Amyloidomas are tumors consisting of localized deposits of amyloid, an insoluble, fibrillar proteinaceous material . There has, however been a paucity in descriptions of its imaging findings in head and neck . In our current case where patient has previous history of nasopharygeal carcinoma, a distinguishment between tumour recurrence and benign lesion like amyloidosis could be difficult. In the literature, there have been circumstances where amyloidosis has been misinterpreted radiologically as chondrosarcoma  but no report has mentioned regarding its distinguishing features from a nasopharyngeal carcinoma. In this article we discuss the differences in imaging appearance of amyloidosis and nasopharygeal carcinoma and how imaging can additionally help in locating the defect in the skull base that cause CSF rhinorrhea and pneumocephalus.
This 49 year old gentleman first presented with epistaxis in November 1996 , underwent endoscopic biopsy and was diagnosed with nasopharyngeal carcinoma. Subsequently he underwent radiotherapy a month later. He was asymptomatic until 2002 when he developed symptoms of allergic rhinitis for which he was treated with antihistamines. His symptoms improved and he was placed on a 6 monthly follow up.
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The patient remained well until June 2006 when he developed cacosmia without epistaxis. CT scan and MRI were performed showing a mass arising from sphenoid sinus with lateral extension to involve the cavernous sinus, inferiorly to involve the nasopharynx and posteriorly to involve the clivus. This mass was iso to hypointense in signal characteristics to muscle on T1 weighted images and hypointense on T2-weighted images (Fig 1A). After IV administration of contrast material, mild enhancement could be seen (Fig 1B). Biopsy of the lesion was complicated by CSF leak. Patient then developed fevers with headache and was treated with intravenous antibiotics. He was then referred to our centre for repair of the CSF leak. A repeat CT scan and MRI in our centre confirmed the presence of bony defect in the sphenoid sinus with CSF leak and pneumocephalus (Fig 2 and 3). Since this lesion did not have the typical appearance of nasopharyngeal carcinoma as it has low signal intensity on T2-weighted images with minimal contrast enhancement.,therefore a biopsy was planned at the time of surgical repair of the CSF leak. Intraoperatively the mass was seen in the left side of the sphenoid sinus with slough. Biopsy of the lesion was taken. The site of the CSF leak was noted and was packed with fat graft from the abdomen. Patient was treated with intravenous antibiotics and the CSF leak resolved.
Histology of the biopsy tissue showed few fragments of a predominantly amorphous hyaline material, with infiltrated by small numbers of chronic inflammatory cells (Figure 4A). In some areas, the fragments showed surface epithelial lining, composed of benign ciliated columnar epithelium. Congo-red positivity was demonstrated, with presence of green bifringence on cross polarized microscopy examination (Figure 4B) The histopathology of the biopsy specimen was confirmed as amyloidosis. Patient was discharged on a 6 monthly follow up.
Fig 1A. Coronal T2-weighted MR image through the sphenoid sinus demonstrates a
slightly hypointense lesion (*) involving the sphenoid sinus and extending
into the left cavernous sinus (long arrow). Fig 1B. Contrast-enhanced coronal T1-weighted
images demonstrate minimal enhancement of the lesion (short arrows). Note the normal
cavernous sinus on the right side (long thick arrow)
Fig 2. Contrast-enhanced axial CT brain demonstrate pneumocephalus in the frontal
Region (arrow) and in the lateral ventricle (arrowhead) following biopsy of the mass.
Fig 3. Reconstructed mid-sagittal CT image demonstrating a mass occupying the sphenoid
sinus (*) with destruction of the clivus (short arrow) and bony defects in the skull base (long
Fig 4A. Histology of the biopsy tissue showed a few fragments of predominantly amorphous
hyaline material, which are infiltrated by small numbers of chronic inflammatory cells.
Fig 4B. Congo-red positivity was demonstrated, with presence of green bifringence on cross
polarized microscopy examination.
