Chronic osteomyelitis of the skull base is a commonly reported pathology in existing scientific literature, but chronic  osteomyelitis of the skull vault (COSV) is a rarely documented disease. We report the case of a 38 years old Afghan  male with a presenting complaint of irregular swelling on the skull vault for six months. The patient had a history of  head trauma one year back with a compound depressed fracture which had been surgically managed then. Physical  examination  revealed  a  15  x  15  cm  hard,  immobile  swelling  with  an  old  scar  mark  over  the  scalp.  Neuroimaging  was  consistent  with  diffuse,  bilateral  frontoparietal  swelling  of  bony  origin,  sparing  underlying  brain  parenchyma.  Surgically  excision  of  the  lesion  was  done  through  a  bicoronal  skin  flap  and  cranioplasty  done  at  the  same  time.  Histological findings of the specimen reported chronic osteomyelitis. However, microbiology revealed no growth in  culture. Patient was discharged on the second postoperative day uneventfully. This case turns minds into keeping skull  vault osteomyelitis as differential diagnosis besides other spontaneous bony lesions; e.g. fibrous dysplasia, osteoma  and giant cell tumours.

Cranial     osteomyelitis     is    an     uncommon     life-threatening   condition  which   can   involve  different   parts   of  skull;   mainly   the  base   of   skull  (anterior,   middle and posterior) and rarely cranial vault.1 Cranial osteomyelitis   has  a   predilection   for  male   gender   (79.9%), immunocompromised, overweight  and  old age population. Diabetes mellitus is the most common comorbid  condition.1, The  most  common causes  of  osteomyelitis in  developing  countries are  paranasal  sinusitis, traumatic  head  injury and  scalp  infections, while  in  developed countries  post-surgical  infections remain the main cause.1Staphylococcus  aureus:      It   is  the   most   common  organism  in  post-traumatic  and anterior  skull  base osteomyelitis   (SBO),   while  Pseudomonas   aeruginosais  more frequently  reported  in middle  and  posterior SBO.1, Patients present with various nonspecific clinical conditions,  with  headache being  the  most common  symptom  seen in  73%  of cases.  Other  complications include  sixth  and seventh  cranial  nerve palsy  (78%),  meningitis (63%),  cerebral  venous thrombosis  (44%) and  cerebral infarction  (34%).2  Management includes  prompt   causative  agent   detection,  broad   spectrum   antibiotics for  eight  to twenty  weeks  and aggressive  surgical  debridement. Prognosis  is  better with  early  diagnosis, surgical  excision  and complete  antibiotic  therapy.1,2SBO is the condition that is encountered commonly, especially  in  low-middle-income  countries, but  skull  vault osteomyelitis  is  a rare  condition.  To the  best  of our  elaborate  literature search  using  PubMed and  Google Scholar, this is the first case of post-traumatic chronic osteomyelitis  of  skull vault  (COSV)  with a  benign swelling on presentation

Case Presentation

A 38-year-old  male  Afghan native  was  sent to  our  outpatient clinic  after  complaining of  frontal  irregular swelling  for  six months.  There  were no  further  related complaints.  On  examination, there  was  a bony,  hard,  irregular-shaped  swelling across  bilateral  supraorbital ridges anteriorly, extending to the mid scalp posteriorly, measuring approximately 15 × 15 cm in size and 3 - 4 cm in height (Fig.3A). There were no apparent pulsations or discharging sinuses. Swelling was firm and somewhat tender,  with  a normal  temperature,  non-reducible,  non-compressible, and non-mobile in any direction. The cough impulse was negative. The patient had a history of head trauma  one  year ago,  with  a compound  skull  fracture and  underlying  hematoma, for  which  he underwent  a   craniotomy  and   evacuation   in  his   home   country.  Computed  tomography  (CT) and  Magnetic  resonance imaging  (MRI)  are shown  in  Fig.1 (A&B)  and  2 (A,  B,  C&D). CT  shows  texture changes  and  abnormal growth  of   bilateral  frontoparietal   bones   whereas  MRI   with   contrast  shows   extensive   heterogeneously   enhancing  lesion  over  bilateral frontoparietal  region.  Based on  the  history, physical  examination,  and imaging  findings, post-traumatic  fibrous dysplasia  and  bone tumour were   the   differentials   under  consideration.   Surgery  was   intended   for  cosmetic   and   diagnostic  purposes.   During surgery, a bicoronal skin flap was raised and a bony lesion was excised, followed by cranioplasty using bone  cement  (Fig.4 D&E),  also  known as  polymethyl  methacrylate (PMMA).  A  15 ×  15  cm hard  bone  lesion with several tiny cavities filled with soft greyish jelly-like substance  was discovered  intraoperatively  as shown  in  Fig.3 (B, C, D, E&F) and 4 (A, B&C). It was an incredibly fragile bone with adhesions to the dura in some spots and widespread bleeding from the dura. A complete excision of the bony lesion was performed, as well as cranioplasty for the bony defect, and two subgaleal drains were placed (Fig.4 F). The drains were withdrawn after one day, and the  patient  was discharged  on  the second  postoperative  day in a stable condition. He was prescribed intravenous antibiotics and asked for follow-up with an acquaintance of Neurosurgery in his own country Afghanistan.

Figure1: Computed Tomography (CT) scan of the lesion, A: Bone window axial view with 3D skull reconstructions showing texture changes and abnormal growth of bilateral frontoparietal bones, B: Bone window sagittal and coronal views showing extensive growth of bilateral frontoparietal bones.

