State Of The Art in Temporal Bone Malignancies

Radio-clinical assesment & review

presented by Tamer S. Ebaied

Ass.Lecturer ENT Department Alexandria University

Introduction

Temporal bone malignancies (TBMs) refer to a rare but distinct set of neoplasms originating within the confines of the temporal bone that account for approximately 0.2% of all head and neck malignancies.

The annual incidence of such tumors is estimated to be between 1 and 6 per million population. The incidence of TBMs at the Gruppo Otologico(Piacenza-Rome), which is a quaternary referral center for diseases of the skull base, is 130 (0.5%) cases for about 25 000 otological inpatient admissions over three decades.

The rarity of these tumors can be adjudged by the fact that, in the last 15 years, there have been just about 20 series published dealing with squamous cell carcinomas (SCCs) of the temporal bone with a study population of over 20 patients, the largest series being that of Yin et al.

Nonsquamous TBMs are even more rarely reported, most of them being limited to case reports.

Squamous carcinoma is the most frequent neoplasm in the external auditory canal(EAC), about four times more common than basal carcinomas. This ratio is reversed in the pinna.

These tumors have been associated with chronic suppurative otitis media and exposure to chemicals, though the most important factor may be previous radiotherapy.

Most squamous cell carcinomas (SCC) of the temporal bone occur in the fifth and sixth decades of life.

Otorrhea is the primary symptom, and otalgia, hearing loss, and bleeding may be frequent as well.

Diagnosis is usually delayed because symptoms are quite similar to other benign otologic conditions such as chronic suppurative otitis media.

The extent of disease, positive margins, Dural involvement, facial nerve paralysis, cranial nerve involvement, or moderate to severe pain on presentation have been associated with poorer outcomes.

Ear pain and discharge may initially be mistaken for external otitis . Late diagnosis is common and worsens prognosis.

In the presence of non-specific clinical features and doubtful otoscopic findings (especially invasive forms),biopsy must be performed, preferably in the operating room to ensure good quality biopsy samples for histological examination.

Why it is difficult to study :

* Because of the rarity of these tumors, it has been difficult for a single institution to analyze the data and formulate an optimal evaluation and treatment strategy.

* Another impediment to the study of TBMs is the lack of a universally accepted staging system. There is no recognized American Joint Committee on Cancer or International Union against Cancer staging system .

* The T staging that is currently available and still in the process of evolution, was adopted from a series of articles that were published by the Pittsburgh University for SCC of the external auditory canal (EAC).

A literature review indicates that unlike SCC of the EAC, there has been no serious attempt to classify and stage TBMs of other histologies and sites of origin other than the EAC.

Improvement in management of TBM:

However, over the years, morbidity and mortality in temporal bone resections have reduced significantly because of advances in neuroimaging and skull base surgery . Moreover, the otologist/skull base surgeon of today is more compliant with the general oncological principles and practices than a few decades earlier.

From very poor prognosis a few decades ago, using a combination of surgery and adjuvant radiotherapy, up to 100% 5-year survival rates have been achieved by many authors for T1 and T2 tumors and up to 86 and 48% respectively in T3 and T4 tumors, which indicates the progress made globally in the control of this disease.

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Origin And Spread Of Temporal Bone Malignancies :

The temporal bone is host to both primitive and metastatic neoplasms.

Most of the ‘primitive’ neoplasms affecting the temporal bone are epithelial neoplasms arising from the middle and inner ear including SCCs , endolymphatic sac tumor and adenoid cystic carcinomas.

Secondary tumors may take origin as a direct extension from auricle, central nervous system, pharynx or salivary glands or even by blood-borne distant metastases.

Sites of origin of TBM:

TBMs have been reported to arise from practically all parts of the temporal bone including the EAC, middle ear, mastoid, endolymphatic sac, petrous apex and the internal auditory canal (IAC),as the following table:

Local Spread Of TBM :

TBMs can be locally aggressive due to the presence of numerous pathways in the temporal bone along which the tumor can spread from the site of origin.

