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Views: 0 Author: Site Editor Publish Time: 2026-07-21 Origin: Site
An intraosseous pneumatocyst is a rare benign cystic bone lesion characterized by the presence of gas within the bone. Unlike infectious or malignant bone lesions, intraosseous pneumatocysts usually remain asymptomatic and are most commonly discovered incidentally during radiographic examinations performed for unrelated conditions.
Since Ramirez et al. first described intraosseous pneumatocysts in 1984, an increasing number of cases have been reported. However, the exact pathogenesis of this uncommon lesion remains controversial. The most widely accepted hypothesis suggests that intraosseous pneumatocysts develop through the migration of gas from adjacent joints or intervertebral discs into the bone through microscopic channels caused by degenerative or mechanical changes.
Most reported intraosseous pneumatocysts occur in the pelvis, sacrum, and vertebral bodies, particularly in the cervical spine. In contrast, involvement of the scapula is extremely uncommon. To date, only isolated cases of scapular intraosseous pneumatocysts have been described.
This article presents a rare case of a scapular intraosseous pneumatocyst in a young adult male, highlighting the characteristic imaging findings and the importance of thin-slice computed tomography (CT) in identifying a subtle communication between the lesion and the glenohumeral joint.
Understanding these imaging characteristics is essential for orthopedic surgeons and radiologists to differentiate intraosseous pneumatocysts from more aggressive conditions, including osteomyelitis, osteonecrosis, and malignant bone tumors.
An intraosseous pneumatocyst is defined as a benign, gas-containing cystic lesion located inside bone tissue.
Unlike typical bone cysts containing fluid or soft tissue components, intraosseous pneumatocysts contain gas with attenuation values similar to air on CT scans. The gas component usually consists mainly of nitrogen, oxygen, and carbon dioxide.
Most patients do not experience specific symptoms. These lesions are often discovered accidentally during:
Trauma evaluation
Chest or shoulder imaging
CT examinations for unrelated diseases
Routine follow-up imaging
Because intraosseous pneumatocysts are uncommon and unfamiliar to many clinicians, they may initially raise concerns regarding:
Gas-forming osteomyelitis
Bone necrosis
Malignant bone lesions
Postoperative changes
Accurate imaging interpretation is therefore critical to avoid unnecessary invasive procedures.
Previous studies have demonstrated that intraosseous pneumatocysts preferentially occur near mobile joints or spinal segments subjected to mechanical stress.
Common locations include:
Ilium
Sacrum
Vertebral bodies
Facet joints
Sacroiliac joints
The high frequency of these locations supports the theory that repetitive mechanical stress and joint degeneration contribute to gas migration into adjacent bone.
The scapula is rarely affected by intraosseous pneumatocysts.
Possible explanations include:
Limited occurrence of degenerative changes in the scapular region
Complex anatomy of the glenohumeral joint
Difficulty detecting very small communication channels between the joint and bone
Previous reports suggest that standard CT scanning may fail to identify these tiny pathways because conventional slice thickness can obscure small cortical defects.
Therefore, advanced imaging techniques such as:
Thin-slice CT
Multiplanar reconstruction (MPR)
may play an important role in revealing the true origin of these lesions.
A 37-year-old man with no significant medical history was admitted to the intensive care unit for airway monitoring due to an acute respiratory condition.
During routine chest radiography, an incidental abnormality was identified in the left shoulder region.
The patient reported:
No shoulder pain
No history of trauma
No limitation of shoulder movement
Physical examination revealed no abnormalities of the musculoskeletal system.
Figure 1 Left shoulder X-ray examination. (A) Anteroposterior view, (B) Grashey view, and (C) lateral view show a lucent lesion in the subchondral bone of the infraglenoid region of the scapula.
Dedicated shoulder radiographs demonstrated:
A well-defined radiolucent lesion
Multiloculated appearance
Location beneath the glenoid region of the scapula
The lesion showed:
Smooth margins
No periosteal reaction
No cortical destruction
No pathological fracture
These characteristics suggested a benign bone lesion rather than an aggressive pathological process.
Computed tomography (CT) is considered the most valuable imaging modality for diagnosing intraosseous pneumatocysts because it can accurately identify gas density within bone.
In this case, a non-enhanced CT examination was performed using 0.625 mm thin-slice axial scanning, allowing detailed evaluation of the lesion morphology and surrounding bone structures.
CT demonstrated a:
Well-defined osteolytic lesion
Located in the subchondral bone beneath the glenoid cavity
Measuring approximately 21 × 19 × 19 mm
With smooth cortical margins
Without bone destruction or aggressive characteristics
The lesion showed mixed internal components:
Peripheral gas density area: approximately -875 HU
Internal fluid density component: approximately 15 HU
The presence of gas attenuation within the bone lesion was highly suggestive of an intraosseous pneumatocyst.
