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Pneumosinus dilatans.


Pneumosinus dilatans refers to an abnormally large aerated sinus; two other characteristic features of this disease are that the bony walls of the sinus are of normal thickness and there is no evidence of erosion. Most cases occur in the frontal sinuses. We describe a new case of pneumosinus dilatans in a 21-year-old woman. She required no treatment.


Benjamins first described pneumosinus dilatans in 1918. (1) Urken et al further attempted to standardize the definition and understanding of this disease process in 1987 through a series of investigations. (2,3)

Along the spectrum of sinus disease, pneumosinus dilatans lies near hypersinus and pneumocele (3):

* Pneumosinus dilatans refers to an abnormally large aerated sinus. Radiographically, the bony walls of the sinus are of normal thickness, and there is no evidence of erosion.

* Hypersinus refers to a large aerated sinus that does not extend past the realm of normal. Hypersinus is generally asymptomatic, and it requires no intervention.

* Pneumocele is an aerated sinus characterized by notable thinning of the sinus wall. It is the thinning, which can affect either focal or generalized areas of the sinus wall, that differentiates pneumocele from pneumosinus dilatans. (3)

In this article, we describe a new case of pneumosinus dilatans.

Case report

During a routine health assessment examination of a 21-year-old female soldier, magnetic resonance imaging (MRI) detected an abnormally large left frontal sinus with a posterior growth in the anterior cranial fossa that impinged upon the frontal lobe of the brain (figure 1, A). Follow-up computed tomography (CT) confirmed the posterior extension of the sinus, and it also detected superior extension and a widening of the ostiomeatal complexes; no bony erosion or thinning was seen (figure 1, B).


The patient denied symptoms consistent with recent sinus disease (i.e., headache, visual defects, and neurologic deficits) and endocrine disease, and she exhibited no cosmetic deformity. She did have a history of systemic lupus erythematosus. Also, she reported that from age 10 to 18 years, she had experienced significant nasal obstruction, rhinorrhea, and allergic symptoms. At some point during that time, she was diagnosed with nasal polyposis, but she had not undergone any surgical treatment. At the age of 18 years, when she was attending boot camp, a gush of clear fluid emanated from her nose. Immediately after that episode, she experienced a resolution of her nasal obstruction.

On physical examination, no polyp or mass was seen in the nasal cavity. Next, the left frontal sinus was brightly illuminated with the flexible nasopharyngoscope at the level of the nasofrontal duct (figure 2). Flexible endoscopy revealed that the ostiomeatal complexes, maxillary sinus ostia, and nasofrontal ducts were widely patent. No lesion, polyp, or mucocele was visible.


The patient was diagnosed with pneumosinus dilatans. She required no treatment.


Pneumosinus dilatans affects all the paranasal sinuses, but it occurs most often in the frontal sinus. In a series of 51 patients with pneumosinus dilatans, Lombardi et al found 39 in the frontal sinus, 5 in the anterior ethmoid sinus, 4 each in the posterior ethmoid and sphenoid sinuses, and 2 in the maxillary sinus (in some cases, more than one sinus was involved). (4) They also reported that the process was most common in men aged 20 to 40 years.

Several basic hypotheses have been proposed to explain the process of hyperpneumatization, but its etiology and pathophysiology remain poorly understood. Among the possible explanations for the dilation are (1) mucocele growth and spontaneous rupture, (2) the presence of a one-way valve, (3) infection with gas-forming microorganisms, (4) hormonal influences and osteoblastic/osteoclastic remodeling, and (5) congenital defects (5):

* Mucocele growth and rupture. Over time, mucocele growth can cause an increase in the size of a sinus cavity. Subsequent rupture and drainage of the mucocele can result in an empty, enlarged sinus. Our patient reported a history of nasal obstruction that was relieved after clear fluid spontaneously rushed from her nose. Her CT showed significant bony remodeling that was consistent with a history of significant nasal polyposis or mucocele. When we correlated this history with the findings on physical examination, pneumosinus dilatans was high on our list of differential diagnoses.

* One-way valve. Ball-valve mechanisms behave in a similar manner. Air pressure is allowed into the sinus, but its release is prevented by the presence of an obstructing polyp, mucosa, or anatomic aberration, leading to a large, aerated sinus.

* Microorganisms. It has long been postulated that infection with gas-forming microorganisms could lead to the development of large aerated sinuses, but there remains a paucity of data in the literature to support this theory? Our patient exhibited no evidence of ongoing sinus infection at the time of presentation.

* Hormonal influences and bone remodeling. Hormonal changes can similarly cause dilation and growth of the frontal sinuses because of promotion of osteoblast and osteoclast activity. Growth factors stimulate new bone formation on the internal surface of the inner table and external surface of the outer table. The character of the frontal sinus bone is important in the development of aeration. Thicker frontal bones, such as those seen in osteopetrosis, tend to form smaller, less aerated sinuses. (6)

* Congenital defects. Congenital diseases that are characterized by a thin frontal bone cortex--such as McCune-Albright syndrome (5) and osteogenesis imperfecta (6)--can lead to dilation of the frontal sinuses. At the same time, there is intensification of the normal resorptive activity along the internal surface of the outer table and external surface of the inner table. (6) This dynamic remodeling enlarges the diploic space. Acromegaly, Lawrence-Seip syndrome, gonadal dysgenesis, Klinefelter syndrome, Turner syndrome, and Prader-Willi syndrome are among those conditions that can contribute. (6)

Most patients with pneumosinus dilatans of the frontal sinus present with frontal bossing; other times it is found incidentally on radiographic imaging. Less common symptoms include sinus pressure (especially with a change in altitude), diplopia, and headache. When the cause is apparent, treatment should be directed toward it. Otherwise, treatment is largely cosmetic to reduce the amount of frontal deformity. (7)


(1.) Benjamins CE. Pneumosinus frontalis dilatans. Acta Otolaryngol (Stockh) 1918;1:412-22.

(2.) Urken ML, Som PM, Lawson W, et al. The abnormally large frontal sinus. I. A practical method for its determination based upon an analysis of 100 normal patients. Laryngoscope 1987;97:602-5.

(3.) Urken ML, Som PM, Lawson W, et al. Abnormally large frontal sinus. II. Nomenclature, pathology, and symptoms. Laryngoscope 1987;97:606-11.

(4.) Lombardi G. Passerini A, Cecchini A. Pneumosinus dilatans. Acta Radiol Diagn (Stockh) 1968;7:535-42.

(5.) Walker JL, Jones NS. Pneumosinus dilatans of the frontal sinuses: Two cases and a discussion of its aetiology. J Laryngol Otol 2002:116:382-5.

(6.) Shapiro R, Schorr S. A consideration of the systemic factors that influence frontal sinus pneumatization. Invest Radiol 1980:15: 191-202.

(7.) Klossek JM, Dufour X, Toffel P, Fontanel JP. Pneumosinus dilatans: A report of three new cases and their surgical management. Ear Nose Throat J 2000;79:48-51.

Thomas P. Nowlin IV, MD; Daniel J. Hall, MD; Eric B. Purdom, DO; Michael R. Holtel, MD

From the Department of Otolaryngology, Tripler Army Medical Center, Honolulu.

Reprint requests: Daniel J. Hall, MD, Department of Otolaryngology, (1) Jarrett White Rd., Tripler Army Medical Center, Honolulu, HI 96859. Phone: (808) 433-1086; fax: (808) 433-9033; e-mail: daniel.

The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.
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Article Details
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Author:Holtel, Michael R.
Publication:Ear, Nose and Throat Journal
Article Type:Clinical report
Date:May 1, 2007
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