CASE REPORT Pneurnocephalus complicating frontal sinus osteoma S Simarak MD B Suraprasit MD Abstract ASenatham MD Pneumocephalus is most frequently caused by head trauma, especially to the paranasal sinuses and mastoid areas. Tumours of the skull base, such as osteoma or pituitary tumour, are less common causes. Since osteoma is one of the more common benign tumours of the nose and paranasal area vvitb the frontal sinus being its most frequent location, special attention should be paid to the examination of this area for frontal osteoma in patients presenting \tVith spontaneous pneumocephalus. Introduction Department of Radiology, Chiang Mai Universify, Thai/and Pneumocephalus is defined as an intracranial gas collection in the ex- tradural, subdural, subarachnoid, in- traventricular or intracerebral com- partment. Head injury and cranial 29 SA JOURNAL OF RADIOLOGY. November 1998 -- ~-------------- surgery were found to account for 74.5% of cases, followed by tumours in 12.9%.1 The majority of tumours implicated in pneumocephalus are sinus osteomas. Although an osteoma is considered to be a benign tumour, it can demonstrate a slow growth pat- tern and may result in intracranial complications such as that demon- strated in our patient. Case report A previously healthy 43-year-old man presented with a two-year his- tory of right-sided headache and weakness of his left extremities. He was first admitted in December 1995 with right temporal and occipital headache for two weeks, followed by sudden weakness of the left upper and lower extremities one week later. Cra- nial computed tomography (CT) scan demonstrated a large subdural pneumocephalus in the right superior frontal region. Frontal osteoma was however not recognized at this exami- nation (Figure 1). The patient refused Figure 1: Cranial computed tomography demon strating a large subdural pneumocephalus in the right superior frontal region. topage30 Pneun,ocephalus c.orripf ic.atirrg frontal sinus osteoma frompage29 proper treatment and was discharged with the clinical diagnosis of intra- cranial abscess. The patient still had headache and weakness of left ex- tremities during the interval and was readmitted in December 1997 - but again refused surgery and was dis- charged. Because of aggravation of his symptoms with additional focal sei- zure of his left extremities, he was admitted again in April ] 998. The motor power of his upper and lower extremities gradually decreased until he was unable to walk. Skull radiographs demonstrated a large subdural air collection in the right superior fronto-parietal region (Figure 2). Cranial CT scan during the Figure 2: Skul/ radiographs demonstrating a large subdural air col/ectlon In the right superior fronto-parietal region. Figure 3: Cranial computed tomography at last admission confirms the presence of subdural air at the right superior frontal region, and also reveals a large osteoma occupying most of the frontal sinus with extension to the left. Figure 4: Tumour fragments shown in the cranial cavity, with tracking of air from the frontal sinus to the subdural air col/ection. most recent admission (Figure 3,4) confirmed the presence of subdural air and also demonstrated a large os- teoma of the frontal sinus, with frag- ments of tumour in the cranial cavity and tracking of air from the frontal si- nus to the subdural air collection. He finally had corrective surgery for re- moval of the osteoma and repair of dural defect with uneventful recovery. Discussion Although pneumocephalus is quite common following trauma to the 30 SA JOURNAL OF RADIOLOGY. November 1998 paranasal sinus and mastoid areas,spon- taneous pneumocephalus, on the con- trary, is quite rare. One cause of spon- taneous pneumocephalus is the well- recognized complication of osteoma of the paranasal sinuses which was first reported by Cushing in 1927.2 Osteoma of the paranasal sinuses is a histologically-benign neoplasm. The frontal sinus is the most frequent location, accounting for 75-80% of osteomas in the paranasal sinus re- gion.3,4 The most common symptoms of osteon.a are pain and headache, but many osteomas are asymptomatic and are discovered accidentally on sinus radiographs. Complications of os- teoma are rare, but they may cause ocular or intracranial problems such as proptosis, meningitis, brain abscess, intracranial mucocoeles or intracranial pneumocephalus. In spite of their be- nign nature, osteomas may grow slowly and extension of the lesion posteriorly can breach the dura mater, allowing air to enter the cranium lead- ing to life-threatening complications. Koivunen et al4 studied the growth rate of osteomas of the paranasal si- nuses in 44 patients. They found that the mean growth rate of 23 osteomas that were