Enhanced magnetic resonance imaging and subtraction techniques in postoperative evaluation of craniofacial resection for sinonasal malignancy.

The use of magnetic resonance imaging (MRI) enhanced with gadolinium. and diethylenetriamine pentaacetic acid (DTPA) in the preoperative evaluation of sinonasal malignancy is well established and has an accuracy of over 98%. Since 1979, 208 patients have undergone craniofacial resection at London's Institute of Laryngology & Otology, primarily for sinonasal neoplasia affecting the anterior skull base. Thirty-five "high-risk" patients had MRI at follow-up. The MRI scans were assessed before the patients were examined under anesthesia. MRI was assessed before examination under anesthesia and the results compared with histologic findings demonstrating a reasonable degree of positive correlation but one which is inferior to that found preoperatively (80%). An extension of this technique using the subtraction of T1-weighted MRI with Gd-DTPA highlights areas of increased vascularity, which significantly improves the ability to predict recurrence at the skull base and above the surgical repair in the anterior cranial fossa (94%).

The diagnosis of inflammatory sinonasal disease.

A prospective study was carried out on 25 consecutive patients referred to an outpatient clinic at The Royal National Throat, Nose and Ear Hospital, with a medical letter suggestive of sinusitis, to test the hypothesis that the diagnosis of inflammatory sinus disease could be made simply and accurately by employing systematic nasal endoscopy and a series of plain sinus X-rays. The study compared the diagnostic yields of the history, rigid nasal endoscopy and plain sinus films with computed tomography. All the investigations were performed on the same day. The interobserver variability between consultant ENT surgeon, senior registrar and registrar were compared. With heightened concern over the radiation exposure patients are receiving for medical investigations, the radiation exposure was determined for a selected group of patients. This study demonstrated that in the diagnosis of inflammatory sinonasal disease the clinical assessment correlated with the CT findings in over 90 per cent of cases. This accuracy was dependent on the experience of the clinician in using rigid nasal endoscopy. Interobserver variability ranged from 71 to 90.4 per cent in the correct diagnosis of underlying sinus disease. Close agreement was seen with the interpretation of CT scans. The concordance rate between plain films and CT scans was 87 per cent when reported by a consultant radiologist. This is in close agreement with previously reported studies. The average radiation exposure of coronal CT scanning was 218 times the dose for plain sinus X-rays.

Subtraction gadolinium enhanced magnetic resonance for head and neck imaging.

The subtraction method of Des Plantes has been applied to gadolinium enhanced magnetic resonance imaging (GdMR). Using short acquisition times, T1 weighted spin echo pulse sequences are made immediately before and after the intravenous administration of gadolinium DTPA. To avoid moving the patient from the scanning tunnel the venipuncture is made into the dorsum of the foot. The needle is placed in the vein prior to putting the patient into the scanner and is irrigated with saline while the control series is obtained. 42 patients with naso-sinus or skull base tumours have been successfully investigated by this technique and satisfactory subtraction studies are now obtained on all patients other than the claustrophobic. Subtraction GdMR provides the best demonstration of the effects of gadolinium DTPA on the magnetic resonance signal for both normal and abnormal tissues. The signal recorded on the subtraction image is dependent on tissue blood supply and provides a more accurate record of tumour extent than that shown by unsubtracted GdMR scans.

An intensive field trial to assess hazards to birds and mammals from the use of methiocarb as a bird repellent on ripening cherries.

: A field trial was carried out in Kent, UK, in 1980, to assess the possible hazards to wildlife of methiocarb used as a spray to protect ripening cherries from damage by birds. A broad range of studies was undertaken on a single site subjected to a series of five applications. Ground deposition was measured by analysis of strips of chromatography paper and petri dishes placed between lines of trees. Airborne drift was measured on targets up to 11 m above the ground, and methiocarb residues were measured in samples of cherries. Birds were captured by intensive mist-netting throughout the trial, and breeding success was monitored in nest boxes and natural nest sites. Livetraps were set to catch small mammals in the orchard on five occasions during the trial. Systematic searches for possible casualties were made, resulting in the discovery of 21 birds found dead or incapacitated. Levels of activity of plasma, liver and brain esterases were measured in samples taken from several species, and liver slices from House Sparrows, Starlings and Thrushes were examined histologically for signs of cell damage. Samples of breast muscle tissue from Starlings and House Sparrows were analysed by GLC for residues of methiocarb and its principal breakdown product, methiocarb sulfoxide. Overall, the trial revealed that many birds and mammals were exposed to methiocarb, but its effects were largely transient and sublethal. Even a heavy repeated programme of spray applications did not cause any serious hazard to wildlife populations.