Figure 2:   Magnetic   Resonance  Imaging   (MRI)   of  the   lesion,  A: T1WI  &  T1C+ axial  views  showing bilateral  frontoparietal    hypointense    lesion   on    T1WI    and   heterogeneously enhancing lesion on T1C+, B: T1WI & T1C. coronal views showing the same findings, C: T1WI &T1C+ sagittal views showing the similar findings, D: T2WI & FLAIR axial views showing hyperintense lesion on both views.Findings of histological examination:Gross: Specimen  was  preserved in  formalin  in two  containers:   A):  Bone:   The   specimen  consisted   of   multiple bony  pieces  of tissue  measuring  11.5x8.5x1.5 cm in aggregate. B): Soft Tissue: The specimen consisted of  multiple soft  and  bony pieces  of  tissue measuring  5.5x4.5x1.0 cm in aggregate. Microscopy:  A):  Histological examination  of  sections revealed  viable  and necrotic  bony  fragments reveal  marrow  elements. Mild  chronic  inflammation is evident.  (Fig.5A)  No granuloma  or  malignancy was  seen. B): Histological examination of sections revealed fibrocollagenous tissue  and  bony tissue  fragments. Sheets  of macrophages  were  also seen.  Focal  area of  calcification  was noted.  (Fig.5  B) No  granuloma  or malignancy was seen. Diagnosis:   A):  Bone:   Chronic   osteomyelitis   -  No   features  of osteoid  osteoma  or chondrosarcoma  were  seen. B): Soft Tissue: Fibrocollagenous tissue and bony tissue fragments with focal calcification.Findings  of microbiology:  No  growth was  seen  in Findings of  microbiology:  No growth  was  seen in  culture after 48 hours

Figure 3:    A:   Preoperative    view    of   the    head,    B&C:   Intraoperative  views  of the  lesion,  D&E: Multiple  burr  holes  made,   F:   Bone  cutting   with   high-speed  drill   system. Fig.5: Histological examination sections reveal: A) Viable  and  necrotic bony  fragments  with marrow  elements.  Mild chronic  inflammation  is evident,  B) Fibrocollagenous   tissue  and   bony   tissue  fragments.   Sheets  of macrophages  are  also seen.  Focal  area of  calcification is noted. Consent  for  Publication: Consent  was  obtained from  the patient for the publication of this case report and the accompanying images.

The  gross osteonecrosis  of  the skull  bone  along with invasion into the bone marrow cavity and extra-osseous   environment  constitutes   to   form  the   the   picture of  COSV.3Mortazavi  et al.  classify  the causes  of  cranial osteomyelitis  on  the basis  of  its origin  -  sinorhino-otogenic and non-sinorhino-otogenic causes. It  can  affect children  and  adults both,  post-traumatic  cranial osteomyelitis, a non-sinorhino-otogenic causes, is more common among children than adults.1A  recently  reported study  by  Das et  al.  from India  documents  that male  gender  was more  commonly  affected by SBO and the mean age of included patients at  presentation  was 56.9  ±  10.7 years.2This  gender  predilection is  consistent  with the  case  under study.  However, the young age at presentation in our patient is attributed  to  a road  traffic  accident which  could occur irrespective of the age.A case report documented in Italy on COSV in 2019 also  states the  45-year-old  female  had the  complaints

of  headache and  scalp  wound after  a  road traffic accident. However, our patient did not have a history of  a fever,  headache  or scalp  wound  which are  the  usual manifestations  at  presentation.4.5  This implies  that  it is  possible  for chronic  osteomyelitis  to present  without systemic signs of inflammation and as a local pathology.An Indian study by Das et al. both implicate diabetes mellitus  as  the most  common  comorbid condition  in  patients with SBO, that is 46.62% and 90%, respectively in  their  patients.,2 There were no identifiable medical comorbidities  in  our patient,  except  the history  of  surgery itself a year back.CT  scan is  not  diagnostic of  active  osteomyelitis in  post-traumatic  and post-surgical  cases.  The existing  English scientific literature advocates MRI over CT. MRI plays a key role in defining bone and soft tissue changes  of  skull vault.1  COSV  may present  as  diffuse osteolysis   or   diffuse  bone   thickening.6   Similarly,  bone   thickening   with  hypointensity   on   T1WI  and   hyperintensity   on  T2WI   were   notable  features   in   our patient  on  MRI. Hyperintensity  on  T2WI was  suggestive of chronic osteomyelitis in other cases too.4.5Incomplete    penetrance    of   antibiotics    into    the   medullary cavity and wide range of bacterial resistance makes the treatment of chronic osteomyelitis difficult to manage  medicinally.3 Yang  et al.  propose  that the  ideal  antibiotics to  treat  post-traumatic  osteomyelitis must possess the qualities of wide antibacterial target, maximum  safety, least  allergic  properties and  good  water-solubility,  but not  all  qualities are  possessed  by a  single  antibiotic. Gentamicin  and  Vancomycin are  the  most widely  used  ones. We  opted  for wide  surgical  excision for  the  same reasons,  as  well as  to  improve the cosmetic deformity in our young patient. Augmentation  with  PMMA is  being  practiced for  the  last 40 years and so we did cranioplasty using PMMA.3Culture   negative   SBO  was   seen   in  26.64%   and   39% patients  in  the recently  published  studies.2 Case  reports  on COSV  often  have inconclusive  cultures,4.5but cases of Actinomyces and Klebsiella have also been reported.6.

SCOSV  is one  of  the rare  infections  involving the  head  and neck. It can affect patients of all ages. Scalp swellings without  the  typical manifestations  of  headache, fever  and  scalp ulcers  may  also present  as  COSV. Surgical  excision  with concomitant  cranioplasty  in cases  of  gross involvement  of  cranial vault  and  chronicity shall  be  considered. Acknowledgements:  We are  thankful  to Dr.  Sumaira  Kiran, Dr. Shuja Ikram and Dr. Mujahid Hussain for their active participation  in  the surgical  management  of this  case. 

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