Key-words:
Discal cyst - discectomy - endoscopy - percutaneous endoscopic interlaminar lumbar
discectomy - percutaneous endoscopic lumbar discectomy - percutaneous endoscopic transforaminal
lumbar discectomy
Introduction
Discal cysts are a rare pathology of low back pain and radiculopathy, most commonly
affecting the young Asian population.[[1]],[[2]],[[3]],[[4]] It is defined as an intraspinal extradural cyst with distinct communication with
the corresponding intervertebral disc.[[1]],[[3]],[[5]] It is imperative to recognize intraspinal discal cysts as a source of back pain
and radiculopathy, especially in young adults with no other degenerative features.[[6]] This report on two patients managed at our institute, describes endoscopic view
of the discal cyst with a mention of all the layers including the capsule, the hard
and melting part of the cyst as well as rent within the underlying disc, thus reinforcing
the origin of such rare entity. Percutaneous endoscopic lumbar discectomy (PELD),
a recently described technique for discal cysts is the treatment of choice due to
the explicit intraoperative vision of the pathology as well as early recovery with
minimal morbidity.
Case Reports
Case 1
A 31-year-old man complained of low back pain and left leg pain for 3 months. On examination,
straight leg raising test (SLRT) was positive on the left side and left great toe
had planter flexion Grade 4 weakness. Magnetic resonance imaging (MRI) [[Figure 1]] showed a small left-sided L5-S1 disc herniation and a cystic mass in the left lateral
aspect of the ventral extradural space from the level of the herniated disk down to
the S1 vertebra displacing the dural sac dorsally. The mass was homogeneous and isointense
compared with cerebrospinal fluid (CSF). The patient was initially given a trial of
conservative management with analgesics and nerve root block. However, the response
was transient, and so a definitive surgery was planned. The patient underwent percutaneous
endoscopic interlaminar lumbar discectomy at L5-S1 from the left side. A cyst was
seen adjacent to the left posterior surface of the S1 vertebra, compressing the left
S1 nerve root dorsally [[Figure 2]]. Intraoperatively, we could identify the adhesions surrounding the discal cyst.
After meticulous dissection, the capsule was identified and so was the hard and inside
melting consistency material. After complete excision of disc, a rent was visible
in the underlying disc, which was the probable site of origin of the discal cyst.
Histopathology [[Figure 3]]a showed cyst wall devoid of epithelial lining and being formed by fibrocollagenous
tissue with focal myxoid areas and few areas of fibroblastic proliferation with inflammatory
cells. The patient had significant pain relief immediately after surgery and continues
to remain pain free at 6 months' follow-up.
Figure 1: Magnetic resonance imaging of case 1: (a) Sagittal T2-weighted image (left paramedian).
A small L5S1 herniated disc is seen. Just below the herniated disc, a cystic mass
is depicted with homogeneous high signal intensity. (b and c) Axial T2-weighted image
showing cystic lesion that displaces the dural sac and impinges on S1 nerve root.
(d-f) Postoperative T2 sagittal and axial images showing decompression and complete
excision of the cyst
Figure 2: (a) Intraoperative percutaneous endoscopic interlaminar lumbar discectomy image showing
the axillary area with discal cyst (1), S1 nerve root (2), and the dural sac (3).
(b) View after excising the capsule of cyst showing hard consistency lesion. (c) Melting
stage ruptured disc, visible after removing the hard consistency outer part. (d) Crater
of the ruptured disc: Clearing the operative field after moving the working channel
toward dorsal part of the intervertebral space, the crater within the ruptured disc
was exposed
Figure 3: (a) Histologic section of the cyst wall (hematoxylin and eosin) of case 1 showing
cyst wall devoid of epithelial lining and being formed by fibrocollagenous tissue
with focal myxoid areas and few areas of fibroblastic proliferation. (b) Histologic
section of the cyst wall (hematoxylin and eosin) of case 2 showing focal mucoid degeneration
with disc material mainly composed of nucleus pulposus
Case 2
A 54-year-old male presented with low back pain and right leg pain for 4 months. On
examination, SLRT was positive on the right side and had right ankle flexion weakness
of Grade 3 and great toe dorsiflexion weakness of Grade 1. MRI [[Figure 4]] depicted a small right-sided L4–L5 disc herniation and a cystic mass in the right
lateral aspect of the ventral extradural space from the level of the herniated disk
down to the L5 vertebra displacing the dural sac. The mass was homogeneous and isointense
compared with CSF. A discogram was performed which showed communication of cyst with
the underlying disc. Since the patient had already been on medications for the past
2 months, an option of definite surgery was given. A percutaneous endoscopic transforaminal
lumbar discectomy was performed at L4-L5 from the right side. The cyst was localized,
dissected carefully from surrounding and completely excised with partial discectomy.
The histopathology [[Figure 3]]b suggested focal mucoid degeneration with disc material mainly composed of nucleus
pulposus. The patient was relieved of pain immediately after surgery and continues
to be symptom free at 3 months of follow-up.