Instead of creating a barrier to the tumor’s diffusion, the temporal bone in fact acts as a medium for microscopic diffusion through bony canals and interosseous vessels and nerves.

The petrosquamous suture line, the fissures of Santorini, the foramen of Huschke, the stylomastoid foramen, the round and oval windows, the mastoid air cells system and the tympanic membrane all provide pathways for tumor spread.

Also, The bone plates over many structures like the jugular bulb, carotid, tegmen, fallopian canal and the labyrinth are thin and are hence vulnerable to tumor erosion.

Histopathological variants in TBM

Tumors of the temporal bone can arise From any component either epithelial or non as shown In the following table:

Staging of temporal bone malignancies Staging of TBMs is important for determining prognosis and outcome after treatment. However, standardized staging system has not yet been accepted internationally .

In 1980, Goodwin and Jesse divided SCC of the temporal bone into three sites based on their origin: concha and cartilaginous meatus, osseous meatus, and middle ear. This is valid as malignancies arising from each of these sub sites have different tumor behavior and it would be unwise to compare them using the same parameters.

For instance, tumors arising from: *The concha and the cartilaginous meatus tend to invade : the soft tissues earlier than bone and behave more like cutaneous malignancies in other parts of the body. *The tumors involving the osseous meatus tend to involve : the bone anteriorly and posteriorly because of the thin skin.

*The tumors arising from the middle ear may involve the deeper parts of the temporal bone sparing the EAC.

The modified Pittsburgh classification Over the years, many classifications have been proposed , but only the modified Pittsburgh classification for T staging for SCCs of the EAC has gained acceptance. There is still no consensus among authors for tumor staging in other parts of the temporal bone.

N.B: This system fulfills the requirements ofthe American Joint Committee on Cancer that a staging system should provide a sound basis for therapeutic planning for cancer patients by describing the survival and resultant treatment of different patient groups in comparable form.

Correlation between radiological signs and staging:

That TNM staging based exclusively on CT was accurate in 90% of cases for local extension, while parotid gland invasion was only demonstrated by MRI in 10% of cases. In 40% of cases,MRI raised the suspicion of invasion of the temporal dura mater allowing planned dura mater resection.

Although MRI findings have little impact on the TNM staging based on CT, it can be used to evaluate parotid, soft tissue, infratemporal fossa and temporal dura mater involvement . This information is essential for the management of invasive EAC tumors, especially in the case of adenoid cystic carcinoma, for which clinical staging assessment is particularly difficult.

These findings therefore suggest that MRI should be systematically performed for local staging of carcinoma of the EAC.

CONT. An additional strength of the University of Pittsburgh staging system is its ability to stage disease in patients prior to surgery using preoperative CT of the temporal bone. High-resolution CT scans of the temporal bone can readily detect erosion of the bony external canal, which is often the first sign of local spread of disease. Arriaga et al found that interpretation of a preoperative temporal bone CT correlated with surgical histopathological findings in 94 of the 96 anatomic sites compared, for an overall accuracy of 98%. In one case, CT failed to detect the spread of tumor through the anterior canal wall that occurred without bony erosion. In the other case, mucosal inflammation of the middle ear was falsely interpreted as tumor.

Arriaga et al concluded that preoperative high-resolution CT scans of the temporal bone accurately reflect the extent of disease and can therefore be used for preoperative staging and planning for an en bloc resection of the temporal bone.

Cont.

The inability of CT scan findings to predict the anterior soft tissue extent of the tumor has been noted in other studies where Tumor can spread anteriorly via the cartilaginous fissures of Santorini and the bony foramen of Huschke without evidence of bony canal erosion.

In a site-by-site comparison with intraoperative findings, CT and MRI had an overall accuracy of 85%.

Disease was most frequently underestimated in the infratemporal fossa, the mastoid cavity, and the carotid canal.

