AJR 2003; 181:891
© American Roentgen Ray Society
Extensive Occipital Bone Pneumatization Presenting as an Occipital Mass
Steven Pans,
Iwan Van Breuseghem,
Eric Geusens and
Peter Brys
University Hospitals Gasthuisberg Leuven B-3000, Belgium
A 52-year-old man was referred to the radiology department for evaluation
of a palpable mass that had spontaneously developed in the midoccipital
region. The patient reported that pressure of the mass caused tinnitus and
dizziness and that he had a minor hearing loss, which was confirmed with
audiometry.
Sonography revealed a 33-mm cystic subcutaneous structure. Conventional
radiographs of the skull and cervical spine showed extensive lucent areas in
the occiput and atlas (Fig.
4A). Posterior relative to the occipital bone, subcutaneous free
air was identified that corresponded to the mass revealed on sonography. CT
scans of the skull, skull base, and upper cervical spine showed no
intracranial anomalies. However, the extensive pneumatization of the skull
base and C1 vertebra and the presence of subcutaneous free air posterior
relative to the occipital bone were confirmed. The outer cortex of the occiput
was fractured, causing a connection between the free air and the occipital
bone (Fig. 4B). Reformatted
coronal CT scans confirmed the extent of the pneumatization
(Fig. 4C) and clearly showed an
associated atloidooccipital assimilation. The patient underwent a surgical
placement of a tympanic tube in his right ear. A CT scan obtained 3 weeks
later showed a slight decrease of the subcutaneous air collection.
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Fig. 4A. —52-year-old man referred for evaluation of palpable mass that
had spontaneously developed in midoccipital region. Lateral radiograph of
skull base shows extensive radiolucent areas in occiput and atlas, with
subcutaneous free air (arrow) posterior relative to occipital
bone.
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Fig. 4B. —52-year-old man referred for evaluation of palpable mass that
had spontaneously developed in midoccipital region. Axial high-resolution CT
scan obtained with bone window setting through occipital bone reveals
extensive pneumatization of occiput and posteriorly located collection of free
air. Outer cortex of occiput is fractured, causing connection between free air
and occipital bone.
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Fig. 4C. —52-year-old man referred for evaluation of palpable mass that
had spontaneously developed in midoccipital region. Coronal reformatted CT
scan obtained with bone window setting through atloidooccipital region shows
extensive pneumatization (arrow) of atlas and atloidooccipital
assimilation.
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Temporal bone pneumatization is considered a normal variant in adults. The
condition can affect the mastoid, squamomastoid, perilabyrinthine, and petrous
apex portions of the temporal bone and is seen in varying degrees of severity
in healthy individuals [1].
However, pneumatization of the occipital bone is rare and has been only
sparsely reported. In one case described in the literature, occipital bone
pneumatization was an incidental finding on a CT scan obtained to evaluate the
cause of the patient's headaches
[2]. Another report described a
patient whose findings were similar to those of our
patient—pneumatization of both the occiput and the atlas—but the
pneumatization in that patient was thought to have resulted from trauma
[3]. In our patient, it was
assumed to have developed spontaneously. Atloidooccipital assimilation due to
a developmental abnormality [4]
could explain pneumatization of the atlas by extension from the temporal and
occipital bones that we found in our patient
(Fig. 4C).
To our knowledge, ours is the first reported case of craniocervical
pneumatization associated with a subcutaneous air collection communicating
through a bony defect with the occipital bone. The free connection of the
subcutaneous air with the middle ear, as revealed on the CT scan, might
explain the symptoms experienced by our patient. We find it noteworthy that
extratemporal pneumatization could cause the appearance of a radiolucent skull
base. CT findings are diagnostic and can reveal the extent of this type of
pneumatization.
References
- Virapongse C, Sarwar M, Bhimani S, Sasaki C, Shapiro R. Computed
tomography of temporal bone pneumatization. 1 Normal pattern and morphology.
AJR 1985;145:473
-481[Abstract/Free Full Text]
- Sener RN. Air sinus in occipital bone. (letter)
AJR 1992;159:905[Medline]
- Lo WWM, Zapata E. Pneumatization of the occipital bone as a cause
of radiolucent skull lesion. AJNR1983; 4:1249
-1250[Medline]
- Smoker WR. Craniocervical junction: normal anatomy, craniometry and
congenital anomalies. RadioGraphics1994; 14:255
-277[Abstract]
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