followed up (including 10 static tumours) was 0.91 mm per year, varying from 0 to 6.00 mm per year (SD 1.41) Of the 13 that were grow- ing,the mean growth rate was 1.61 mm per year. Spencer and Mitchell' con- cluded from a follow-up study of fron- tal sinus osteomas over 17 years that the growth rate varies remarkably. Some were stable, while others may grow as much as 6 mm per year. There are two characteristic his- tologic types of osteomas. The most common type is ivory or compact os- teoma (composed of hard dense bone to page 31 Pneurnocephalus complicating frontal sinus osteoma. frompage30 with minimal fibrous tissue) and the other type is the spongy or fibrous osteoma (contained mature cancel- lous bone), which is less common. The diagnosis of intracranial pneumocephalus and paranasal sinus osteoma can be easily made by radio- graphs as well as by CT scans. On ra- diography, paranasal sinus osteomas appear as round or oval, well circum- scribed, highly radiopaque structures. They rarely attain a sizelargerthan 2 cm. The fibrous osteoma, however, ap- pears less dense on radiographs and thus may be confused with a cyst. CT scans demonstrate a homogenous hyperdense mass arising within a si- nus cavity. Radionuclide scanning with a bone agent usually demon- strates an area of homogenously in- tense uptake. Shibata et alb performed Magnetic Resonance Imaging in five patients with osteomas of the skull and found that all osteomas appeared as low signal intensity on Tl W im- ages.The T2W images correlated well with histological findings: dense os- teomas showed homogenous low-in- tensity, while spongy osteomas had high signal intensity areas and mixed signal intensity corresponding to mixed spongy and dense osteoma. The management of pneumocephalus due to paranasal si- nus osteoma is surgical with removal of the tumour and repair of the dural defect. Opinions vary concerning the optimal management of paranasal si- nus osteomas in the asymptomatic individual. Noyek et al 7 performed radionuclide bone scans in frontal si- nus osteomas and recommended sur- gery for patients with "hot" scans, while conservative and follow-up studies can be undertaken in "cold" lesions. Koivunen" suggested that an osteoma in the paranasal sinus should be removed if it shows any sign of growth, if it fills more than 50% of the volume of the sinus or if it causes any symptoms. Rappaport et al 8 also sug- gested removal of the tumour if it were located close to the nasolacrimal duct. Conclusion Although osteomas of the frontal sinus are benign histologically, they can cause serious intracranial compli- cations. In complicated cases, surgery is indicated, while in asymptomatic lesions factors concerning the proper management have been suggested. Acknowledgements The authors wish to thank Prof Malai Muttarak and Prof Wilfred CG Peh for their advice, encouragement and review of the manuscript. References 1. Markham F. The clinical features of pneurnocephalus based upon a survey of 284 cases with report of 11 additional cases. Acta Neurochir, I 967; 16:1-78. 2. Cu hing H. Experiences with orb ito- ethmoidal osteoma having intracranial complications. Slirg Gynecol Obstet, 1927; 44: 721-742. 3. Montgomery Ww. Osteoma of the frontal sinus. AnYl Oto Rlnno! Laryngol, 1960; 69: 245-255. 4. Koivunen P, Lopponen H, Fors AP, Jokinen K. The growth rat of osteomas of the parariasal sinus s. Clil1 Otolaryngol, 1997; 22: 111-114. 5. Spencer MG, Mitchelli DB. Growth of a frontal sinus osteoma. ] Laryl1gol Otol, 1987; 95: 291-304. 6. Shibata Y, Matsumura A, Yoshii Y, Nose T. Osteoma of th skull: comparison of magnetic resonance imaging and histological findings. Nel/rol Med ChiT (Tokyo), l 995; 35(1) 13-6. 7. Noyek AM, Ch ap n ik JS, Kirsh JC. Radionuclide bone scan in frontal sinus osteoma. Aust NZ] Surg, 1989; 59: 127-132. 8. Rappaport JM, Attia EL. Pneurnoccphalus in frontal sinus osteoma: a case report. ] Cnolaryngo], 1994; 23: 430-436. British Journal of Radiology Web site he British Institute of Radiology have recently announced the establishment of a Web site at http://www.bir.org.uk, allowing access to The British Journal of Radiology articles before they are published. This is primarily intended for subscribers, but one can preview complete sample back issues at http://www.bir.org.uklonline/sample.html. or apply for a free three-month trial subscription. One is able to view complete articles with hyperlinks to figures and references. This site gives an excellent feel of what will be possible in the future, when more journals become available in electronic format on the Internet. http://www.bir.org.uk 31 SA JOURNAL OF RADIOLOGY· November 1998 http://www.bir.org.uk, http://www.bir.org.uklonline/sample.html. http://www.bir.org.uk