Keywords
osteoblastoma - temporal bone - lateral skull base - retrosigmoid - retrolabyrinthine
Introduction
Osteoblastomas are rare bone tumors, accounting for approximately 1% of all primary
bone neoplasms. These tumors typically arise in the spine and show a 3:1 male predominance.[1] Lesions involving the temporal bone are extremely rare, with 22 total cases reported
in the English-language literature and only 8 cases reported in otolaryngology over
the past 20 years.[2] Of the reported cases, complete resection of tumor has only been attempted a handful
of times, and a combined retrosigmoid, retrolabyrinthine approach has not previously
been described to our knowledge.
Observation
An otherwise healthy 15-year-old boy presented for evaluation of right-sided postauricular
pain. The pain was localized, and there were no associated hypoacusis, tinnitus, otorrhea,
dizziness, or focal neurologic deficits. The patient was tender behind the right ear,
with boggy edema of the skin overlying the bone. An audiogram was normal.
Initially, the patient's primary care physician prescribed pain medications for management;
however, due to persistence of symptoms, imaging was ultimately obtained. The patient
underwent a contrast-enhanced computed tomography (CT) scan ([Fig. 1a]), which showed a heterogeneous, enhancing 4-cm mass lesion abutting the posterior
aspect of the right temporal bone. The lesion was expansile, thinning overlying posterior
fossa calvarium and invading the posterior aspect of the mastoid air cells. Many small
internal calcifications were also noted. Subsequent CT angiography of the head ([Fig. 1b, c]) demonstrated that the right transverse sinus was severely tapered to its transverse/sigmoid
junction.
Fig. 1 (a) Axial contrast-enhanced computed tomography (CT) and (b) coronal computed tomography
angiography (CTA) images show a large heterogeneous mass along the posterior aspect
of the right temporal bone with dense calcifications. (c) Sagittal CTA image shows
that the transverse sinus tapers to a point (arrow) at the superior margin of the
lesion with no definite continuation.
Magnetic resonance imaging (MRI)/magnetic resonance venography (MRV) of the head showed
that the majority of the mass avidly enhanced with several small internal foci that
did not ([Fig. 2a, b]). The lesion appeared to be well encapsulated and completely extradural. There was
no evidence on any imaging modality to suggest that the lesion had intradural involvement.
The lesion had no T2 signal within it ([Fig. 2c]), and it also demonstrated a large amount of dark signal on the gradient images
([Fig. 2d]); this indicated a relative lack of water and a large amount of calcification within
the lesion, respectively. MRV also showed severe tapering and probable occlusion at
the right transverse/sigmoid sinus junction. Differential diagnosis at this time included
benign bone processes, such as osteoid osteomas, aneurysmal bone cysts, or fibrous
dysplasia, and malignant processes, such as osteogenic sarcomas, chondrosarcoma, or
metastatic disease. Even with extensive imaging, a diagnosis was not achieved. Though
the heterogeneous nature of the mass directed our decision making toward a bony process.
The extradural nature of the mass made surgical en bloc resection an appropriate treatment
option.
Fig. 2 (a) Axial T1 precontrast and (b) T1 postcontrast magnetic resonance imaging (MRI)
images show a T1 dark mass lesion, which avidly enhances. (c) Axial T2 MRI shows that
the lesion is significantly dark, indicating the relative lack of water content in
the mass, whereas (d) axial gradient MRI shows extensive dark signal related to the
calcification.
Thus, due to the large size of the tumor, the patient's age, and the fact that the
differential diagnosis included malignancy, surgical management was offered for both
diagnostic and curative purposes. The patient underwent a combined retrolabyrinthine/retrosigmoid
dissection via a right transtemporal approach. Neuronavigation (BrainLab; Westchester,
Illinois, USA) and neuromonitoring (cranial nerves V and VII as well as somatosensory
evoked potentials [SSEPs] and cortical evoked potentials) were utilized intraoperatively.