Figure 4: Magnetic resonance imaging of case 2. (a) Sagittal T2-weighted image (right paramedian)
showing a small L4-L5 herniated disc with underlying well-defined cystic mass with
homogeneous high signal intensity. (b and c) Axial T2-weighted image at the cranial
portion of the L5 level. The cystic lesion can be seen compressing the L5 nerve root
on the right side. (d-f) Postoperative T2 sagittal and axial images showing decompression
and excision of cyst
Discussion
Discal cysts, first described by Chiba et al.[[7]] in 2001, are believed to be originating from the disc material and a consequence
of degenerative changes. The pathology usually affects young adults, more commonly
males, and has a symptom complex similar to disc herniation and stenosis. The pathogenesis
of discal cyst remains unclear. Histopathological findings are predominantly fibrous
connective tissue without synovial lining cells.[[1]],[[3]],[[8]] Cyst content varies from serous to mucinous. Various different theories have been
proposed to explain the pathogenesis of discal cysts. While the vascular theory by
Chiba et al.[[7]] considers it to be a sequel of hemorrhage from epidural venous plexus, the more
recent degenerative theory by Kono et al.[[9]] discusses about the degenerative changes within disc. The resulting inflammation
causes the formation of a pseudomembrane with cystic softening of collagen. The spilling
of fluid from within the disc adds to it. Finally, in the chronic stage, a pseudocapsule
is formed with fibrous tissue and nonvascularized vessels, leading to adhesions in
the surrounding area.[[9]],[[10]]
MR imaging continues to be investigation of choice to diagnose discal cyst as it demonstrates
the nature of the cystic lesion and its relationship to the corresponding disc.[[7]],[[11]] Like a normal intervertebral disc, a discal cyst reveals a low signal on T1-weighted
imaging and a high signal on T2-weighted imaging. In addition, the surrounding rim
and contents of a cyst may show enhancement in a contrast-enhanced magnetic resonance
(MR). Other investigations for a suspected discal cyst may include discography and
computed tomography (CT) discography, which shows a flow of contrast into the cyst
through connective channels, which is pathognomic feature as it is not demonstrated
in intervertebral disc herniation and other intraspinal cysts.[[12]],[[13]],[[14]] We performed discography in both patients followed by MR. We advocate intraoperative
discography as it helps in identifying occasional hidden discal cysts as well as in
confirming complete excision.[[5]]
Various treatment modalities for discal cyst have been described. A close observation
in the initial period with analgesics is advised hoping for spontaneous resolution.
Conservative management as CT-guided aspirations and steroid administration have been
reported [[11]],[[15]],[[16]],[[17]] but a high recurrence rate precludes its widespread use. PELD is a minimally invasive
approach performed under local anesthesia without resection of bone or ligament.[[5]],[[18]] The operating time is short, and postoperative rehabilitation is fast. These advantages
make it the more preferable approach for discal cysts compared with other conventional
techniques.[[5]],[[17]]
Ha et al. suggested an additional partial discectomy to reduce the total volume of
nucleus pulposus and radiofrequency coagulation to make the nucleus pulposus more
stable. This procedure could help to prevent reherniation of nucleus pulposus, and
additional partial discectomy would prevent the postoperative discal pseudocyst occurrence.[[5]] Young et al. also supported complete excision of the pseudocapsule of cyst with
partial discectomy.[[19]] We believe excising any herniated part of disc is helpful to prevent similar symptoms
in future.
In our cases, we have excised the discal cyst by percutaneous endoscopic approach.
The adhesion between discal cyst and dura and disc material were severed, and the
vasculatures were coagulated. In order to prevent the recurrence, the stalk of the
cyst and its capsule were removed with an additional partial discectomy in both the
cases. This case report supports the degeneration theory of discal cyst.[[9]] We could witness the peudocapsule, the hard outer layer, melting consistency inner
part of cyst as well as crater in the underlying disc. The different pathological
components seen intraoperatively support its origin from resolution state of herniated
disc. We advocate endoscopic excision of discal cysts, as it provides the explicit
view of the pathology intraoperatively and helps in excision along with the capsule.
Any herniating fragment of the disc can be handled simultaneously. Meticulous dissection
along capsule to detether any adhesions, while safeguarding the nerve root remains
key to a successful endoscopy approach.
Conclusion
Despite numerous reports, the explicit pathophysiology of intraspinal discal cysts
remains obscure. Our endoscopic operative finding supports the origin of cystic membrane
by degenerative changes during the resolution stage of a herniated disc and is the
first report demonstrating different components of discal cyst in the endoscopic view.
Consent
Both the patients have given informed consent for submission of the manuscript.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form, the patients have given their consent for their images and other clinical
information to be reported in the journal. The patient understands that name and initials
will not be published and due efforts will be made to conceal identity, but anonymity
cannot be guaranteed.