Correlation between staging and prognosis: histopathological-clinical correlation of the University of Pittsburgh staging system has been supported in recent studies. In a study of 33 patients with squamous cell carcinoma of the temporal bone, Zhang et al found: 5-year survival of 100% in the T1/T2 group 69% survival in patients with T3 tumors 20% survival in the T4 group.

In a similar study, a group of patients with T1 and T2 tumors had 100% survival during the study period (mean follow-up 54 months), whereas there was a 25% and 0% survival rate in patients with T3 and T4 tumors, respectively.

So, The University of Pittsburgh staging system is therefore consistent in its prediction of survival rate among patients with a similar extent of disease.

What are the limitations in That accepted staging system :

Many studies in the past have validated the usefulness of the modified Pittsburgh T staging and reported a good correlation between disease stage and prognosis. However, recent data suggest that such staging is not perfect. Why:

1) According to the classification, facial nerve paralysis as a single factor could upgrade tumors to T4, but Moffat and Wagstaff in their series did not find facial nerve involvement to be a significant prognostic factor. 2) No meaningful comparison can be drawn between different series unless the degree of histopathological differentiation is taken into account. 3) Perineural invasion of the facial nerve did not significantly influence disease-free survival following facial nerve resection.

4) Although extensive (0.5cm) soft tissue involvement was considered as T4 disease in the Pittsburgh staging system, this was not a prognostically significant factor. Zanoletti et al. reported a better prognosis for T4 tumors extending into the anterior soft tissues (parotid and condyle), as opposed to T4 tumors spreading medially, posteriorly and inferiorly.

Cont. to Limitations:

5) Another limitation of the Pittsburgh T-staging system is that it is not possible to apply it for tumors of other subsites of the temporal bone including concha, auricle and periauricular area as tumors in such subsites vary in presentation, extensions, histology and management.

6) It is also uncertain whether the Pittsburgh classification, which was initially proposed for SCC of the EAC, is applicable to other histological types of malignancies arising in the EAC.

Taking into consideration the vast number of tumors that go unstaged,there is presently also a need for a separate staging system for squamous and non squamous malignant tumors of other subsites of the temporal bone.

In view of all these reports, it is clear that the modified Pittsburgh classification needs re-evaluation.

Role of Imaging in TBM:

Imaging is important in TBMs for accurate tumor and node staging as many patients have limited findings on physical examination.

It is now known that the single most important factor determining survival is the local tumor extent at presentation. It is therefore crucial to establish the disease extent in order to optimize treatment option.

So it is important to review the pattern of tumor spread and highlight the value of imaging, particularly magnetic resonance imaging in Pre-operative tumour mapping. High resolution computed tomography of the temporal bone offers the most accurate method for the evaluation of bone erosion due to malignancies. However, a reported limitation of CT is its inability to distinguish between tumor and fluid in the middle ear, soft tissue or mucosal thickening in the absence of bone erosion. Also, spread along fascial planes and neurovascular structures can be difficult to detect.

Radiological features On temporal bone CT, early carcinoma of the EAC commonly presents as a soft tissue mass within the EAC.

As the disease progresses, aggressive underlying bony destructive changes are demonstrated. As the tumour infiltrates and spreads deep into the surrounding tissue, it is best shown as a heterogeneously enhancing lesion on contrast-enhanced MR imaging.

Carcinoma of the EAC most commonly spreads through the floor of the EAC into the soft tissue below the temporal bone. This may be related to the presence of the fissures of Santorini along the inferior aspect of the cartilaginous EAC.

Less frequently, the tumor erodes posteriorly into the mastoid bone or anteriorly through the tympanic portion of the EAC to invade the temporomandibular joint .

Ant.Extention of the tumor :

(a) Axial T1-weighted MR image shows intermediate signal tumor in the left EAC (asterisk) extending into the temporomandibular joint and displacing the mandibular condyle (arrow) anteriorly. (b) Axial contrast-enhanced MR image shows tumor enhancement. Note the tumor extension into the left parotid region (asterisk).