Figure 2 Non-contrast CT examination of the left shoulder. (A) Axial, (B) coronal, and (C) sagittal views show a well-defined lucent lesion in the subchondral bone of the infraglenoid region of the scapula, with gas-density shadow visible laterally and scattered fluid-density shadow medially. Oblique reformatted image (D) prominently displays a tiny cortical defect (white arrow) at the posteroinferior glenoid rim, suggesting communication between the lesion and the glenohumeral joint space.
One of the most important findings in this case was the identification of a subtle cortical defect connecting the lesion with the glenohumeral joint.
Using multiplanar reconstruction (MPR), especially oblique reconstruction images, a small cortical interruption was identified at the posteroinferior glenoid margin.
This finding suggested a possible pathway through which intra-articular gas migrated into the subchondral bone.
The discovery of this tiny communication provides important imaging evidence supporting the theory that intraosseous pneumatocysts originate from adjacent joint spaces rather than spontaneous gas production inside bone.
The communication between the joint cavity and intraosseous pneumatocyst is often extremely small.
Conventional CT examinations using thicker slices (2–3 mm) may fail to identify these tiny cortical channels because of:
Partial volume effects
Limited spatial resolution
Overlapping anatomical structures
In contrast, thin-slice CT (≤1 mm slice thickness) provides:
Higher spatial resolution
Better cortical evaluation
Improved detection of subtle bone defects
Previous reports of scapular intraosseous pneumatocysts using thicker CT slices failed to demonstrate communication with the glenohumeral joint.
This case suggests that the absence of visible communication in previous studies may have been related to imaging limitations rather than true absence of a connecting pathway.
Magnetic resonance imaging (MRI) was performed for further evaluation.
The lesion demonstrated:
Multiple well-defined high-signal areas on T2-weighted sequences
Internal air-fluid levels
No fat component
Susceptibility artifacts caused by gas accumulation
The gas component produced characteristic magnetic susceptibility effects, corresponding to the gas identified on CT.
Figure 3 Left shoulder MRI examination. (A) Proton density fat-suppressed axial, (B) T2-weighted gradient-echo axial, (C) proton density sagittal, and (D) T2-weighted fat-suppressed sagittal sequences. Multiple gas-fluid levels are demonstrated, with no evidence of fat signal within the lesion.
Figure 4 Left shoulder MRI examination. (A) T1-weighted axial, (B) T1-weighted fat-suppressed contrast-enhanced axial, (C) T1-weighted coronal, and (D) T1-weighted fat-suppressed contrast-enhanced coronal sequences. No enhancing component is identified within the lesion.
On:
T1-weighted imaging
T1-weighted fat-suppressed enhanced sequences
the lesion showed:
No internal enhancement
No surrounding soft tissue mass
No inflammatory infiltration
These findings further supported the diagnosis of a benign intraosseous pneumatocyst.
Although intraosseous pneumatocysts are benign lesions, their imaging appearance may overlap with several clinically important conditions.
Accurate differentiation is essential.
Gas-forming osteomyelitis is a serious infectious condition that requires urgent treatment.
However, unlike intraosseous pneumatocysts, infection usually presents with:
Fever
Elevated inflammatory markers
Local pain
Systemic symptoms
Ill-defined bone destruction
Extensive marrow edema
Abscess formation
Soft tissue inflammation
In contrast, intraosseous pneumatocysts typically demonstrate:
Well-defined margins
No inflammatory changes
No aggressive bone destruction
Incidental discovery
Some bone tumors may present as radiolucent lesions.
However, malignant lesions usually show:
Irregular margins
Cortical destruction
Periosteal reaction
Soft tissue extension
The absence of these findings strongly favors a benign intraosseous pneumatocyst.
Bone necrosis may sometimes demonstrate internal gas, particularly in advanced cases.
However, osteonecrosis usually presents with:
Structural collapse
Sclerotic changes
Irregular bone architecture
The smooth, well-defined appearance of an intraosseous pneumatocyst helps distinguish it from osteonecrotic lesions.
The diagnosis of scapular intraosseous pneumatocyst should be considered when imaging demonstrates:
✓ Well-defined cystic lesion within bone
✓ Gas attenuation values similar to air
✓ Possible fluid component
✓ No aggressive bone destruction
✓ Possible communication with adjacent joint space
✓ High signal intensity on fluid-sensitive sequences
✓ Air-fluid levels
✓ Susceptibility artifacts caused by gas
✓ No enhancement after contrast administration
Recognizing these characteristic findings can prevent unnecessary biopsy or surgical intervention.
