2.2 Management strategies
This study series was divided into 3 groups based on management
strategies, namely, the observation group, the surgery group, and the
optic nerve decompression group.
The observation group included 9 patients with
asymptomatic MFD, and adopted the
method of clinical observation and regular fellow-up. The patients
received a paranasal sinus CT scan periodically. The clinical data were
shown in Table 1. Three of the nine patients had chronic rhinosinusitis,
who received functional endoscopic sinus surgery (FESS) only for their
chronic rhinosinusitis. The other six patients were found with FD on
physical examination. Two of them received a biopsy through an
endoscopic endonasal approach.
The surgery group included 10 patients with symptomatic MFD.
The clinical data were shown in
Table 2. Five of the patients underwent FESS for their chronic
rhinosinusitis simultaneously. FD was relatively hard and was removed by
an electric drill (Medtronic IPC, USA)and Kerrison Rongeurs. Seven of
the cases were excised with the aid of image-guided navigation (Fusion,
Medtronic ENT, USA) (Fig. 3C, 3D).
The optic nerve decompression group included 4 patients with vision
loss, who underwent endonasal endoscopic optic nerve decompression with
the aid of image-guided navigation. The clinical data were shown in
Table 3. One of the patients received bilateral endoscopic optic nerve
decompression simultaneously. The MAS patient accepted the first surgery
of left endoscopic optic nerve decompression in February 2016 and again
in July 2017 (Fig. 3A and 3B).
Result
The patients in the observation group were followed up regularly. For
example, in case one in table 1 the
paranasal sinus CT scan in June
2008 showed ivory high-density pattern sphenoid bone FD, then the
patient received endonasal endoscopic biopsy and was diagnosed as FD by
histopathological examination. He was asymptomatic and followed up
regularly. The paranasal sinus CT taken in 2008 was compared with the
paranasal sinus CT reviewed in 2016, which revealed that the FD was in a
static state (Fig.1).
In the surgery group, five patients with ethmoid bone FD underwent total
resection, while three patients with sphenoid bone FD underwent subtotal
resection and two patients underwent partial resection through an
endonasal endoscopic approach. Five of the patients underwent FESS for
their chronic rhinosinusitis simultaneously. The symptoms of the
patients were relieved after surgery, and there were no intracranial or
intraorbital complications. The patients in this group were followed up
for 1-13 years, and there was no recurrence.
During the operation, we found that although some
MFD lesions were large, neither the
germinal center nor the pedicle was large.
A thin layer of fibrous tissue
separated FD from normal bone, and
it was relatively safe to dissect along this layer of fibrous tissue.
For example, case three in Table 2 is a two-year-old boy. The patients’
paranasal sinuses CT scan showed that the left ethmoid sinus and nasal
cavity were filled with a large (40.5mm×6.3mm×29.9mm) and highly dense
mass (Fig. 2). The mass originated from the left cribriform plate,
compressed the left lamina papyracea, and extended to the bottom of the
nasal cavity. The frontal sinuses and sphenoid sinuses were undeveloped.
The thin
layer
of fibrous tissue was found between the FD and the partial cribriform
plate and lamina papyracea during the surgery (Fig. 2). This phenomenon
was also seen in the resection of sphenoid bone FD (Fig. 3C).
In addition, MFD may have degenerative changes with age, as shown in
case 4 and case 5 (Fig. 3D) in table 2. The paranasal sinus CT of case 5
revealed frosted glass changes of the left sphenoid pterygoid process
and great wing, with a 2.3× 1.0 cm soft tissue shadow. The
pterygoid process and great wing change was diagnosed as FD and the
‘soft tissue shadow’ change was determined to be hyaline degeneration by
pathological examination.