Post. Extension of the tumor:

(a) Axial T1-weighted MR image shows an intermediate signal intensity tumor in the left middle ear cavitywith extension posteriorly into the mastoid (arrow).

(b) Axial contrast-enhanced MR image shows heterogeneous tumor enhancement. Note tumor surrounding the left petrous internal carotid artery (arrow).

Superior extension of the tumor:

(a) Coronal contrast-enhanced MR image shows tumor in the right middle ear (arrow) with extension through the tegmen tympani into the middle cranial fossa. (b) Coronal contrast enhanced MR image (posterior to (a) shows tumor in the right EAC (asterisk) with middle ear and intracranial extension. Note enhancement in the labyrinth (black arrow) and the internal auditory canal (white arrow).

Medial and Inferior Extension of the tumor:

(a) Axial CT shows a right EAC tumor eroding the Otic capsule and destructing the cochlea (asterisk). Notethe normal left cochlea for comparison.

(b) Axial CT shows inferior spread of the right EAC tumor involving the internal carotid artery and jugular bulb (asterisk). Note the normal left carotid foramen (black arrow) and jugular foramen (white arrow) for comparison.

Tumor erosion through the floor of the middle ear anteriorly results in the involvement of the carotidartery while inferior extension through the floor posteriorly involves the jugular foramen .

Cancers with extensive inferior spread involving the jugular bulb and internal carotid artery exclude the surgical options of lateral temporal bone resection and subtotal temporal bone resection, and are often unrespectable.

(a) Coronal CT shows tumor in the right EAC eroding the cochlea (short arrow) and the floor adjacent tothe carotid canal (long arrow). (b) Coronal CT shows permeative erosion of the roof of the right middle ear (short arrow), and the floor adjacent to the jugular foramen (long arrow). (c) Coronal contrast-enhanced MR image shows enhancing tumor in the right EAC spreading into the right middle cranial fossa causing gross Dural thickening (asterisk) (d) Axial contrast-enhanced MR image shows moderate tumor enhancement. The tumor has obliterated the right jugular foramen and vein (asterisk). Note the normal enhancing left jugular vein (arrow) for comparison.

Tumor Extension through the E.T and nasopharyngeal affection:

Tumor in the hypo tympanum often extends anteromedially along the Eustachian tube. This manner of spread can be diagnosed by the identification of soft tissues anterior and parallel to the petrous segment of the internal carotid artery .

When this manner of spread occurs, tumour comes into close proximity with the foramen ovale and the mandibular nerve in the central skull base. Proximal perineural spread along the mandibular nerve leads to intracranial extension.

Tumour extending medially along the Eustachian tube may eventually reach the nasopharynx . The superior portion of the parapharyngeal space is adjacent to the Eustachian tube. The parapharyngeal space is a well-recognized route for the spread of inflammatory and malignant disease.

Tumour may therefore extend into the parapharyngeal space and spread into the neck with relative ease.

Extension to E.T and Nasopharynx:

A 67-year-old male with recurrent carcinoma of left EAC with spread to the nasopharynx. (a) Axial T1-weighted MR image shows an intermediate signal intensity tumour in the left EAC and middle ear extending anteromedially along the Eustachian tube (arrow).

(b) Axial T1-weighted MR image shows tumour in the left parapharyngeal space and nasopharynx (arrowheads).

(e) Coronal T1-weighted MR image shows an intermediate signal intensity tumour in the left nasopharynx (asterisk) extending to the left foramenovale (arrow).

Lymphatic affection by radiological assesment:

Lymph node disease in carcinoma of the EAC is a significant negative prognostic factor. Any malignant nodal involvement should therefore be classified as advanced disease. The parotid nodes are the first echelon nodes. Malignant pre- and post-auricular lymphadenopathy is also commonly seen.

Benefit Of MRI in TBM:

MRI can provide : * excellent differentiation between soft-tissue tumor margin, muscle and soft-tissue infiltration, and can help in distinguishing tumor from obstructive inflammatory changes.

