Osteoma of paranasal sinuses

Introduction:
Sinonasal osteomas are common entity seen in patients.  Rhinosinus osteomas are commonly asymptomatic and are incidental findings on imaging studies.

History:
Viega was the first to document sinus osteoma in 1506. 
In 1733, Vallisnieri described frontal sinus osteoma that protruded into the brain.

Epidemiology:

Ostomas are the most common benign tumors of paranasal sinuses.

This condition is more common in males.
It is common in patients  between their second and third decades of life.

Etiology:

Three accepted theories of etiology of osteomas are:
1. Developmental
2. Traumatic
3. Infectious

Developmental theory:
This theory is based on the concept that adult tissues contain embryonic remnants which usually lie dormant.  These remnants gets activated to become a neoplasm. 
The ethmoid bone is formed by endochondral bone formation, where as the frontal bone is ossified by membranous pathway.  This theory implies that the apposition of membranous
and endochondral bones traps some of these embryonic cells eventually leading to unchecked osseous proliferation.  This could be the reason for the common occurrence of
osteomas near the fronto ethmoidal suture lines.  It goes without saying that osteomas in other areas could not be accounted by this theory.

Traumatic theory:
This theory relies on the inflammatory process as the initiating force for tumor formation.  It has been postulated that bony trauma could be the root cause
for osteoma formation.  It has been pointed out by Sayan et al that osteomas arising from the mandible have a predilection for places where muscles insert on the bone.  Even a minor trauma may incite inflammtory process subperiosteally in these bones.  Inflammation along with constant traction applied by the attached musculature could lead to
osteoma formation.  This could also account for the reported male preponderance in osteomas.

Infectious theory:

This theory suggests that osteitis resulting from chronic infections could lead to osteoma formation in paranasal sinuses.

Pathology:

The osteoma could be smooth and lobulated.  It could be either sessile / pedunculated.  Usually it is covered by intact sinus mucosa.  Histologically speaking
there are three types of osteomas.    They are:
1. Ivory / compact osteoma: Otherwise also known as eburnated osteoma.  In this type of osteoma the bone is very dense and lacks haversian canals.  These
osteomas develop from membranous elements.

2. Osteoma spongiosum: Also known as mature osteoma is composed of softer bone.  This type of osteomas are known to arise from cartilagenous elements.
These osteomas have little medullary component containing fibrofatty tissue.

3. Mixed osteoma: This type contains elements of both eurnated and mature types in its midst. 

Behavior: 
Osteomas are very slow growing and are mostly asymptomatic.  They always stay benign and don't recur after excision.

Common sites:

95% osteomas in the sinonasal region arise from the frontoethmoidal region.

80% of osteomas in the sinus region arise from the floor of frontal sinus.  When dealing with frontal sinus osteoma it could be useful to determine whether it lies medial
or lateral to the plane of lamina papyracea.  This distinction is useful in determining the feasibility of endoscopic excision.  Lateral tumors usually needs external approach
for complete removal.

Symptoms:

1. Mass effect causing head ache

2. Diplopia

3. Facial deformity

4. Sinusitis

5. Dizziness

6. Chronic rhinosinusitis

7. Mucocele formation

Radiology:

Plain sinus radiographs are adequate for detecting osteomas of paranasal sinuses.  CT scans are more sensitive in demonstrating even small ones.

In plain radiographs osteomas appear are dense,  homogenous, well circumscribed masses attached with a narrow pedicle / broad base.

To rule out intracranial extension MRI scan could be of help.

Extrasinus complications:

1. Orbital complications - diplopia, epiphora, facial distortion and blindness.  Removal of osteomas usually may bring back normal vision.

2. Intracranial complications - Involvement of dura, mucoceles, meningitis, CSF leak, pneumatocele.

Management:

Small osteomas need not be treated.

Larger ones must be surgically removed.

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