We speculated that the two lines comprised
the dura and arachnoid and that a disc herniation existed between them. We believe that division of the ventral dural line on T2weighted sagittal images is a characteristic finding of intradural extra-arachnoid lumbar disc herniation. The division of ventral
dural line seemed to be a “Y,” and, thus, we called it the “Y sign.” The “Y sign” may be useful for diagnosing intradural extraarachnoid lumbar disc herniation.

1. Introduction
Intradural extra-arachnoid lumbar disc herniation is a raredisease. Because of its rarity, few preoperative magnetic resonance imaging (MRI) studies have been reported, thus making a preoperative diagnosis diﬃcult. Subdural space leakageof contrast medium by discography is an important criterion
for intradural extra-arachnoid disc herniation [1]. It is
impossible to perform discography for all lumbar disc herniation cases, and no studies have reported specific MRI findings for discography. We experienced an intradural extraarachnoid lumbar disc herniation case; here we report theMRI findings.
The patient was informed that his data would be submitted for publication, and he gave us his consent.

2. Case Report
A 56-year-old male was suﬀering from right thigh pain,
numbness, and gait disturbance for 1 month before presentation.
2.1. Neurological Examination. Neurological examination
showed that his muscle power was normal in lower extremities and his right patellar tendon reflex was absent. Sensory

disturbance was detected in the right thigh. The patient
was diagnosed with right L3 radiculopathy. All laboratory
findings were within normal limits.
2.2. Radiological Findings. Lumbar spine MRI showed a mass
compressing the dura that caudally migrated at the L2-L3
level on T2-weighted sagittal image (Figure 1(a)). The masscontinued to the disc and was assumed to be a lumbar
disc herniation. The ventral dural line was divided into twonear the disc herniation such that the herniation existed
between these lines. The cauda equina was compressed by thedisc herniation on T2-weighted axial images (Figure 1(b)).
Intradural extra-arachnoid disc herniation was diagnosed.
2.3. Operation. The lumbar spine was explored through astraight posterior midline approach. Partial laminectomy atL2-L3 revealed no disc herniation in the epidural space. We
identified a disc herniation in the dura with an ultrasonography (Figure 2). Durotomy revealed fragments covered withthe arachnoid (Figure 3). After removing the fragments, wefound a hole in the ventral aspect of the dura; this hole wasconnected to the disc space. We did not suture the ventral
dural defect to avoid the risk that threads irritate caudaequina.

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L2

(a)

(b)

Figure 1: Preoperative MRI of the lumbar spine: (a) sagittal plane T2-weighted image. (b) Axial plane T2-weighted image. The ventral duralline was divided such that disc herniation existed between the two lines (black arrow) (a). The border of cauda equina and disc herniation
was unclear (b).

2.4. Postoperative Course. The patient’s leg symptom disappeared soon after surgery. One year after surgery, he has
returned to a normal daily life with moderate low back pain.

3. Discussion

L2

L3

Figure 2: Intraoperative ultrasonography. Disc herniation was discovered in the dura (white arrow).

R

CranialFigure 3: Intraoperative photograph. We identified the lumbar discherniation covered with the arachnoid.

Dandy reported intradural lumbar disc herniation for thefirst time; the incidence of intradural lumbar disc herniation
was between 0.04 and 0.33% [2, 3]. Because of rarity,
the diﬀerence in radiological findings between intradural
lumbar disc herniation and typical extradural lumbar discherniation has been unclear. In some reports, the diagnosis
was confirmed intraoperatively [4–6]. The preoperative
diagnosis of intradural lumbar disc herniation has beendiﬃcult. We thought that the characteristic radiologicalfindings of intradural lumbar disc herniation were necessary.
Choi et al. reported useful MRI findings such as the“hawk-beak sign” and abrupt loss of posterior longitudinal
ligament continuity [7]. The “hawk-beak sign” was a sharp
compressing lesion with a beak-like appearance to the duralsac on T2-weighted axial images. However, these findings
may not be specific to intradural lumbar disc herniation
and were not observed in our case. According to Whittakerand D’Andrea et al., MRI with gadolinium was useful for
diagnosis [8, 9]; however, contrast-enhanced MRI may be
impossible in all lumbar disc herniation cases. Intradural
extra-arachnoid disc herniation occurs between the duraand arachnoid (Figure 4). In the case of intradural extraarachnoid disc herniation, the arachnoid was peeled fromthe dura by the disc herniation. One line of the dura andarachnoid was divided into two lines of the dura and thearachnoid. The branch of the ventral dural line appeared as“Y.” This branch may have been a characteristic appearance

Case Reports in Medicine

Vertebral
bodyDisc

Vertebral
body

Figure 4: Schema for intradural extra-arachnoid lumbar disc herniation. An intradural extra-arachnoid lumbar disc herniation
existed between the dura and arachnoid. The division of dura andarachnoid appeared as “Y” (shaded area: disc herniation; solid line:dura; dotted line: arachnoid; black arrow: “Y sign”).

of intradural extra-arachnoid lumbar disc herniation, and,thus, we called it the “Y sign.” To our knowledge, such findings have not been reported previously.

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474–477, 1942.
[3] O. Kataoka, Y. Nishibayashi, and T. Sho, “Intradural lumbar
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[4] S. Kuba, T. Uchida, E. Aso, and T. Tomonaga, “A case report of intradural lumbar disc herniation,” Orthopedics andTraumatology, vol. 56, pp. 49–52, 2007 (Japanese).
[5] T. Hamasaki, T. Noda, S. Yamamoto, J. Nakajo, and T. Sugioka,“Intradural lumbar disc herniation. Report of three cases,” TheCentral Japan Journal of Orthopaedic Surgery & Traumatology,
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[8] C. K. Whittaker and M. Bernhardt, “Magnetic resonance imaging shows gadolinium enhancement of intradural herniateddisc,” Spine, vol. 19, no. 13, pp. 1505–1507, 1994.
[9] G. D’Andrea, G. Trillò, R. Roperto, P. Celli, E. R. Orlando,and L. Ferrante, “Intradural lumbar disc herniations: the roleof MRI in preoperative diagnosis and review of the literature,”
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