* obstruction of the sigmoid sinus and encasement of the petrous internal carotid artery are better detected on MRI than CT.

* cranial spread into the middle and posterior cranial fossa and caudal spread into the infratemporal fossa, is also better detected on MRI.

* confidently diagnose perineural spread of malignancies. Fat saturation gadolinium-enhanced magnetic resonance(MR) scans are often capable of detecting subtle tumor tracking along the fifth and seventh cranial nerves, as well as other nerves that travel through the many foramina of the skull base, before the lesions have grown sufficiently large to affect the surrounding bone.

But: Despite the advances in imaging, it is still a challenge to exactly determine the size and extensions of TBMs.

In their comparison of preoperative radiographic with intraoperative findings in 26 patients, Leonetti et al. reported that anterior and inferior growth pattern were accurately assessed radiologically, while underestimations of tumor extent were seen with posterior, superior and medial tumor extensions. Another study showed statistical evidence that erosions of less than 2mm on the anterior wall of the EAC are not recognized preoperatively by CT.

also it has been often observed that peritumoral inflammatory changes show amuch larger lesion on MRI than it actually is.

Radiological Recommendation In TBM:

Surgical planning therefore, involves meticulous preoperative radiological tumour mapping. A high-resolution,non-enhanced bone algorithm temporal bone CT and contrast-enhanced MR imaging are recommended for this purpose.

For early disease confined to the EAC, CT is sufficient. CT can also readily detect erosion of the bony external auditory canal, which is often the first sign of local spread of tumour. Axial and coronal sections are routinely acquired. Sagittal reconstruction may provide additional value for complex tumour infiltration of the temporal bone.

However, CT is inadequate to demonstrate the extent of tumour spread beyond the EAC. Contrast enhanced MR imaging is thus preferred over contrast enhanced CT.

CONT.

Post-contrast T1-weighted sequencing with fat saturation in the axial, coronal and sagittal planes allows the best evaluation of the extent of tumour spread into the surrounding extra-temporal anatomic landscape.

The entire parotid space should be included for evaluation of echelon lymph nodes.

Intracranial extension is much better seen on coronal sections of contrast-enhanced MR images.

The earliest sign seen on MR imaging is mild dural thickening and enhancement along the floor of the middle cranial fossa in the vicinity of the tegmen tympani. Early dural involvement is difficult, if not impossible, to recognize on CT.

CONT.

Although CT demonstrates erosion of the cortical bone of the inner ear very well, spread into the labyrinth is better demonstrated on MR imaging.

Perineural involvement of the seventh and eighth cranial nerves cannot be diagnosed with confidence without contrast-enhanced MR imaging.

Similarly, MR imaging provides further information on the status of the skull base neurovascularstructures when bony erosions are identified on CT.

finally ,The goal of tumor staging is to group together patients with a similar extent of disease prior to treatment. An accurate staging system facilitates the comparison of treatment outcomes for patients with similar disease severity treated by different modalities and institutions. Conclusions can then be made with regard to treatment efficacy and disease prognosis.

Impact of preoperative imaging and staging on surgical decision:ROAD MAP

Conclusion

Cancer of the EAC is a difficult diagnosis in the presence of chronic otitis externa or invasive forms, so late diagnosis with poor outcome is usually the role.

The Pittsburgh classification has been validated and should be used for staging of these tumours. Clinical examination and imaging (CT and MRI) can demonstrate the main prognostic factors: peripheral facial nerve palsy, soft tissue (parotid) involvement, middle ear involvement and lymph node involvement.

Management consists of a combination of radical surgery and radiotherapy and the prognosis is related to local tumor control. This aggressive treatment is almost always responsible for squeal.

Diagnosis and treatment need to be improved in order to improve patient survival associated with fewer squeal. Modern imaging techniques (PET-CTscan) and new radiotherapy techniques (cyberknife, IMRT)must be evaluated.