Amyloidosis is characterized by idiopathic extracellular accumulation of amyloid in tissues. If the deposition is extensive, it may interfere with organ or tissue function and even lead to death. Amyloid is a linear, nonbranching, fibrillar proteinaceous material that is arranged in a highly organized fashion . Amyloidosis is classified into primary amyloidosis, myeloma associated amyloid, localized amyloid, secondary amyloidosis, familial amyloidosis, senile amyloidosis and dialysis associated amyloidosis [5,9]. In a large review, 70% of the cases were primary, 19% were localized, 4% were familial and 3% were secondary . Secondary amyloidosis is associated with chronic inflammatory conditions such as rheumatoid arthritis, Crohn's disease, inflammatory bowel disease and connective tissue disorders.
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In the head and neck region the localized form is the most common type. Amyloidosis of the head and neck is a benign disease with slow progression. It has been reported that the signal characteristics of amyloid on MR images closely resemble those of skeletal muscle, the structure of amyloid being similar in many ways to the highly organized multilayered, myofibrillar ultrastructure of skeletal muscle. This may be an important differentiating point to differentiate amyloidosis from neoplasms . Most neoplasms have a more fluid structure than that of amyloid and skeletal muscle and thus tend to brighten on T2-weighted images. Other reports of amyloidosis, focal or systemic, describe this loss of signal intensity on T2-weighted images . The exact mechanism underlying the signal hypointensity of amyloid on the long-TR images is complex and uncertain. Gean-Marton et al  suggested that the unique structure of amyloid, the _-pleated sheath plays a role in several ways. First, enhanced T2 decay may result from static or slowly fluctuating internal magnetic fields within adjacent amyloid protons held in fixed positions within the folded protein. These magnetic fields generate local field inhomogeneities, causing the protons to precess at slightly different frequencies. The protons therefore lose phase coherence, transverse magnetization, and, consequently, T2 signal intensity. Second, rapid chemical exchange and spin-spin interactions may occur between the amyloid protein and adjacent water molecules. In chemical exchange, an "in-phase" outside water proton is substituted for a "dephased" proton within the amyloid protein. In spin-spin interaction, energy from a surrounding water proton is exchanged with energy from a spin on the amyloid protein. Unlike chemical exchange, no physical exchange of matter occurs in spin-spin interaction. In both cases, the exchange leads to loss of phase. Because dephased protons are not imageable, a loss of signal intensity occurs. Finally, the amyloid microenvironment is composed of a heterogeneous micromagnetic mixture of collagen, calcification, and vessels as well as the amyloid fibrils. The T2 hypointensity may result from differences in diamagnetic susceptibility. Proton diffusion within the voxel across these intrinsic gradients during interecho time causes their phases to spread out, resulting in an irreversible reduction in transverse magnetization.
The low signal intensity of the mass can thus help to differentiate amyloidoma from other tumors, such as nasopharyngeal carcinoma and chondrosarcomas, because the latter characteristically exhibit high signal intensity on T2-weighted images. The enhancement pattern of amyloidosis demonstrate mixed response. Some authors demonstrate no enhancement in the amyloidosis, although peripheral enhancement pattern has also been reported in certain cases. There are few cases that showed enhancement pattern as in our case [2-6]. Hence enhancement pattern is not a clear distinguishing features to differentiate amyloidosis from other neoplasm.
Symptomatic pneumocranium after transsphenoidal pituitary surgery is rare [7,8]. Potential complications include tension pneumocranium, neurologic dysfunction with increased intracranial pressure and meningitis, of which can be fatal. Tension pneumocranium may be manifested clinically by decreased level of consciousness, headache, seizures, decreased visual acuity, visual field defects, or papilledema. Treatments of pneumocranium include observation, prophylactic therapy with systemically administered antibiotics, insertion of intracranial drains, and repair or packing of the floor of the sella as was performed in our current case.
An important clue to the diagnosis of amyloidoma is the low signal intensity on T2-weighted images which distinguishes it from other lesions. This appearance should lead to biopsy to avoid unnecessary chemotherapy or radiotherapy. A conservative approach to this lesion was subsequently adopted for our patient. Long term outcome is generally favorable if this condition.