Departments of ¹Otorhinolaryngology, Head & Neck Surgery and ²Pathology, All India Institute of Medical Sciences, Raipur, Chhattisgarh, India.

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Hydatid cysts, also known as echinococcosis or hydatidosis are swellings caused by infection of parasite Echinococcus granulosus. Hydatid cyst is commonly seen in the Middle East, South America, North Africa and Australia. Hydatid cysts are mainly seen in two organs, the liver (70%) and lungs (25%) [1]. Less common sites affected by the disease include the spleen, kidneys, bile ducts, mesentery, heart, brain and the musculoskeletal system. Diagnosis of hydatid cysts are mainly based on cross-sectional imaging techniques such as ultrasound, computed tomography (CT) scans or magnetic resonance imaging (MRI) [2-4]. The lesion usually appears as a thin-walled mass with inner membranes and a characteristic cystic look.  Aspiration cytology studies of the cyst are also useful in diagnosis but must be done with caution due to the risk of rupture and leakage of the cyst fluid [5,6]. Serological investigations like ELISA, latex agglutination and immune electrophoresis also play a role in diagnosis [7]. Hydatid cysts of the neck are an exceedingly rare presentation  of  the  disease  accounting  for  less  than  1% of  all reported cases. In this paper a  case  with  an  unusual  localization of  primary  hydatid  cyst  in  the  right  posterior  triangle  region  of  the  neck  is  presented  and  discussed  with  the  aim  of  showing  that hydatid cyst though  rare, should  be  kept  in  consideration  by clinicians  while  investigating  a  case  of  neck  swelling.

A 26-year-old female presented  to  the  hospital with  complaints  of swelling  in  the  right  posterior  part  of  her  neck which  first  appeared  8  years  back [Fig.1]. She visited  a  local  hospital where  swelling  was  diagnosed  to  be  a  hydatid cyst.  She was placed  on  a  course  of  albendazole  for  two  years following which the swelling subsided. Patient was   subsequently asymptomatic until  two years back when the swelling reappeared  at  the  same site.  On recurrence the swelling was insidious in onset and painless, initially the size of a pea  but  gradually  progressed  in  size  to approximately  5×5 cm  in size. There  were  no  complaints  of  pain, dysphagia, difficulty  in breathing,  fever,  weight  loss, or exposure  to  Echinococcus  such  as contact  with  cats  or  dogs.  Other possible differential diagnosis included dermoid cyst,  tubercular lymph  node  and  brachial  cyst.  On  examination  she  was  found  to have  a  swelling  in  the  right  posterosuperior  part  of  her  neck  which  was  around  5×4  centimeters (cms)  in  size  and  extending  upwards  to around  1  cm  behind  the  pinna.  On palpation the  swelling  was  soft,  fluctuant  and  mobile.  An  ultrasound  scan  of  the  swelling  was done  which  revealed  a  multicystic  swelling  with  a  strong  possibility of  being  a  hydatid  cyst.  Subsequently  an  FNAC  of  the  swelling  was done  which  reported  the  swelling  as  being  comprised  of  clear watery  fluid  with numerous  polymorphs  and  calcified  scolices  which were  indicative  of  a  long  standing  hydatid  cyst.  CT  imaging  of  the lesion   was  done  which  showed  the  lesion  to  be  a  well  lobulated cystic  lesion  5.8×4.3×5 cms  in  size  located  in  the  posterior triangle  of  neck   beneath  the  splenius  and  within  the  semispinalis muscle  and  filled  with  fluid [Fig.2].  An MRI  scan  was  also  done  as  per advice  from  neurosurgery  to  rule  out  possibility  of  intracranial involvement  and  involvement  of  the  vertebral  column.  MRI report revealed  the  mass  to  be  a  well-defined,  thick  walled,  irregular cystic  lesion  in  the  posterior  spinal  area  on  the  right  side  of  the neck  in  the  intramuscular  plane.

