Dr. Nielsen provides diagnostic and consultation services in the United States and internationally. He is director of the Electron Microscopy Lab in the Immunopathology Service.



Centers & Specialties

Cancer Center

Clinical Interests
  • Bone and Soft Tissue Pathology
  • Electron Microscopy
  • Head and Neck Pathology
  • Frozen Section Pathology
Medical Education
  • MD, University of Iceland Faculty of Medicine
  • Residency, Massachusetts General Hospital|Residency, University of Iceland Faculty of Medicine
Board Certifications
  • Anatomic Pathology
  • Pathology
Foreign Languages
  • Icelandic
  • Boston: Massachusetts General Hospital
Insurances Accepted
  • Aetna Health Inc.
  • AllWays Health (NHP) - ACD
  • AllWays Health (NHP) - PBO
  • Beech Street
  • Blue Cross Blue Shield - Blue Care 65
  • Blue Cross Blue Shield - Indemnity
  • Blue Cross Blue Shield - Managed Care
  • Blue Cross Blue Shield - Partners Plus
  • BMC HealthNet Mass Health MCO/ACO
  • Cigna (PAL #'s)
  • Commonwealth Care Alliance
  • Fallon Community HealthCare
  • Great-West Healthcare (formally One Health Plan)
  • Harvard Pilgrim Health Plan - ACD
  • Harvard Pilgrim Health Plan - PBO
  • Health Care Value Management (HCVM)
  • Humana/Choice Care PPO
  • Maine Community Health Options (MCHO)
  • MassHealth
  • Medicare
  • Medicare - ACD
  • OSW - Maine
  • OSW - New Hampshire
  • OSW - New York
  • OSW - Rhode Island
  • OSW - Vermont
  • Private Health Care Systems (PHCS)
  • Railroad Medicare
  • Railroad Medicare - ACD
  • Senior Whole Health
  • TriCare
  • Tufts Health Plan
  • Unicare
  • United Healthcare (non-HMO) - ACD
  • United Healthcare (non-HMO) - PBO
  • Well Sense Pediatrics

Note: This provider may accept more insurance plans than shown; please call the practice to find out if your plan is accepted.

Patient Age Group
Provider Gender


Dr. Nielsen has written extensively on neoplastic and non-neoplastic diseases and of bone and soft tissue. He is the co-author of several book chapters, has participated in writing a number of sections over the last few years for the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone, and co-authored Diagnostic Pathology: Bone. Dr. Nielsen is a regular speaker at national and international pathology and orthopedic courses.

Research & Publications

Research Summary

Research interests include pathology and biology of bone and soft tissue tumors and the application of ancillary studies in the diagnosis of bone and soft tissue neoplasms. Dr. Nielsen is especially interested in chordoma research.  For more information about research concepts, co-authors, and to see a timeline, visit Dr. Nielsen's profile at the Harvard Clinical and Translational Science Center.


View my most recent publications at PubMed


Pathology Associates
55 Fruit Street
Boston, MA 02114-2696
Phone: 617-724-1469
Fax: 617-726-9312