Initially, a limited retrosigmoid craniotomy was performed to allow posterior exposure
of the tumor and control of the transverse sinus. This was followed by a mastoidectomy
to allow for full exposure of the tumor mass that involved a significant portion of
the posterior temporal bone. The mass extended from the tegmen all the way into the
retrofacial air cell system, as well as a significant portion of the posterior petrous
bone from tegmen to retrofacial air cells. Important landmarks were identified, including
the tegmen, the region of the sinodural angle, and the ear canal, incus, horizontal
semicircular canal, and the vertical segment of the facial nerve. The bone surrounding
these structures was noted to be soft, doughy, and highly vascularized. Biopsies were
taken and sent for frozen section and permanent section analysis. Intraoperative pathology
revealed a bone-forming neoplasm with immature bone as well as spindle cell populations
with rich vascularity ([Fig. 3]). The pathology team read the sample as a “benign tumor, otherwise unspecified.”
There were no malignant features noted such as increased nuclear to cytoplasmic ratio
or extensive mitotic figures to suggest a malignant process. At this point it was
felt that a total en bloc resection would be curative, and the surgeons proceeded
with the operation.
Fig. 3 Hematoxylin and eosin (H&E) stained slide at 200× magnification shows a bone-forming
neoplasm with immature bone (arrow) and spindle cell population with rich vasculature.
Large diamond burrs were used to progressively remove the tumor mass down to normal
dura and normal surrounding bone. On initial inspection, the otic capsule appeared
to be spared. Following the retrolabyrinthine dissection, a Spetzler curette was used
to completely elevate the tumor off normal-appearing, intact dura in the middle fossa.
The facial nerve was then fully delineated and preserved, from external genu to the
stylomastoid foramen. The bone surrounding the facial nerve and the retrofacial system
was relatively normal and therefore felt to be free of tumor burden.
The only area of questions as to the integrity of the otic capsule was at the posterior
semicircular canal. The operculum was identified, as was the transition from the endolymphatic
sac to the endolymphatic duct. At the endolymphatic duct, the bone remained quite
soft until the otic capsule, which appeared to be more resistant to bone destruction,
and thus it was felt that this portion was free of tumor burden.
At this point, there appeared to be normal, intact dura in the middle fossa, the sinodural
angle region, and down onto the sigmoid sinus. There was some initial bleeding from
the sigmoid sinus that was easily controlled using Gelfoam (Pfizer, New York, New
York, USA) and Surgicel (Ethicon, Somerville, New Jersey, USA). The wound was adequately
irrigated and it was felt that gross resection of the tumor was achieved. The aditus
ad antrum was closed off with a large piece of thin, implantable AlloDerm (LifeCell,
Bridgewater, New Jersey, USA) to prevent a potential cerebrospinal fluid (CSF) leak,
though the tumor was entirely extradural and there was no leak noted intraoperatively.
Next, large pieces of Gelfoam were placed in the bony defect and a cranioplasty was
performed using the patient's native retrosigmoid craniotomy bone flap, secured with
an OsteoMed (Addison, Texas, USA) titanium cranioplasty plate. The drilled out mass
was then packed with Gelfoam and a piece of titanium mesh was placed over the mastoid
to recontour the normal surface area of the bone. Next, the muscle and galea were
reapproximated together and the deep dermal layer was reapproximated with 3–0 Vicryl
suture. The dermis was then reapproximated with an external continuous locking stitch
using 3–0 nylon suture. A compression ear dressing was placed, and the patient was
returned to anesthesiology for extubation and transport to recovery.
Pathologic analysis of permanent specimens identified osteoblastoma, a benign, bone-forming
tumor ([Fig. 3]). To date, this patient has had 12 months of follow-up with no evidence of tumor
recurrence. Postoperative temporal bone CT ([Fig. 4a]) and MRI scans are shown ([Fig. 4b]). Postoperative MRV again demonstrates probable occlusion of the right sigmoid sinus
([Fig. 4c]). The patient has no cranial nerve deficits, headaches/postauricular pain have resolved,
and hearing is normal. Evaluation by the medical oncology team found no need for adjuvant
therapies such as radiation or chemotherapy.