The imaging characteristics of naso-sinus chondrosarcoma.

Eighteen patients with histologically-verified naso-sinus chondrosarcomata are reviewed, emphasizing their CT and MRI appearances. These tumours present with a soft tissue mass expanding and destroying bone and typically (89%) showing areas of nodular or plaque-like calcification on CT. The magnetic resonance characteristics are more specific and when present with the typical CT features are diagnostic of chondrosarcoma. They combine high signal on T2-weighted sequences, with differential enhancement on post-Gadolinium T1-weighted scans. The contrast enhancement is seen at the periphery of the tumour and the central chondromatous core does not enhance. These changes are dependent upon the vascularity of the tissues concerned and have been correlated exactly with the histopathology of the resected tumour specimens.

The demonstration of glomus tumours by subtraction MRI.

Thirteen patients with 14 glomus tumours have been examined by subtraction gadolinium-enhanced magnetic resonance imaging (MRI), with T1-weighted MR sequences before and after intravenous gadolinium-DTPA. To eliminate movement between subtraction pairs, the patient remains in the tunnel of the imager during administration of the contrast medium, and the venepuncture is made into the dorsum of the foot. The effect of the subtraction process is to remove the NMR signal from the final image so that the photographic densities recorded are dependent on the vascularity of the tissue concerned, normal or abnormal. A particular advantage is the removal of fat signal: the low vascularity of adipose tissue ensures that it is recorded as of minimal density. The extent of skull base glomus tumours has been shown optimally by this technique. Subtraction can also help differentiate glomus tympanicum from glomus jugulare lesions, which may be of crucial importance when deciding the surgical approach. In addition to diagnosis, the technique is also important post-operatively, when imaging is needed to show residual or recurrent tumour and to monitor the effects of radiotherapy.

The investigation of acoustic neuroma.

Gadolinium-enhanced magnetic resonance (GdMR) is the long awaited, easy and definitive investigation for imaging or excluding small acoustic neuromas. However, on the grounds of cost alone it is unrealistic to submit every patient with mild unilateral sensorineural deafness to GdMR. A screening regime is described which combines simple but effective imaging studies of the internal auditory meatus with clinical testing of vestibular function and objective audiometry. The 'two out of three positive' approach based on these tests has proved to be a reliable screening regime for selecting patients for GdMR.

Subtraction magnetic resonance for tumours of the skull base and sinuses: a new imaging technique.

A new imaging technique is described, in which photographic subtraction as practised in angiography, is combined with Gadolinium enhanced Magnetic Resonance (GdMR) imaging and applied to the investigation of the paranasal sinuses and skull base. The densities on the subtraction image are dependent upon the blood supply of the tissues examined, thus producing a record of their vascularity: in effect a vasculogram. The method has proved to be technically feasible, and is advantageous in certain situations, particularly those in which the anatomy is complex as in the skull base or where normal structures have been distorted by previous surgery. The technique provides a more accurate record of tumour extent than that shown on unsubtracted GdMR scans.

Radiological study of primary spontaneous CSF rhinorrhoea.

A radiological study of skull base anatomy was performed in patients presenting with primary spontaneous CSF rhinorrhoea. Radiology correctly identified the fistula site in 90 per cent of cases. Contrast CT imaging was found to be the most suitable technique for identifying the presence and site of CSF fistulae. However, pre-contrast bony dehiscences were identified in all patients leaking from the cribriform plate region. More significantly, all of these patients showed deviation of their crista galli, a radiological sign hitherto unreported. These findings support the theory that congenital bony dehiscence is the aetiological basis for this condition. The importance of radiology in the management of this condition is emphasized.

