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Age / Sex : 34 / F
Age / Sex: 34/F
Chief complaint: Back pain
1) What is your impression?
Two weeks later, you can see the final diagnosis with a brief discussion of this case.
* Send Application Answers to Ja-Young Choi, MD (drchoi01@gmail.com)
Courtesy: Soo-Jung Choi, MD. Gangneung Asan Hospital
Diagnosis: extradural arachnoid cyst
Discussion
Findings:
T2- and T1 weighted sagittal and T2 weighted axial MR images show elongated cystic lesion in posterior epidural space. The lesion abuts the posterior epidural fat cranially and caudally. There is no epidural fat directly posterior to the lesion, indicating that the lesion is extradural. Dural sac and spinal cord is displaced and flattened. The lesion is not enhanced after Gd-enhancement and the signal intensity is same with CSF. CT after myelography demonstrates contrast filling in the posterior epidural cyst, indicating direct communication with the subarachnoid space.
Differential Diagnosis:
intradural arachnoid cysts, neurenteric cysts, perineural cysts, synovial cysts, meningocele, cystic neoplasms, congenital and traumatic epidermoid, dermoid, inflammatory cysts and cysticerosis
Diagnosis: Extradural arachnoid cyst (extradural meningeal cyst type IA)
Discussion:
Extradural arachnoid cysts in the spine are rare and are seldom a cause of spinal cord compression. They are thought to arise from congenital defects in the dura mater, and they almost always communicate with the intrathecal subarachnoid space through a small defect in the dura. The mechanism of enlargement is supposed to be related to a one-way valve effect at the neck of the diverticulum. Extradural arachnoid cysts most commonly occur in the middle to lower thoracic spine (65%) but also have been reported in the lumbar and lumbosacral (13%), thoracolumbar (12%), sacral (7%), and cervical regions (3%). The cause of these cysts has not been determined definitively, although they most probably have a congenital origin. Some may be acquired from trauma, infection, or inflammation. Magnetic resonance imaging is useful in detecting the mass, and the signal characteristics are consistent with those of CSF. Computed tomography myelography is better for detecting the dural defect when communication between the cyst and the subarachnoid space occurs and thus allows accurate diagnosis of these lesions. The most common presenting symptoms are pain and progressive spastic or flaccid paraparesis, often asymmetrical. Symptomatic cysts are primarily treated with excision and obliteration of the communicating dural defect.
Classification for spinal meningeal cysts by Nabors et al. (AJR 2002;178:201-207)
Type 1—Extradural Meningeal Cysts Containing No Neural Tissue
Type 1 cysts can be subdivided into extradural arachnoid cysts (type 1A) and sacral meningoceles (type 1B). Type 1A cysts probably arise from the herniation of the arachnoid through congenital or acquired dural defects. The cysts begin as diverticula and subsequently enlarge, possibly because of a valvelike mechanism. Postural changes and Valsalva's maneuver may produce symptoms. These cysts usually arise in the mid-to-lower thoracic spine, often at the junction of the meninges and the dorsal nerve root sleeves proximal to the dorsal root ganglia. Type 1A lesions most commonly project dorsally and may partially protrude into the adjacent neural foramen. "Arachnoid cyst" is a histologic diagnosis, and the cyst has either no epithelial lining or an attenuated lining of arachnoidlike cells. In the imaging literature, the terms "arachnoid cyst" and "meningeal cyst" are used interchangeably. The origin and pathogenesis of sacral meningoceles (type 1B) are uncertain, but association of the entity with other spinal anomalies suggests a congenital origin. These arachnoid diverticula usually present in the third or fourth decade of the patient's life and cause nonspecific symptoms such as lower back pain that increases with activity or Valsalva's maneuver (in 80% of patients) and perineal paresthesia (in 50% of patients).
Type 2—Extradural Meningeal Cysts Containing Neural Tissue
These extradural meningeal cysts contain either nerve roots (i.e., perineurial cysts or Tarlov cysts) or, in some cases, herniated spinal cord. Cysts containing spinal nerve root fibers typically arise in the perineurial space between the endoneurium (continuous with the pia mater) and the perineurium (derived from the arachnoid membrane). These cysts usually occur in the lower spine distal to dorsal root ganglia. A cyst may contain neural tissue, nerve cell bodies, and, occasionally, evidence of an old hemorrhage in its cavity or wall. Symptomatic cysts are excised surgically. Simple aspiration is unsatisfactory because the cysts tend to refill. MR imaging shows the cysts as hyperintense fluid collections on T2-weighted images. In rare cases of spinal cord herniation, the cord may appear atrophic and acutely angled into the meningeal defect on sagittal images. Intrathecally administered contrast material usually fills the cyst easily
Type 3—Intradural Meningeal Cysts
Intradural meningeal cysts consist of loculations of the arachnoid that may cause symptomatic compressive myelopathy. Most of the cysts communicate with the subarachnoid space through a narrow neck. Congenital lesions are virtually always posterior to the cord and are probably related to the septum posticum of Schwalbe, which divides the dorsal subarachnoid space in the midline from the cervical to the lumbar region. Suggested explanations include congenital weakness in the arachnoid, causing bulging in response to variations in cerebrospinal fluid pressure or possibly hypertrophic proliferation and dilatation of arachnoid granulation. Acquired intradural cysts may be anterior, posterior, or lateral to the spinal cord. These acquired intradural arachnoid cysts arise from arachnoiditis caused by trauma, hemorrhage, or inflammation. Associated findings of arachnoiditis may also be seen. The thoracic spine is most commonly affected. On CT myelography, communicating cysts usually opacify with contrast material. Noncommunicating cysts present as intradural—extramedullary masses that may block uptake of contrast material during myelography. T2-weighted MR images may show a heterogeneous signal attributable to the flow effect in the cyst fluid. The signal in the cyst may be higher than that of the cerebrospinal fluid because of the relative dephasing of the protons in the pulsatile cerebrospinal fluid or the higher protein content of the cyst fluid.
References:
1. Congia S, Coraddu M, Tronci S, Nurchi G, Fiaschi A. Myelographic and MRI appearances of a thoracic spinal extradural arachnoid cyst of the spine with extra- and intraspinal extension. Neuroradiology 1992;34:444-446
2. Khosla A, Wippold FJ II. CT myelography and MR imaging of extramedullary cysts of the spinal canal in adult and pediatric patients. AJR 2002;178:201-207
3. Rimmelin A, Clouet PL, SalatinoS, Kehrili P, Maitrot D, Sephan M, Dietemann JL. Imaging of thoracic and lumbar spinal extradural arachnoid cysts; report of two cases. Neuroradiology 1997;39:203-206
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