Fig. 4 (a) Immediate postoperative axial noncontrast computed tomography (CT) image shows
the large postoperative skull defect with graft and air. No residual tumor was seen
on CT or magnetic resonance imaging (MRI). (b) Postoperative T2 bright fluid in the
resection site. No evidence of residual tumor postoperatively. Note overlying mesh
lateral to the operative site (arrow). Coronal and axial magnetic resonance venography
(MRV) images show narrowing but patency of the right sigmoid sinus, which severely
tapers just before the jugular bulb. (c) The jugular bulb was widely patent.
Discussion
Osteoblastomas were described, almost concurrently, by Lichenstein and Jaffe in 1956.[3]
[4] They are rare, histologically benign, vascular, osteoid-forming neoplasms that account
for only 1% of primary bone tumors.[5]
[6] The most frequents sites of involvement are the posterior elements of the vertebrae
and metaphyses of long bones; however, up to 15% arise within the bones of the craniofacial
skeleton.[7] The most common site of involvement in this anatomic location is the maxilla, but
other areas, notably the temporal bone, do occur ([Table 1]).
Table 1
Twenty-two Reported Cases of Osteoblastomas Located in the Temporal Bone
|
Author
|
Year
|
Age
|
Sex
|
Symptoms
|
Location
|
Intervention
|
Length of F/U
|
Outcome
|
|
Lichtenstein[3]
|
1956
|
9 y
|
F
|
Not described
|
Rt; S
|
PR
|
13 mo
|
NR
|
|
Lichtenstein and Sawyer[13]
|
1964
|
78 y
|
M
|
HA
|
U/K
|
PR
|
4 y
|
NR
|
|
Ronis et al[14]
|
1974
|
13 y
|
M
|
HL, pulsating
|
Rt
|
PR
|
13 mo
|
NR
|
|
Glasscock et al[15]
|
1978
|
57 y
|
F
|
Severe pain
|
Rt
|
TR
|
U/K
|
NR
|
|
Potter et al[16]
|
1983
|
19 y
|
F
|
OM
|
R; M,P,S
|
E, PR
|
18 mo
|
NR
|
|
Naclerio et al[17]
|
1985
|
4 y
|
F
|
FP, HL
|
L; M,P
|
TR
|
12 mo
|
NR
|
|
Gellad et al[18]
|
1985
|
30 y
|
F
|
T; puffiness; HL
|
R; M
|
PR
|
7 y
|
R
|
|
Miyazaki et al[19]
|
1987
|
7 m
|
F
|
Swelling
|
L; S
|
TR
|
19 mo
|
NR
|
|
Matsumoto et al[20]
|
1989
|
29 y
|
M
|
HA
|
R; M,P,S
|
TR
|
9 mo
|
NR
|
|
Adler et al[1]
|
1990
|
28 y
|
F
|
Pain; FP
|
R; M,P,S
|
PR + rad
|
5 y
|
R
|
|
Singer and Deutsch[21]
|
1993
|
16 y
|
M
|
Pain
|
L; M,P
|
PR + rad
|
10 y
|
R
|
|
Khashaba et al[22]
|
1995
|
16 y
|
F
|
Pain; FP
|
L; M
|
TR
|
none
|
U/K
|
|
Tsuchida and Nagao[23]
|
1995
|
27 y
|
F
|
Pain
|
R; S,P
|
TR
|
U/K
|
U/K
|
|
Ohkawa et al[24]
|
1997
|
28 y
|
F
|
Pain
|
L; S,P
|
E, TR
|
3 y
|
NR
|
|
Figueiredo et al[25]
|
1998
|
23 y
|
M
|
HL, swelling and pain
|
L; M,P,S
|
E, TR
|
18 mo
|
NR
|
|
Low et al[26]
|
2000
|
8 y
|
F
|
Swelling
|
L; S
|
TR
|
13 mo
|
NR
|
|
Doshi et al[27]
|
2001
|
19 y
|
F
|
T, HL
|
R; M,P
|
PR
|
15 mo
|
NR
|
|
Ugur et al[28]
|
2005
|
45 y
|
F
|
Diplopia and HA
|
R; P
|
PR
|
18 y
|
NR
|
|
Shimizu et al[5]
|
2006
|
61 y
|
F
|
HL
|
L; M,P,S
|
E, PR
|
24 mo
|
NR
|
|
Tugcu et al[29]
|
2008
|
23 y
|
M
|
Swelling and tenderness
|
R
|
U/K
|
U/K
|
U/K
|
|
Pérez-Mora et al[9]
|
2009
|
26 y
|
F
|
T, HL
|
R; M
|
TR
|
10 mo
|
NR
|
|
Njim et al[2]
|
2010
|
22 y
|
F
|
Pain, swelling
|
L; M
|
TR
|
1 y
|
NR
|
|
Present case
|
2012
|
15 y
|
M
|
Swelling, tenderness
|
R; M,P,S
|
TR
|
8 mo
|
NR
|
Abbreviations: E, embolization; FP, facial palsy; HA, headache; HL, hearing loss;