Under albendazole cover patient underwent surgical excision  of mass  under  general anaesthesia.  An  incision  was  placed  in  the  neck,  subplatysmal flap  was  elevated  and  sternocleidomastoid  and  splenius  capitis muscles  were  divided  to  expose  the  swelling. Intraoperatively  the  cyst  was  noted  to be  thick  walled  mimicking  the  appearance  of  a dermoid cyst [Fig.3]. Swelling  was dissected  away  from  the  surrounding  muscles  and  the prevertebral fascia  posteriorly,  all  margins  demarcated  and subsequently  excised in  and  sent  for  histopathological examination (HPE) [Fig.4].  Special   precaution was  taken  during  procedure  to  avoid  spillage  of the  cystic  components. Procedure was uneventful. Post-procedure, patient  was  stable  with  no  nerve  deficits  and  started  on  antibiotics  and  albendazole.  Patient recovered well and operative site healed without any issue.  She  was  discharged  a  week  after surgery  and  reviewed  with  the  HPE  report  of  the  swelling  after  2 weeks  which  confirmed  the  swelling  as  a  hydatid  cyst [Fig.5].  Albendazole cover  was  continued  for  a  further  3  months  post-operatively  with monitoring  of  her  renal  parameters  to  watch out  for  toxicity.  Patient was asymptomatic with no  recurrence  of  the lesion in follow-up  period.

The parasite Echinococcus granulosus has a unique life  cycle  which  alternates  between  herbivores  and carnivores. The  germinative  layer  is responsible  for  producing  the  scolices  that  represent  the  larval stage  of  Echinococcus  infection [8]. Diagnosis  of  hydatid  cysts  are  made  by  a  combination  of  history taking,  clinical  examination,  imaging  studies,  serological investigations  and  aspiration  cytology.  Ismail  Iynen  et  al.  reported  a  similar  case  of  a  hydatid  cyst  in  the supraclavicular  region  with  no  involvement  of  any  other organs [9]. MRI scans show the multiloculated cystic lesion in neck. Fine needle aspiration cytology yields fluid aspirate and smear shows fragment of laminated membrane, which suggests presence of hydatid cyst [10]. MRI scans of neck can also help in better and adequate surgical panning as surgical  excision  remains  the  treatment  of  choice  for  hydatid  cysts of  the  head  and  neck  region  with  the  best  long  term  results. Medical  treatment  is  mostly  used  to  sterilize  the  cyst,  reduce  the risk  of  intraoperative  contamination  and  reduce  the  chance  of recurrence.  Albendazole  is  the  drug  of  choice  in  medical management  of  hydatid  cyst  although  other  imidazole  derivatives like  mebendazole  may  be  used  as  well. Albendazole  is  usually  given  at  a  dose  of  10 mg/kg/day  for 3-6 weeks  before  surgery  to sterilize  the  cyst [11]. During  surgery  special  care  should  be  taken  not to  spill  the hydatid  fluid. To achieve this, precautions are to be taken which  include  packing  the  operative field  with  povidone  iodine  soaked  sponges,  reducing  the  tension within  the  cyst  by  aspirating  some  of  the  hydatid fluid, instilling  scolicidal  agents  like  hypertonic  saline,  5%  silver  nitrate  or  formalin  in  the  operative  field  and  use  of  a  suction  cone.  After the  operation,  the patient  should  continue  albendazole  for  at  least another  6-8 weeks  to  kill  off  any  daughter  cysts  that  might  have survived  the  procedure  and  thereby  prevent  any  chance  of recurrence.

Isolated hydatid cyst is an exceptional and rare clinical presentation of neck masses, it should be considered in the presence of any cystic mass of the neck essentially in endemic regions. Ultrasound and MRI scans facilitate diagnostic and therapeutic procedures in order to achieve complete surgical excision which is main line of management, although prevention remains the essential treatment.

Contributors: RM, AN: manuscript writing, patient management; NMN, JRD: manuscript editing, patient management; GG, AM: critical inputs into the manuscript; NH: cyto- and histo-pathology, along with manuscript revision. JRD will act as a study guarantor. All authors approved the final version of this manuscript and are responsible for all aspects of this study.

Funding: None; Competing interests: None stated.