In the optic nerve decompression group, the effects of optic nerve
decompression were shown in Table 3. The youngest patient in this group,
a 10-year-old girl with MAS, showed left visual loss again one and half
a years after her first left optic nerve decompression. The patient
received left optic nerve decompression again, and the left visual
acuity remained stable so far. However, the CT showed that the right
optic nerve was encased by FD, but the patient’s right eye vision
remained stable all the time (Fig.3A and 3B). Case 1 in Table 3
underwent bilateral optic nerve decompression due to cystic degeneration
from FD (Fig. 3E). The CT scan of 2 years before surgery revealed that
the left optic nerve was completely encased and the right optic nerve
was partially encased by FD (Fig. 3F, G, H), but the vision was normal
until 1 month before the surgery.
Discussion
In view of the rarity, complex and varied natural history, and clinical
manifestation of FD, it is difficult for clinicians to develop a
standardized treatment plan. As a consequence, no treatment guidelines
currently exist 1. Although there was not an
international guideline for the management of FD/MAS, an international
workshop has been set up to focus on improving FD/MAS management and
understanding the importance of a multidisciplinary team for the
lifetime management of FD/MAS 7.
FD treatment includes clinical observation, medical therapy and surgery.
Medical treatment for FD is limited to relieving a patient’s symptoms.
One of these medications is bisphosphonate, which may help to improve
the function, relieve the pain, and reduce the fracture risk. However, a
recent randomized, double blind, placebo-controlled trial disputed these
effects 8,9. Radiotherapy is contraindicated owing to
high prevalence of malignant transformation. Therefore, clinical
observation and surgery are currently the main treatment strategies for
FD.
Clinical observation is adopted for asymptomatic FD patients, but the
patients should be required to have periodic radiologic evaluations. As
FD is a slow-growing lesion, tends to be stable after puberty, and has a
low malignancy potential, most of the specialists recommend clinical
observation if there are no symptoms, but periodic imaging should be
performed to confirm that there is no progression or regrowth in
follow-up 1. Comparing craniofacial FD management
between 1980 and 2002 with management between 2003 and 2013 showed that
observation has replaced surgery as the most used method. Watching
carefully and attentively was indicated in cases of stable lesions, and
it was the best therapeutic option, if possible 4. In
France, with the establishment of National Reference Centers, 57
specific recommendations have been provided for the diagnosis,
prognosis, and follow-up of patients with FD/MAS. If the skull and/or
facial bones are involved, a skull CT is recommended to accurately
evaluate the risk of neurological compromise due to alterations of the
foramina. MRI should be viewed as a second-line imaging study.
Radiographic monitoring is recommended every 2-3 years for follow-up
patients 10. It was demonstrated that the
characteristics of FD on CT and the natural radiographic progression may
vary from a “ground-glass” or homogenous appearance to a mixed
radio-dense/radio-lucent lesion as the patient ages 2.
Based on preoperative radiology, the sensitivity and specificity to
correctly detect FD were 54.6% and 96.9%, respectively.
Lesions with classic ground glass appearance or mixed pattern on CT
should not warrant diagnostic biopsy, especially in asymptomatic
patients. However, if radiologic diagnosis is uncertain, biopsy may be
warranted to arrive at the definitive diagnosis based on radiographic
and histologic correlation 11. Biopsy of a lesion does
not specifically induce growth of FD, but if the lesion is asymptomatic,
and/or in the cranial base, a biopsy may not be necessary2.
Surgery is indicated in symptomatic patients. Although application of
surgical treatment for craniofacial FD is controversial, many
publications have provided views on the surgical treatment of FD12-14. Comparing craniofacial FD management between
1980 and 2002 with management between 2003 and 2013 revealed that
radical resection (if possible) of FD was the only technique to obtain
resolution of the disease 4. The advantages of
surgical treatment of FD should be appropriately weighed against
possible complications 1. The aim of the surgical
treatment for craniofacial FD is to remove the bulk of the lesion,
reserve the cranial nerve compression, and resolve the aesthetic problem6. The extent of the resection should be based on the
location of the pathological bone and its proximity to important
structures, as radical or complete resection may not be necessary or
possible 5. Treatment protocols should be tailored to
individual patient’s needs, with the aim to achieve the best possible
esthetic and functional outcome with the least postoperative morbidity15-16. Therefore, surgical treatment planning must
take into account several factors (i.e., natural history of the disease,
presence of symptoms, site of the lesion, and the relationship with
critical anatomic structures) 1.