The exact mechanism responsible for the development of intraosseous pneumatocysts remains controversial. However, the most widely accepted theory is that these lesions are caused by gas migration from adjacent joints or intervertebral discs into bone through microscopic channels.
This mechanism is closely related to the vacuum phenomenon, a process in which gas forms within a joint space or intervertebral disc due to reduced pressure.
The vacuum phenomenon commonly occurs during:
Joint distraction
Degenerative changes
Repetitive mechanical loading
Segmental instability
Nitrogen-rich gas produced within the joint cavity may gradually enter the adjacent subchondral bone through small cortical defects, resulting in the formation of an intraosseous pneumatocyst.
Several findings support the hypothesis that intraosseous pneumatocysts originate from adjacent joint spaces.
Intraosseous pneumatocysts are rarely found randomly throughout the skeleton.
They are most commonly located adjacent to:
Sacroiliac joints
Facet joints
Intervertebral discs
Hip joints
Shoulder joints
This distribution strongly suggests that mechanical communication between joints and bone plays an important role.
Many reported cases occur in older patients with:
Osteoarthritis
Degenerative disc disease
Joint instability
Degenerative changes may create microscopic defects in the subchondral bone, allowing gas migration from the joint cavity.
A systematic review by Oehler et al. analyzed previously reported cases and found that intraosseous pneumatocysts were more frequently observed in middle-aged and elderly males, supporting the relationship between mechanical stress and degenerative changes.
The strongest evidence comes from modern imaging techniques.
Previous studies using conventional CT often failed to identify direct communication between intraosseous pneumatocysts and adjacent joints.
However, studies using thin-slice CT demonstrated a higher detection rate of these tiny channels.
In the present case, ultra-thin CT scanning with a slice thickness of 0.625 mm revealed a subtle cortical defect connecting the scapular lesion with the glenohumeral joint.
This finding provides direct radiological evidence supporting external gas migration from the joint cavity.
An interesting feature of this case is that the patient was relatively young:
Age: 37 years
No history of shoulder trauma
No degenerative glenohumeral joint disease
This raises an important question:
Can intraosseous pneumatocysts develop without obvious joint degeneration?
The answer appears to be yes.
Although degenerative disease is commonly associated with intraosseous pneumatocysts, several cases have been reported in younger patients without significant abnormalities.
Possible explanations include:
Repeated low-energy mechanical stress or previous unnoticed trauma may produce microscopic cortical defects.
These defects may later serve as pathways for gas migration.
Some researchers have proposed that congenital anatomical variations may contribute to the development of intraosseous pneumatocysts.
Subtle structural differences in the bone-joint interface may create a predisposed pathway for gas accumulation.
The vacuum phenomenon does not always require advanced degeneration.
Transient changes in joint pressure caused by:
Shoulder movement
Mechanical loading
Joint distraction
may generate gas formation and migration even in otherwise healthy joints.
In most cases, intraosseous pneumatocysts are considered benign lesions with a stable clinical course.
Most patients:
Have no symptoms
Require no treatment
Only need imaging observation
Histological studies have shown that some lesions consist of:
Fibrous connective tissue
Nonspecific fibrous membranes
Minimal inflammatory changes
These findings further support their benign nature.
Although most lesions remain stable, enlargement has occasionally been reported.
A few cases involving vertebral intraosseous pneumatocysts demonstrated progressive expansion.
In rare situations, enlargement may cause:
Spinal canal narrowing
Nerve compression
Neurological symptoms
For example, an enlarging cervical vertebral intraosseous pneumatocyst has been reported to cause spinal cord compression requiring surgical treatment.
However, such complications are extremely uncommon.
Although the defining feature of intraosseous pneumatocysts is gas accumulation, some lesions may also contain fluid components.
In this case, CT and MRI demonstrated:
Gas component
Fluid component
Air-fluid levels
The mechanism of fluid accumulation remains unclear.
Several hypotheses have been proposed:
Changes in pressure between the cyst cavity and surrounding bone marrow may allow fluid accumulation over time.
Ramirez initially suggested that some intraosseous pneumatocysts may originate from pre-existing fluid-containing lesions, including:
Simple bone cysts
Ganglion cysts
Synovial cysts
Gas migration into these lesions may later produce a mixed gas-fluid appearance.
This case provides several important clinical insights:
The identification of a microscopic communication between the scapular lesion and the glenohumeral joint highlights the importance of high-resolution imaging.
Thin-slice CT may improve diagnostic accuracy and provide valuable information regarding disease mechanisms.
