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Abstract:
Introduction: Cervical Pneumatocyst is an important entity that has been rarely reported in the literature. Less than 20 cases have been reported in the English literature. This entity is an important differential consideration when evaluating cervical spine lesions. The purpose of our study is to characterize the imaging features of cervical pneumatocysts.
Methods: We report a case of a cervical pneumatocyst in a 51 year old female which mimicked a sclerotic lesion on MR evaluation. Additionally, a dedicated literature review was performed evaluating the location, signal alterations, and imaging characteristics of sixteen cervical pneumatocysts.
Results: Fifteen of the sixteen cases in the cervical spine were found in the vertebral body. One case was identified in the lateral mass of the cervical spine. Two pneumatocysts were identified in C4, eight in C5, four in C6 and one in C7. Nine of the sixteen cases demonstrated disruption of the endplate with likely communication with either the spinal canal or intravertebral disc with the remaining seven cases appearing isolated from the vertebral body.
Conclusions: Cervical pneumatocysts are benign lesions that do not require urgent treatment. Based on their imaging appearance alone, they can be differentiated from more serious lesions such as neoplasms or osteomyelitis.
J.Orthopaedics 2011;8(1)e8
Keywords:
Spine; Pneumatocyst; Sclerotic Lesion J.Orthopaedics 2011
Introduction:
Intravertebral gas or pneumatocyst is an uncommon finding which has been the subject of several case reports to date. It’s exact etiology is unclear, but has been reported in association with vertebral collapse from osteonecrosis, infection, trauma and spondylosis (1-2). Pneumatocysts are most commonly seen within the ilium and sacrum immediately adjacent to the sacroiliac joint (3). Less than 30 cases have been reported in the vertebral body (4-18). We describe a case of an enlarging cervical pneumatocyst which initially was concerning for a sclerotic lesion due to signal characteristics on magnetic resonance imaging (MRI) but was diagnostic for a pneumatocyst on further evaluation with multi-detector computed tomography (CT).
Case
Report:
A 51-year-old female presented with worsening neck pain for several years. She denies any numbness or paresthesia consistently in the upper extremities, but reports occasional moments of numbness and paresthesia in the arms. On neurological evaluation, bilateral strength and sensation were intact in the extremities. Laboratory evaluation and past medical history were unremarkable. An MRI evaluation 8 years prior demonstrated multilevel degenerative and spondylitic changes but no focal osseous lesion or central canal narrowing. A CT examination 5 years ago showed multilevel degenerative changes with a small air-containing lesion in the left lateral aspect of C7 adjacent to the endplate. Given the patient’s persistent pain, a repeat MRI was performed which demonstrated moderate cervical stenosis from C4/C5 to C6/C7 with multilevel degenerative and spondylitic changes. A focal osseous lesion was seen within the left lateral aspect of the C7 vertebral body with low signal characteristics on T1 and T2-weighted images (Figure 1a-b). As there was concern that this might represent a sclerotic lesion, further evaluation with CT imaging was performed. On CT evaluation, a well-defined cystic lesion measuring 1.3x1.3x0.9 cm within the left posterolateral aspect of C7 was identified (Figure 2a-b). Lesion had Hounsfield attenuation coefficients consistent with air, and findings were diagnostic for a vertebral body pneumatocyst. Additional gas was seen within the intervertebral disc space along with multilevel degenerative changes. The patient was started on analgesics and physical therapy with improvement of symptomatology and stability on clinical evaluation. Six month follow-up CT imaging demonstrated no significant change in size or location of the vertebral body pneumatocyst.
Figure 1a: Saggital T1 weighted image demonstrating a low signal osseous focus in the posterolateral aspect of the C7 vertebral body superimposed on multilevel degenerative and spondylotic changes.
Figure 1b: Saggital T2 weighted image demonstrating a low signal osseous focus in the posterolateral aspect of the C7 vertebral body superimposed on multilevel degenerative and spondylotic changes.
Figure 2a: Axial CT image through the C7 vertebral body demonstrates gas attenuation in the left posterolateral aspect of the C7 vertebral body.
Figure 2b: Sagittal reconstructed image through the cervical spine demonstrating gas attenuation within the posterior C7 vertebral body. Note the extension to the intervertebral disc space (arrow).
Discussion:
Less than 30 cases of intravertebral pneumatocysts have been reported in the English literature with only 16 cases involving the cervical spine (4-18). Fifteen of the sixteen cases in the cervical spine were found in the vertebral body (4-5, 7-8, 10-11, 13-18), and one case identified in the lateral mass of the cervical spine (9). Two pneumatocysts were identified in C4 (13, 16), eight in C5 (7-8, 11, 13-15, 17-18), four in C6 (5, 10, 15, 17) and one in C7 (4). Nine of the sixteen cases demonstrated disruption of the endplate with likely communication with the spinal canal or intervertebral disk (4-5, 10, 13, 15-17) and the remaining seven cases appeared isolated within the vertebral body (7-9, 11, 14, 18).
The exact etiology of pneumatocyst remains unclear. Ramirez et al. (3) hypothesized that the mechanism was related to gas accumulation in a simple fluid-filled cyst or ganglion, while Laufer et al (9) suggested that the accumulation was nitrogen from adjacent joints. More recent reports suggest that nitrogen gas that is found in degenerative intervertebral disks, known as “vacuum disk phenomenon” (19), likely extends through end-plate defects into the vertebral body (15-17). However, there are cases of pneumatocysts that do not demonstrate a communication between the endplate and the vertebral body, and do not have significant spinal degeneration (4, 9, 18). These findings have lead to the suggestion that there are two distinct types of intravertebral pneumatocysts; a degenerative pneumatocyst is typically larger and found in older individuals with spinal degeneration, and non-degenerative pneumatocyst is smaller and seen in a younger population without significant degenerative changes (15-18). We believe that both types
of pneumatocysts likely result from a disruption in the endplate either from a degenerative etiology or from a remote traumatic or congenital abnormality.
Our case illustrates the typical appearance of a degenerative pneumatocyst and its potentially confusing appearance on MR evaluation. A hypointense T1 and T2 signal bone lesion is concerning for sclerosis and must be further evaluated with conventional radiography or CT (18). Occasionally on MR imaging, susceptibility artifact from the air containing pneumatocyst can suggest the diagnosis (10). CT is the most useful modality for diagnostic purposes demonstrating the characteristic air attenuation of the pneumatocyst (5). No contrast enhancement is seen on MR or CT evaluation (16).
Although pneumatocysts can be large lesions, our case being the largest reported in the literature, their clinical course is benign. Pneumatocysts have been reported to remain stable in size for years (10) and have also been seen to enlarge (15). Our case demonstrates a pneumatocyst that was new from the prior MRI (2002) but was seen as a small focus on the more recent prior CT (2005), and then presented as a larger lesion seen on the current CT and MRI (2010). These findings indicate that pneumatocysts evolve over time. Five cases of vertebral pneumatocysts have been reported to spontaneously progress to fluid-filled cysts within 2-16 months from the initial findings (11, 14, 17) with one case being replaced with granulation tissue at 40-weeks after follow-up (14).
In summary, cervical pneumatocysts are benign lesions that do not require urgent treatment. Based on their imaging appearance alone they can be differentiated from the more worrisome bone neoplasms and osteomyelitis. Pneumatocysts may communicate
through small defects in the vertebral endplates with the intervertebral disc space or the spinal canal. Pneumatocysts can enlarge over time and can progress to fluid-filled cysts.
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