Early surgery is necessary for the patient with MFD when the lesion was
limited to ethmoid or sphenoid bone with obvious symptoms. It is because
the growth and expansion of the FD may lead to the obstruction of the
sinus ostia and result in rhinosinusitis and mucocele. Furthermore, it
has been reported that the lesion may oppress the adjacent bone, such as
the lamina papyracea and the anterior skull base, extend into the orbit
and intracranial cavity, and ultimately lead to epiphora, diplopia,
proptosis, impairment of visual acuity, meningitis, cerebrospinal fluid
leak, and so on 17. Five patients with ethmoid bone FD
and three with sphenoid bone FD in the surgery group of this study
series underwent total resection or subtotal resection through an
endonasal endoscopic approach respectively. Only two patients with
sphenoid bone FD underwent partial resection through an endonasal
endoscopic approach. And five surgery group patients underwent FESS for
their chronic rhinosinusitis simultaneously. Meanwhile, what we found in
these procedures was that in the process of FD expansion toward the
cavity of a paranasal sinus, the epithelial tissue in the sinus cavity
may be compressed into a thin layer of fibrous tissue, which separated
FD from normal bone, and it was relatively safe to dissect along this
layer of fibrous tissue. Combined with use of intraoperative
image-guided navigation and advanced surgical instruments, these
surgeries were performed successfully without intracranial or
intraorbital complications.
For FD patients with impaired vision, it was recommended to have optic
nerve decompression as soon as possible. However, if FD was encroaching
on the optic nerve without impaired vision, prophylactic decompression
is not recommended. This is the current consensus1,18-20. A retrospective analysis in 91 patients with
craniofacial FD involving the optic nerves showed that 17% of nerves
were less than 50% encased, 22% were 50-99% encased, and 61% were
100% encased. Yet optic nerve decompressions were performed in only 13
patients (6 prophylactic and 7 therapeutic) since the authors regarded
that the majority of optic nerves encased with FD did not present
symptoms of optic neuropathy and appeared to be stable over time18. Satoh K, et al. held that current strategies
should focus on esthetic improvement, with careful observation carried
out to assess for optic canal
encroachment without prophylactic decompression 19. In
another study, in asymptomatic patients, stable vision occurred in 76%
of patients receiving decompression and 95% of patients not undergoing
surgery (P< 0.001). Vision impairment may be associated
with the concomitant presence of cystic lesions (i.e., mucocele,
hemorrhage, and aneurysmal bone cyst) 20. Holl DC, et
al. reported a case of FD in which the patient developed an aneurysmal
bone cyst leading to left optic nerve compression with an acute visual
loss. An emergency optic nerve decompression resulted in complete
restoration of vision. 21. In this study, one patient
had acute bilateral visual loss due to cystic degeneration formation.
Another patient with MAS underwent left optic nerve decompression twice,
but in fact, although the CT showed that the right optic nerve was
encased by FD, the right eye vision of the patient remained stable all
the time.
Navigation plays an important role in paranasal sinus and adjacent skull
base FD resection, and in optic nerve decompression. Stereotactic
navigation was recommended, as the FD/MAS process often distorted normal
intranasal landmarks used in sinus surgery 5.
Navigation assisted, endonasal endoscopic optic nerve decompression was
usually effective for the treatment of nontraumatic optic neuropathy22.
Conclusion
Clinical observation is adopted for asymptomatic patients with FD, but
the patients should be required to undergo periodic radiologic
evaluations. Surgery is indicated in symptomatic patients. In FD
patients with visual change or vision loss, an optic nerve decompression
was recommended as soon as possible; however, if FD is encroaching on
the optic nerve without impaired vision, prophylactic decompression is
not recommended. Navigation plays an important role in paranasal sinus
and adjacent skull base FD resection and optic nerve decompression.