Full endoscopic treatment of unusual spontaneous degenerative epidural cyst: A case report.

BACKGROUND: Extensive studies have been performed about the synovial cyst and intraspinal extradural ganglion cyst. Here, we describe a new type of the cyst with entirely different histological characteristics, which we are now calling a "Spontaneous Degenerative Epidural Cyst." CASE DESCRIPTION: A 74-year-old male presented with low back pain, bilateral lower extremity radiculopathy, and a cauda equina syndrome. He exhibited a partial left foot drop (Grade 3/5) and hypoesthesia in the sacral region. The magnetic resonance imaging (MRI) showed two cysts at the L4-L5 level; Cyst I was in the left foramen and Cyst II was within the epidural space between the dura and ligamentum flavum. Cyst I was removed through an endoscopic transforaminal approach; it originated from the left facet joint and with synovial lining was confirmed to be a synovial cyst. Cyst II required an endoscopic interlaminar approach, and pathology revealed granulation tissue with micro-calcification, woven bone formation, hemosiderin pigment, and focal cystic change consistent with our designation "Spontaneous Degenerative Epidural Cyst."
CONCLUSION: "Spontaneous Degenerative Epidural cyst" should be considered among the differential diagnostic consideration for the different lumbar cysts. High-resolution MRI is the most useful in diagnosing these lesions, while full endoscopic treatment provides for adequate resection of these lesions.

INTRODUCTION

We have identified a unique type of intraspinal lumbar cyst, which we termed a “Spontaneous Degenerative Epidural Cyst,” located between the ligamentum flavum and dura. It was a distinctive feature since the connection was neither to the ligamentum flavum nor dura and it exhibited unique histological characteristics.

CASE REPORT

A 74-year-old male with 6-month history of lower extremity radiculopathy, acutely presented with a cauda equina syndrome. On examination, he had a left-sided partial foot drop (extensor hallucis longus dorsiflexion 3/5) and sacral hypoesthesia. The magnetic resonance (MR) imaging showed severe L4–L5 stenosis, and two lumbar cysts: cyst I was located in the left foramen, while Cyst II was situated between the dura and ligamentum flavum; there was no evidence of instability [Figures 1 and 2]. A transforaminal endoscopic approach revealed that cyst I was attached to the left facet joint; indeed, it proved to be a synovial cyst [Figure 3]. A full endoscopic interlaminar approach was utilized to excise cyst II; this huge epidural cyst with marked adhesions was not connected to either the ligamentum flavum or the dura [Figure 4]. [Video 1]. Postoperatively, the patient had immediate pain relief and remained asymptomatic 6 months later [Figure 5].

Figure 1:

Preoperative magnetic resonance imaging showing location of epidural (a,b) and foraminal (c) cysts which are hyperintense on T2 weighted images.

Figure 2:

Preoperative X-ray lateral neutral (a), flexion (b), and extension (c) views without any evidence of instability.

Figure 3:

Intraoperative images showing huge foraminal cyst I (In circle).

Figure 4:

Intraoperative images showing: (a) Huge intraspinal epidural cyst II (In circle) not attached to ligamentum flavum or dura. (b) Sever adhesion between the ligamentum flavum and dura mater. (c) Free dura after cyst removal.

Figure 5:

Magnetic resonance imaging on 1st postoperative day revealed no residual pathology and adequate decompression on T2-weighted sagittal (a) and axial (b,c) images at the L4–L5 level.

Histology

Cyst I originated from the facet joint and had a synovial lining consistent with a synovial cyst. The “Spontaneous Degenerative Epidural Cyst II,” located in the epidural space between the dura and the ligamentum flavum, showed granulation tissue with microcalcifications, woven bone formation, hemosiderin pigmentation, and focal cystic changes [Figure 6].

Figure 6:

Microscopic sections (a-40×, b-100×, c-400×) showing granulation tissue with microcalcifications, woven bone formation, hemosiderin pigments, and focal cystic changes. The lining epithelium of cystic component is denuded.

DISCUSSION

Lumbar intraspinal cysts can be either intradural or extradural [Table 1]. Intradural cysts are either arachnoidal or endodermal (enterogenous).[4] Epidural/extradural cysts are classified anatomically or pathologically, according to the anatomical structure(s) of origin, namely herniated disc cyst, facet joint cyst, ligamentum flavum cyst, and posterior longitudinal ligament cyst [Figure 7].[1,2] Pathologically, degenerative epidural/extradural cysts are classified as synovial cysts or non synovial ganglion cysts. Lake et al.[3] also described spinal epidural cysts as arachnoidal herniations through congenital or traumatic dural defects. Other theories consider these lesions: (1) hamartomatous distensions of spinal arachnoid villi or (2) valve-like pouches on the dorsal aspect of the thoracic subarachnoid space which may become distended and have very small or no communication with the subarachnoid space.[3]

Table 1:

Types of intraspinal cyst.

Figure 7:

Different types of spinal cysts and their locations: (1) Vacuum cyst, (2) discal cyst, (3) facet cyst, (4) posterior longitudinal ligament cyst, (5) ligamentum flavum cyst, (6) foraminal cyst, (7) spontaneous degenerative epidural cyst.

In our patient with two cystic lesions, cyst I was a synovial cyst. Intraoperative and histological findings of cyst II did not, however, fit in the typical categories of synovial or ganglion cysts. Rather, cyst II with calcification, granulation tissue, and hemosiderin deposits reflected a degenerative process involving the central lumbar canal that we newly called a “Spontaneous Degenerative Epidural Cyst.”

CONCLUSION

Here, we report on a “Spontaneous Degenerative Epidural Cyst” involving the lumbar spinal canal. It should be considered among the differential diagnoses for lumbar cysts and is best diagnosed on MR. Full endoscopic resection provides symptomatic relief and pathological confirmation.