CT of the paranasal sinuses and functional endoscopic surgery: a critical analysis of 100 symptomatic patients.

CT scans of 100 patients from the Rhinology Clinic at the Royal National Throat, Nose and Ear Hospital were reviewed in order to test the precepts forming the basis of functional endoscopic sinus surgery, especially as they relate to the radiological investigation. These were: (a) the site of origin of sinus infection, (b) The relevance of certain anatomical variants in the middle meatus to sinus infection and (c) The use of CT as the radiological method of diagnosis in all cases. Obstruction in the middle meatus and ostiomeatal complex was associated with an increased incidence of opacity in the sinuses but the primary site of disease was not established: the concept that sinus disease takes origin in the middle meatus was not proven. Anatomical variants in the middle meatus were not associated with an increase in sinus opacity and there was no evidence that these anomalies have any effect on sinus disease by causing middle meatal stenosis. The radiological assessment of patients with inflammatory naso-sinus disease should start with plain X-ray. CT is unnecessary as a routine examination. It should be reserved for the pre-operative assessment of patients for endoscopic surgery, its main function being to show important anatomical landmarks.

Polytomographic radiology in the diagnosis and management of maxillary antral disease as determined by antroscopy.

Plain radiology of the maxillary sinus correlates poorly with pathological conditions affecting it as shown by subsequent endoscopic assessment. Tomographic radiology provides a much higher diagnostic yield and in particular is of great value in assessing the 'opaque antrum'. The false positive rate is similar in the two techniques but tomography yielded no false negative diagnoses in this study compared with an incidence of 31% with plain radiology. Sinoscopy remains the definitive method of assessing antral disease but tomographic radiology is a highly accurate screening technique. It provides this accuracy at low cost, low orbital irradiation and more convenience than the newer techniques of CT and MRI scanning which are still not widely available for routine ENT use.

CT of the paranasal sinuses: study of a control series in relation to endoscopic sinus surgery.

A control series of biplane CT scans of the paranasal sinuses, derived from patients examined for orbital tumours, is described. The scans were assessed for the presence of anatomical variants in the middle meatus, said to contribute to meatal stenosis, and for signs of asymptomatic infection revealed by the presence of clouding or mucosal thickening in the sinuses. Of the anatomical variants, only concha bullosa (pneumatisation of the middle turbinate) was associated with a high incidence of infection in the sinuses (85 per cent). Evidence of asymptomatic sinus infection was as high as 39 per cent overall, the highest incidence occurring in the ethmoid cells (28 per cent). Isolated ethmoid clouding on CT was observed in 15 per cent and is likely to be found in as many as one in seven of the adult population in the UK. It is concluded that in the majority of patients clouding confined to a few ethmoid cells shown on CT is without clinical significance. The evidence from the control series did not support the concept that most sinus infection starts in the middle meatus. The presence of a large reservoir of quiescent or chronic sinus infection in the control group suggests that in most instances sinusitis derives from a recrudescence of this pre-existing infection.

Magnetic resonance with gadolinium DTPA for the investigation of temporal bone tumours.

The membranous labyrinth and 7th and 8th cranial nerves are well shown by magnetic resonance scanning but the lack of bone detail makes MRI secondary to CT for the investigation of lesions of the petrous temporal bone. Twenty-two intrinsic temporal bone tumours were examined by magnetic resonance in this study. Seven glomus tumours, one facial neuroma and one carcinoid tumor received intravenous gadolinium DTPA. All showed signal enhancement although the practical value of this enhancement was variable. The ability of MRI to demonstrate the jugular bulb separate from a glomus tumour confined to the middle ear, and signal enhancement of another middle ear tumour after partial removal are described, as well as the tissue characterization for discriminating between cholesteatoma and cholesterol granuloma for mass lesions in the petrous apex.

Magnetic resonance imaging of paranasal sinus tumors for craniofacial resection.