When a well-defined gas-containing bone lesion is identified, clinicians should consider intraosseous pneumatocyst as a possible diagnosis.
Correct recognition can prevent:
Unnecessary biopsy
Excessive imaging examinations
Patient anxiety
Misdiagnosis as infection or malignancy
Although scapular involvement is extremely rare, the same imaging principles apply.
Orthopedic surgeons and radiologists should recognize that intraosseous pneumatocysts can occur in unusual skeletal locations.
Because intraosseous pneumatocysts are rare and may mimic other bone lesions, a systematic diagnostic approach is recommended.
The first step is to determine whether the lesion is associated with clinical symptoms.
Important factors include:
Local pain
Previous trauma
Infection history
Cancer history
Recent surgery
Systemic inflammatory symptoms
Most intraosseous pneumatocysts are found incidentally in asymptomatic patients.
A lack of systemic symptoms and normal physical examination findings strongly support a benign lesion.
Radiographs are often the first imaging examination that reveals the lesion.
Typical X-ray findings include:
Round or oval radiolucent lesion
Well-defined margins
Subchondral location
No periosteal reaction
No cortical destruction
Although X-rays can suggest the diagnosis, they cannot reliably confirm the presence of gas.
CT is the most important diagnostic tool.
Characteristic CT findings include:
Gas attenuation within the bone lesion
Air density close to -1000 HU
Smooth cortical boundary
Possible communication with adjacent joint space
Thin-slice CT with multiplanar reconstruction is particularly valuable because it can identify small cortical channels that may not be visible on conventional imaging.
MRI is usually not required for diagnosis but may be performed when:
The lesion appearance is atypical
Tumor or infection cannot be excluded
Soft tissue involvement needs evaluation
Typical MRI findings include:
Signal void caused by gas
Air-fluid levels
No enhancement after contrast
No surrounding inflammatory reaction
In most cases:
No treatment is required.
Because intraosseous pneumatocysts are benign lesions, management usually consists of:
Clinical observation
Imaging follow-up when necessary
Patient reassurance
Surgical intervention is rarely indicated.
Further investigation may be necessary if imaging demonstrates:
Progressive enlargement
Persistent unexplained pain
Cortical destruction
Soft tissue extension
Aggressive imaging characteristics
In these situations, clinicians should exclude alternative diagnoses such as:
Infection
Primary bone tumors
Metastatic lesions
Osteonecrosis
An intraosseous pneumatocyst is a rare benign bone lesion containing gas inside the bone. It is usually discovered accidentally during imaging examinations and typically does not cause symptoms.
No.
An intraosseous pneumatocyst is not a tumor. It is considered a benign cyst-like lesion related to gas accumulation within bone tissue.
Unlike malignant tumors, it usually shows:
Smooth borders
No bone destruction
No soft tissue mass
No aggressive growth pattern
The most accepted explanation is that gas migrates from nearby joints or intervertebral discs through tiny bone channels created by mechanical stress or degenerative changes.
This process is associated with the vacuum phenomenon.
Some lesions may remain unchanged for years, while others may gradually transform.
Reported changes include:
Reduction of gas content
Increased fluid components
Replacement by fibrous tissue
However, most lesions remain clinically insignificant.
Generally, no.
A scapular intraosseous pneumatocyst without symptoms or aggressive imaging findings usually requires only observation.
Surgery is considered only when:
The diagnosis is uncertain
The lesion enlarges significantly
Symptoms are directly related to the lesion
✓ Intraosseous pneumatocyst is a rare but benign gas-containing bone lesion.
✓ The scapula is an extremely uncommon location.
✓ CT is the most reliable imaging method for diagnosis.
✓ Thin-slice CT can reveal tiny communications between the lesion and adjacent joints.
✓ A well-defined gas-containing lesion without aggressive features should suggest intraosseous pneumatocyst.
✓ Correct diagnosis helps avoid unnecessary biopsy and invasive treatment.
Scapular intraosseous pneumatocyst is an extremely rare benign bone lesion that may be mistaken for more serious pathological conditions.
In this case, high-resolution CT demonstrated a tiny cortical communication between the lesion and the glenohumeral joint, providing additional evidence that intraosseous pneumatocysts may originate from gas migration through joint-related pathways.
Although uncommon, awareness of the characteristic imaging findings is essential for orthopedic surgeons and radiologists. Recognition of this benign entity can prevent unnecessary diagnostic procedures and improve patient management.
With the continuous development of advanced imaging techniques, particularly thin-slice CT and multiplanar reconstruction, more cases of intraosseous pneumatocysts may be accurately identified, further improving our understanding of this fascinating but uncommon condition.