M, mastoid portion; NR, no recurrence; OM, otitis media; P, petrous portion; PR, partial
removal; R, recurrence; rad, radiation; Rt, right; S, squamous portion; T, tinnitus;
TR, total removal; U/K, unknown/not described.
These tumors occur predominantly in young men, with a 3:1 predominance over females.
They are usually diagnosed in the second through fourth decades of life. Tumors express
high levels of osteoblastic lineage regulatory genes such as Osterix and Runx2. Overexpression of these genes in transgenic mice results in defective osteoblastic
maturation with generalized immature bone and an osteopenic phenotype.[8] Clinically, symptoms are usually nonspecific and include localized, insidious pain
that is unresponsive to anti-inflammatory agents.[9] There may also be soft tissue swelling and erythema over the area of tumor growth.
When the tumor affects the temporal bone and middle ear structures, it can lead to
progressive hearing loss (typically conductive) and facial nerve palsy due to compression.[9]
Twenty-two temporal bone osteoblastomas have been described in the literature previously.
These patients were treated with either partial resection or total resection. Only
3 of the 22 patients showed recurrence of the tumor. Notably, these three patients
only underwent partial tumor removal, and recurrence was likely due to tumor bulk
remaining postoperatively.
The radiographic appearance of osteoblastomas is variable and often nonspecific.[7] On imaging, aggressive osteoblastomas can mimic other tumors, including malignant
varieties. The differential diagnosis in such instances consists of osteoid osteomas,
aneurysmal bone cysts, osteogenic sarcomas, fibrous dysplasia, chondrosarcoma, and
metastatic disease. Osteoblastomas typically demonstrate intratumoral ossification,
including some with a central nidus of sclerotic bone encompassed by a radiolucent
halo similar to osteoid osteoma.[7] Most osteoblastomas remain confined to bone and do not destroy or penetrate cortex;
however, up to 12% have features that mimic a malignant process.[10]
Histologically, osteoblastomas display a predominance of immature bone with high levels
of osteoblastic activity. Many are composed of interanastomosing trabeculae of woven
bone set within large spindle cell populations with rich vascularity.[7]
Current literature regarding osteoblastoma of the spine suggests that en bloc resection
is sufficient as definitive treatment for these tumors. Radiotherapy does not alter
the course of the disease and may be contraindicated for fear of malignant degeneration.[11] We are unaware of any English-language studies specifically evaluating the role
of radiation therapy for osteoblastomas of the temporal bone or skull. Additionally,
current literature finds no role for chemotherapy in primary, singular, benign bone
tumors.[12] Accordingly, after en bloc resection of the tumor, our patient did not undergo any
further therapy.
In summary, osteoblastomas are benign bone-forming tumors that rarely involve the
craniofacial skeleton. The majority of these neoplasms occur in the spine and long
bones. En bloc resection is sufficient and curative, with no adjuvant chemotherapy
or radiation necessary.
