Midline swelling is seen in all except:
Midline  swellings  of  the  neck  from  above  downwards  are: Ludwig's angina, enlarged submental  lymph  nodes, sublingual dermoid and lipoma in the submental region; thyroglossal cyst  and  subhyoid  bursitis;  goitre  of  the thyroid isthmus and pyramidal lobe, enlarged lymph nodes and lipoma in the suprasternal space of Burns, retrosternal goitre and thymic swelling. A dermoid cyst may occur anywhere in the midline.
Lateral swellings according to their sites may be divided into the following regions:

SUBMANDIBULAR  TRIANGLE.— Besides  the  lymph  nodes  and  enlarged  submandibular salivary  gland,  there  may  be  deep  or  plunging  ranula  and  extension  of  growth  from  the  jaw.  
In  the  CAROTID  TRIANGLE aneurysm  of  the  carotid  artery,  carotid  body  tumour, branchial  cyst and  branchiogenic  carcinoma  may  be  met  with.  Thyroid  swellings  will  be  deep  to  the sternomastoid,  a  sternomastoid  tumour  may  develop  in  a  new-born  baby,  
In  the  POSTERIOR TRIANGLE  —  besides  enlarged  supraclavicular  lymph  nodes,  there  may  be  cystic  hygroma, pharyngeal  pouch,  subclavian  aneurysm,  aberrant  thyroid,  cervical  rib,  lipoma  (Dercum's  disease) etc.  

Key Concept:
Branchial cyst is lateral swelling of neck present in the carotid triangle.
Reference: A MANUAL ON CLINICAL SURGERY, S. Das 9th ed page no 369
Blind brachial cyst
Thyroglossal cyst
Submental lymphadenopathy
Substernal cyst