Computerized tomography (CT) has been shown to be 78% accurate with respect to anatomic extent of tumor when correlated with operative findings and histology in patients undergoing craniofacial resection. To determine whether preoperative evaluation could be improved by the combination of CT and magnetic resonance imaging (MRI), 26 patients with tumor of the paranasal sinuses had undergone MRI before surgery in addition to CT. Ten patients also received Gadolinium-DTPA as a contrast-enhancement agent during MRI. The radical approach offered by craniofacial resection allows accurate evaluation of imaging techniques and when these are compared with histologic findings, a 94% correlation is found. The use of Gadolinium further improves the accuracy of tumor delineation to 98%. Despite the intrinsic disadvantage of absent bone detail, MRI demonstrates the extent of tumor better than CT and can distinguish it from inflammed mucosa, retained secretions, and normal mucosa provided the correct sequences are used.

Diagnostic imaging of the nose and paranasal sinuses.

There are four principal modalities now used by the Radiologist to investigate the nose and paranasal sinuses. These are: plain X-ray, conventional tomography, computerised tomography (CT), and magnetic resonance (MR). Plain X-ray is the initial examination, and is used as a screening procedure before employing one of the tomographic techniques. Conventional pluridirectional tomography has now been superseded by CT scanning, which has the advantage of providing both good bone detail and soft tissue imaging. Since the introduction of magnetic resonance (MR), this technique has replaced CT as the optimum method of showing the extent of soft tissue tumour in the sinuses. The introduction of the paramagnetic contrast agent Gadolinium (Gd DTPA) has improved its accuracy. In the anterior fossa discrimination between cerebral oedema and tumour invasion is better shown, and in the sinuses tumour is more easily identified from retained secretion and inflamed mucosa. The best method currently available to show pathology in the nose and sinuses is a combination of GdMR and CT: the former to identify the soft tissues and the latter to show bone changes.

Magnetic resonance imaging of the nose and paranasal sinuses.

Seventy-five patients with a wide range of sinus disease have been investigated by magnetic resonance (MR): these included congenital conditions, allergic and inflammatory sinus disease, fungus infections, and the necrotizing granulomata. In addition, a variety of benign and malignant tumours have been examined, and in the more recent sinus malignancies the paramagnetic contrast agent, Gadolinium (Gd) DTPA (Schering Health Care) has been used. This experience of magnetic resonance scanning has shown that it is superior to computed tomography in demonstrating the extent of malignant disease in the nose and sinuses; most especially when Gd DTPA is used, reaching an accuracy of over 96% by biopsy correlation. An additional advantage of this technique is the wide coverage of the head and neck for the assessment of malignant disease, provided by direct 3 plane imaging and the multislice facility. The main disadvantage of magnetic resonance of the sinuses is the poor demonstration of calcification and bone. For this reason the MR scans may need to be augmented by high resolution CT performed specifically to show bone detail.

Olfactory neuroblastoma: imaging by magnetic resonance, CT and conventional techniques.

Twenty-four patients with the histological diagnosis of olfactory neuroblastoma have been treated at the Royal National Throat, Nose and Ear Hospital since 1975. The tumour showed a bimodal age distribution and 30% of the patients were under 30 years of age. The imaging characteristics on plain film, computed tomography and magnetic resonance combined with intravenous gadolinium DTPA are detailed. None of the changes described is wholly specific. However, a tumour in the ethmoids and upper part of the nasal cavity, which expands into the orbit and erodes the roof of the fronto-ethmoid complex or cribriform plate unilaterally in a young patient, is highly suggestive of olfactory neuroblastoma, particularly if this is combined with the magnetic resonance signal characteristics of a vascular tumour. The typical MR features are those of an intense signal on pre-contrast T2 weighted spin echo sequences and strong enhancement after gadolinium on T1 weighted sequences. A characteristic feature of the response to gadolinium is an enhancement of tumour higher than that of turbinate mucosa on inversion recovery and less than that of mucosa when T1 weighted spin echo sequences are employed. The extent of tumour in the paranasal sinuses and anterior cranial fossa is best demonstrated after magnetic resonance with intravenous gadolinium and this is now regarded as the most accurate method of preoperative assessment of these patients prior to craniofacial surgery.